Uptime

Measuring Performance

The Need for Metrics Standardization

by Walter Nijsen, CMRP

Understanding how our plants perform and how well we perform in relation to others often reveals opportunities for improvement, at least in principle. The key question first raised is often, “Are we comparing apples with apples?” If not (as in many cases), the whole exercise of comparison, and to some extent, measurement, becomes somewhat (or completely) meaningless.

 

On top of that, a question that really should be answered first is, “WHY should we measure?”, along with, “WHAT should be measured and HOW?”

The measures we believe are truly important are often referred to as Key Performance Indicators (KPI’s), since, apparently, as the wording implies, those contain key information on performance. But does it, and if so, what precisely is it indicating?

When measuring true performance, a number of questions and preliminary steps need to be taken first:

• Which KPI’s are useful at what stage?

• Is this a leading or a lagging indicator?

• What is the correct definition?

• How will we interpret the results?

• How will you benchmark KPI’s?

 

Why Should We Measure?

Joseph Juran famously said, “If you don’t measure it, you can’t manage it.”

Ron Moore said, “Your measurements should expose your weaknesses – those are your improvement opportunities.”

When asking this question to several persons in an organization, you will typically get different answers.

 

An operational leader or business leader could answer: “to measure our profit and losses, or to understand if we are achieving our goals”. A reliability improvement leader could answer: “to identify opportunities for improvement, or to measure the improvement progress”.

 

Both answers are correct and make sense, depending on your role and interests, because you want to measure and trend the results or the improvements at your facility.

 

“To compare and benchmark between industries or within the company” is also an expected answer.

 

On top of this, there is another important, and mostly forgotten, or at least not identified, reason why we should measure: “To share success, which encourages changes and improvements”.

 

To achieve reliability excellence many changes and improvements need to be made. Some are easy, and some are more difficult, but sharing success will help drive forward these changes. Benchmarking at a facility level, company level or industry level is a part of sharing those successes.

What Should We Measure?

If the “Why should we measure question?” is clear and understood, the answer to “What should we measure?” is simple. Let’s focus only on the maintenance and reliability process. At the end of the day, the financial results, product quality and availability will determine your profit and losses and your business growth. So KPI’s such as, OEE, maintenance cost as a percent of replacement asset value, quality index, on time delivery, production cost per unit produced need to be in place.

 

However, these indicators are lagging indicators, or results indicators, which give a snapshot or update for the moment, but will not tell you what the future results will be, nor if these results are sustainable.

Further, many persons or processes can influence these KPI’s. For example, maintenance cost is influenced by many things, e.g., amount of unplanned breakdowns, amount of pro-active work executed, quality of the executed work, efficiency of the executed work, etc. Therefore, it is important to also implement KPI’s, which tell you something about your potential performance in the future, or so-called leading or process indicators. These indicators are typically used to measure the process improvements that bring us to our new goals.

The leading indicators should show us the direction of future results, or in other words, the leading indicators will tell us if the lagging indicators will get better or worse.

There are three sets of measurable components that make up the maintenance and reliability process at Cargill (See Figure 1: Components of the Maintenance and Reliability Process).

• Behaviors and management processes (people skills, mission and vision)

• Operational execution (operations, design and maintenance)

• Manufacturing performance (availability, quality, cost and benefits)

Each component is a process on its own, which can be measured using both leading and lagging indicators. To determine the quality of each process, the results of each process need to be measured using lagging indicators. To assure good results, we must have good leading indicators – if you do the right things, the right things will happen for the business.

The components of the maintenance and reliability process can also be explained as:

approach, deployment and results.

Manufacturing performance is a (end) result of the (correct) deployment of operational execution. Operational execution is, in part, the deployment of maintenance planning and scheduling, defect elimination, predictive and preventive measuring and follow up.

To understand if these manufacturing performances (results) are sustainable, it is important not only to measure the deployment (operational execution) but also the approach (behaviors and management process).

Without having a clearly defined approach, the result can be, and often times is, based on individuals deploying to their best effort, but without any vision and strategy for the future.

In this context, and as a supply chain, the components of the maintenance and reliability process are both leading and lagging indicators depending on where in the process the indicators are being used.

This simplified view of leading and lagging measures betrays the full value the definition can have. There is a cause and effect relationship between leading and lagging; the action being measured will cause a resulting action or effect, which is also being measured.

This means that a given measure could be both a lagging measure for a previous cause in the chain, and a leading measure for a following effect. There are a series of causes and effects in the chain until the final lagging measures are reached.

The Leading and Lagging Indicator Mapping in Figure 2 shows the concept of an indicator being both leading and lagging.

Preventive Maintenance (PM) Compliance is a lagging indicator, or a result of how much PM work is completed when viewed in the context of work execution.

However, when viewed as an indicator of equipment reliability, PM compliance is a leading indicator of the reliability process. The better or higher an organization’s PM compliance, the more likely this will lead to or predict improved equipment reliability. Similarly, improved equipment reliability will lead to reduced Maintenance Costs, which is a lagging indicator of the maintenance process.

 

Before applying and implementing leading and lagging indictors, the maturity of the facility or company needs to be understood.

 

For example, if you are in a transition stage from reactive to pro-active, then KPI’s like training compliance and percent pro-active work completed are more applicable to use than inventory turns increasing, or maintenance rework reducing, which are typically results of a more mature reliability process.

 

To implement which KPI at which particular moment is unique for each business or location.

Some ground rules need to be considered:

- Focus on leading and lagging indicators for each reliability process component, see Figure 1

- Provide clear definitions and examples

- Assess the operational readiness to implement the KPI.

 

How Should We Measure?

 

When implementing key performance indicators and setting goals, it is a natural human behavior to produce the results you are aiming for. This induces a natural bias to get the results you are targeting. For example, at our company we are measuring percent pro-active work completed, and we are aiming to achieve 80% pro-active work.

Clear definitions with examples are set and the unit of measure is hours. When starting the measurement, plants were only asked to report the percent pro-active work done, and within several months, almost all plants were achieving this number, even though we knew it could not be possible considering the maturity stage of some plants. A thorough review showed that not all plants used “work hours complete” as a unit of measure; that is, some used number of work orders complete, some used actual cost, some included contractors, and some not.

 

So, we made a change in the reporting. Instead of asking plants to report the percent pro-active work completed, we asked them to report actual hours spent on pro-active work and the total actual hours worked.

 

This changed the results completely; some plants captured only 60% of the total hours, which were typically the hours spent on proactive work. The hours on reactive work were not included in the total hours show, and thus a much higher percentage of proactive work was reported done than actual.

Plants not capturing hours at all actually failed to report anything.

Lessons learned on how we should measure are:

- Provide clear definitions and examples, in multiple languages if applicable

- Understand the unit of measure and report the raw data, not the end results

- Use uniform reporting systems

Benchmarking and Standardization

Cargill is a leading company in the food industry with over 1500 locations in more than 80 countries. Comparing and benchmarking within the company and with other industries is a challenge.

During the last 10 years, a major change has been made within the company, from a focus on traditional lagging indicators to more leading indicators.

Cargill has learned a great deal in the last 10 years, and many others can learn and benefit from both these lessons learned and from Cargill’s experience. In fact, these lessons learned drive the process of standardization of key performance indicators.

The Society for Maintenance and Reliability Professionals (www.smrp.org) is a group “by practitioners for practitioners”, who in the last year, has developed standardized Maintenance and Reliability Key performance indicators. Each of these indicators have a clear definition, objective, formula, component definition, qualification and sample calculation developed by experts from several industries world wide, validated and evaluated by practitioners, and are ready for use.

A total of 77 key performance indicators are identified and under development, 21 KPI’s are finished and will be published soon by SMRP. Figure 3 provides several examples of the key performances indicators from the body of knowledge (BoK), including the reliability process component upon which they can be used.

 

Worldwide adoption of these metrics will benefit Cargill, but also all other industries. It will also create transparency and unique benchmarking opportunities within the maintenance and reliability industry.

 

 

Walter Nijsen, CMRP, holds the position of Asst M&R Leader for Cargill grain and oilseeds in Europe. Based in the Netherlands, he is responsible for developing and implementing the maintenance and reliability strategy for about 40 locations across West and East Europe

. During the last 5 years Walter has implemented maintenance best practices, and has been instrumental in building the overall reliability culture and vision for Cargill worldwide by actively participating in maintenance steering committees, conferences, facilitating trainings, developing systems and procedures. He holds a degree in Chemical Engineering and joined Cargill in 1995. He is certified in several predictive technologies, is a certified maintenance and reliability professional since 2003. He is an active member of the SMRP Best Practice Committee.

 

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Finding Hidden Machinery Faults With Operating Deflection Shape Analysis

Case of the Whirling Pump
Finding Hidden Machinery Faults With Operating Deflection Shape Analysis
by Daniel T. Ambre

This article is a vibration case study using Operating Deflection Shape (ODS) and Experimental Modal Analysis (EMA) tools and computer animation techniques to solve difficult rotating machinery problems. Mr. Tim Schuyler and Mr. Steve Werness from Xcel Energy Fort St. Vrain Generating Station requested the services of Full Spectrum Diagnostics to perform a vibration investigation on a vertical river water supply pump whose vibration had significantly increased recently for unknown reasons.

The Fort St. Vrain facility is located in Platteville, Colorado, and was both that state’s only nuclear power plant, and the United States only commercial High Temperature Gas Cooled (HTGC) reactor design. The plant was decommissioned in 1989 and converted from a nuclear fueled facility to a natural gas fueled steam generation facility in 1996. The site added heat recovery steam generator (HRSG), and a second gas turbine in 1998. A third combustion turbine with HRSG was added in 2001, providing a current combined rated output of 720 megawatts. Two more combustion turbines are planned to supply up to 300 additional megawatts.

The generating station has a pair of vertical river water pumps used to control the cooling water in the facility. The P4119 and P4119S units are similar in design, both manufactured by Worthington and driven by Westinghouse 200 hp AC electric motors. Overall vibration levels on the P4119 unit were noted to have "jumped" from a stable trend of 0.150 ips to levels approaching 1.0 ips. The dominant frequency was found to be the 1x response at 1180 RPM. A resonance condition was suspected, however, a history of foundation issues suggested a deeper underlying problem or contributing factor.

Cantilever mounted vertical pump designs will typically have natural frequencies near operating speed points. These so-called "reed" modes are a function of the height of the cantilevered structure (above deck), the length of the pump shaft (below deck), the mass of the drive motor, and the "footprint" of the mount interface structures. Each of these parameters effect the mass and/or stiffness of the overall structure, thus the location of the natural frequencies. Also, as a note, symmetric systems (like this unit) will have two fundamental cantilever natural frequencies (N-S and E-W).

These modes are fairly close together, but may appear below operating speed, above operating speed, or even straddle the running speed point. This makes identification of the modes a top priority in establishing a proper structural correction, if required.

In addition to the planned Experimental Modal Analysis used to detect natural frequencies, an Operating Deflection Shape (ODS) analysis was also planned to investigate the operating characteristics. This analysis is helpful in resolving unbalance, looseness, misalignment, and bowed rotor faults. Operating analysis also provided an evaluation of historical repairs to the pump foundation on these units. Xcel Energy provided periods of both operating and non-operating test conditions for the ODS and Modal analyses, respectively.

Machine Design Information

Drive:

Westinghouse AC Induction Motor

200 HP @ 1180 RPM

Rolling Element Bearings:

Driven Machine:

Worthington Single Stage VTP River Pump

1180 RPM

Direct Drive Coupled

3-Piece Shaft Assembly

2 Spider Bearings

6-Blade Impeller

Capacity 6000 GPM, Total Head: 70 ft

Even though the operating vibration problems were found only on the P4119 pump, natural frequency testing was performed on each unit for comparison purposes.

Experimental Modal Analysis

An Experimental Modal Analysis is a diagnostic performed on structures to determine their natural frequencies, damping, and mode shapes. This analysis is performed with the machinery in a non-operating condition, which limits background vibration from other machinery sources. An impulse (usually a hammer blow) is applied to the structure to impart broad-band energy to the system. This energy functions to excite all of the system‘s natural frequencies, similar to the response of a bell or tuning fork to a sharp impact. This hammer has a load cell built into the head that measures the force parted to the structure and allows this signal to be compared to the accelerometer response, via a transfer function, resulting in a measurement of the frequency response of the structure.

Given enough response locations, each system’s natural frequency can be curve fitted and its mode shape animated with specialized modal analysis software. The Mode Shape is an effective visual representation of the deformed structure when amplified by a driving force.

The natural frequency analysis of each unit revealed some curious results. The problematic unit (P4119) appeared to have significant operating margin on its fundamental natural frequency modes. The operating speed was well above each mode. In addition, the secondary unit (P4119S) had no amplified response; however it was operating smoothly at a point between its EW and NS cantilever modes, and with significantly less speed margin?

A summary is presented in Tables 1 and 2. Figures 2 & 3 show the measured natural frequencies in relation to the operating speed (cursor).

Vibration levels in the P4119 River Water Pump were found to be considerably above the vibration alarm levels typically recommended for a pump of this configuration. The historic overall vibration trend obtained from Mr. Schuyler indicated that the levels had recently increased. Operational vibration velocity levels were measured at 1.0 inch per second (ips) on the motor frame, and up to 1.5 ips on the outboard end (bell housing) of the motor. Typical alarm levels for vertical pumps would be set at roughly 0.290-0.340 ips, depending on vertical elevation. The harmonic content (multiples of 1x RPM) were considered low and acceptable.

From experience with vertical pumps of this type, an amplification of a natural frequency is typically the cause of unexplained vibration response(s). The symmetric cantilever design dictates that two natural frequencies should be present (inducing North-South, and East-West motions), i.e., the so-called "reed" modes of the pump. The biggest dilemma in correcting resonance problems is defining the locations (frequencies) of the modes. The two dominant corrective methods used to alter the natural frequency in resonant systems are the addition of a stiffness (bracing) and/or addition of mass to the physical structures. Unless the natural frequencies are first defined, the wrong correction method may be applied resulting in increased vibration levels instead of the desired reduction. With symmetric systems (like this one) the worst case is when the operating speed is between the two modes, which increases the potential of inducing additional problems no matter what corrective method is chosen.

In addition to the Experimental Modal Analysis, this analysis included Operating Deflection Shape (ODS) analysis. This test method is described below.

Operating Deflection Shape Analysis

An Operating Deflection Shape is measured with the machine at its’ normal operating condition. This analysis measures the machines’ response at a specific time or frequency. Both amplitude and phase information are collected at various locations on the structure and, via special software, the vibrating "shape" or response of the machine can be animated.

These animations show the analyst how the machine is moving during normal operation. Note that this is not a resonant response of the machine, but its operational response. The forces within the machine are responsible for the motion, or shape of motion measured with this analysis tool. For example, the unbalance response of any rotating system will produce a response or driving force at 1x RPM. Misalignment and looseness generally produce synchronous multiples of running speed (2x RPM, 3x RPM,etc.).

Examining the operating shapes gives the analyst additional insight into the root cause of many vibration related faults. Combining this analysis with an Experimental Modal Analysis is very effective in ruling-out suspected machinery problems associated with resonance.

Analysis & Conclusions

In this analysis, the P4119 pump indicated some unexpected characteristics. Typical resonance amplification will induce a linear response in the direction of, and similar to the mode shape defined in the EMA. The closer the driving force is to the natural frequency, the more mode shape resemblance in each animation.

This characteristic was not found in the ODS animations. In the P4119 pump operating shapes, a "whirling" or "orbital" ODS animation motion was noted. This visual response,along with the seemingly adequate resonant margin, was another indication that this system was unusual.

The whirling orbital motion in Figures 5 and 6 suggested that the excessive vibratory response was NOT due to resonant amplification.

ODS animations near a resonance will typically correspond to the linear mode shape. The animations suggest that the pump rotor (extended below deck) was driving the response in the motor. A possible reason for this is excessive clearances in the seals and "spider" bearings that support the rotor. Significant leakage from a problematic seal in this pump tends to support the theory that radial clearances are larger than desired.

Additional animations without the motor (Figure 6) more clearly show the whirling motion in the motor standoff support structures. The final animation in Figure 7 shows an isolated view of the support base plate structures. The foundation amplitudes suggest that vibration levels are higher than normal; however, the dense measurement mapping confirms that the plates are moving in unison (in-phase).

Out-of-phase motion between plates (grouted interfaces) or bolted joints would imply looseness response. These animations confirm that the foundation is not the source of the vibration problem. The relatively new bolted joints in the base plate are considered acceptable based on this analysis.

The final analysis performed was an "added mass trial" on P4119. Mass is added to resonant systems to alter the natural frequencies. Adding mass (with sand bags) should both reduce the natural frequency, as well as dampen its response via the shifting sand. Since the natural frequency for this unit was below operating speed, adding mass should increase the operating margin. If a stiffener support were applied instead, the likely result would be an increase in vibration since the operating margin would be reduced.

The Xcel Energy maintenance support acquired several sandbags totaling close to 120 lbs of weight. The unit was started up and the bags were stacked on the motor. No change in vibration levels were noted regardless of the amount of sand applied.

The unit was shutdown for a natural frequency (impact) test. The test indicated that the natural frequency at 1027 CPM was shifted lower by the added 120 lbs of mass to 990 CPM, or approximately 6%. If resonance were the root cause of the elevated vibration levels, a significant drop in the 1x RPM amplitude would have been noted during pump operation. This proved that resonance was not the dominant contributor to the excessive vibration levels.

Based on this analysis and discussions with Xcel Energy management and maintenance personnel, it was recommended that the unit be removed and inspected. It was suspected that some internal unseen fault was responsible for the elevated vibration levels.

Disassembly and inspections of the hardware showed that a locked coupling was likely the root cause of the excessive vibration. Continued operation in this "locked" state resulted in significant wear in the spider bearings, the shaft, and rotor bushings. This extra clearance allowed the rotor to "whirl" as a unit, inducing the orbital motion noted above deck.

The operating animations (ODS analysis)proved to be invaluable in isolating the root cause of the rotor problems.

Dan Ambre, P.E. is a Mechanical Engineer and founder of Full Spectrum Diagnostics, PLLC, a Full Service Predictive Maintenance Consulting company. Dan specializes in Resonance detection, Experimental Modal Analysis, and Operating Deflection Shape machinery diagnostics.

Full Spectrum Diagnostics provides Vibration Analysis level I, II, and III training and certification, as well as training in advanced diagnostic techniques. Dan is a certified software representative for Vibrant Technology, Inc., the creators of ME’scope VES software tools. He also provides ME’scope VES Software Training targeting the In-Plant Vibration Analyst.

Animations referenced in this article are available via email at modalguy@aol.com. Please visit www.fullspec.net

There is also an online Modal discussion at MaintenanceForums.com

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RCM & the Sub-Prime Mortgage Meltdown

Turning A Blind Eye
RCM & the Sub-Prime Mortgage Meltdown

by Neil Bloom

You might be curious and wonder what in the world RCM has to do with the current financial crises, so let’s explore what it is that they have in common. As we will see, RCM has a distinct similarity to the current global sub-prime financial fiasco. Many of you have heard about Reliability Centered Maintenance, or RCM as it is called. But how much do you really know about it?

RCM is a logical way of identifying what equipment in your facility is required to be maintained on a preventive maintenance basis rather than a let-it-fail-then-fix-it basis. Many have heard the phrases "don’t fix it until it breaks" or "don’t break it by trying to fix it." There is a grain of truth to these axioms, but they depict a very shallow approach if you are striving to achieve reliability and safety levels for your facility that are the best they can be.

Many plants have tried the "hit-and-miss" approach, or the old "how-we-used-to-do-it" approach, or the "runon-luck" approach to maintenance. These methods will get you only so far until your luck runs out, and the potential for a disaster looms right around the corner.

In the absence of a structured RCM approach, reliability will rest solely on the basis of seat-of-the-pants experience, with a strategy consisting of a best-guess decision process. That approach falls far short of modern-day expectations.

However, in real life everything is not perfect. For example, there is no universally perfect climate or environment. Likewise there is no universally perfect reliability environment. For example, there are those who are responsible for plant reliability that may still be in a relatively early stage of getting their program going. They are really doing the best they can with the resources they are allocated. In meeting and talking with many of the people in this stage of their reliability program development, I am deeply encouraged by their devotion and passion. They are continually striving to do better. They implement predictive maintenance (PdM) in all the ways they can and use the best judgment available to them.

Then there are those reliability professionals that find themselves in a more experienced and progressive reliability environment. These folks have the benefit of being in a more highly developed situation with a greater flexibility to implement more advanced preventive maintenance methods and tools such as RCM.

Even with those employing a methodology such as RCM, there are those just beginning in their journey, there are those who have been through the challenges of attempting to begin an RCM program and then there are those who have successfully completed the RCM process.

RCM originated in commercial aviation and, unfortunately, since it left that industry, it has become a very difficult and costly process. It was never intended to be that way. In fact, RCM today hardly resembles what it was intended to be by its founders Stanley Nowlan and Howard Heap.

It has been conservatively estimated that less than 10% of all RCM programs attempted will succeed. Looking at it another way, over 90% of all RCM programs attempted are destined for failure! For those of you with first-hand experience, who have attempted to implement an RCM program, you understand why RCM has been so difficult.

Remember, there is a major difference between a program such as RCM, which is designed to truly enhance safety and reliability and its cost avoidance benefits, such as avoiding potential disasters….. and a more generic PdM or betterment program which is strictly an economic exercise implemented solely to reduce known costs. There is nothing wrong with PM betterment efforts or using standardized PM task templates.

However, with almost the same amount of effort, one can successfully achieve a true comprehensive RCM program instead of settling for something with far less value and effectiveness.

RCM and Reality

From many decades of first hand experience with RCM and associated preventive maintenance program initiatives, approximately 80% of those people who are contemplating implementing an RCM process to improve their plant reliability, do not have a grasp of what it really is. The majority of these folks have good intentions, however, what they are settling for is a means to convert time-directed overhauls into condition monitoring PdM tasks. Or they want to use cookie-cutter PM templates, or find better ways to schedule their PM’s, or review the 20% of their known problem components that they believe cause 80% of all of their plant problems. I wholeheartedly endorse all of these measures but let me be very clear; these betterment techniques are not RCM.

It’s The Unexpected

It has been proven over and over and over that the vast majority of major disasters that occur… that were not due to either acts of nature, human error, or sheer negligence…were caused either by equipment failures whose consequence of failure was unexpected and never analyzed, or from components which were incorrectly analyzed to be run to-failure. The disasters caused by these two reasons are "surprises" because they were totally unknown, unexpected, and unanalyzed.

In this light, think about the following statement……."Plant reliability and safety is directly related to the existing vulnerabilities that have NOT yet been identified because the failure consequences surrounding those vulnerabilities have not yet occurred. Shortcuts in the RCM process will most likely result in those plant vulnerabilities remaining unidentified until an unwanted event does occur. Real-world RCM is all about finding those vulnerabilities before they can occur and result in an unwanted consequence of failure."1

RCM And The Sub-Prime Mortgage Fiasco

Now that we have a better understanding of what RCM is and what it is not, what does all of this have to do with the sub-prime mortgage fiasco? Can you see how the above quotation can be directly compared to the vulnerabilities that existed in the sub-prime mortgage market? Can you see how shortcuts in the mortgage application process, such as verifiable income statements and job validation not being required, contributed to the debacle? How about the wishful thinking that, through some uninterrupted string of luck, home prices would continue to escalate indefinitely? Can you see how the absence of ascertaining the real vulnerabilities, such as overstating the inherent value assessment and understating the inherent risk of the mortgages that lenders wrote, resulted in a catastrophic failure of the investment banking industry?

The vulnerabilities that existed on Wall Street, prior to the mortgage meltdown, are eerily, yet specifically similar to the vulnerabilities that existed prior to the countless number of plant catastrophes that have occurred previously, and, in fact, vulnerabilities which currently exist in many plants and facilities today!

What can we in the reliability community learn from the mistakes that were made in the financial community?

It is very easy to fall into the mind-set of cruising right along on a wave of "Reliability Nirvana".

What do I mean by this? What I mean is that the plant or facility is humming along just fine without any significant problems. There have been no calamities recently; there have been no explosions, no fires, no fatalities, and no negative front page headlines or litigation concerns. So how does this Nirvana continue?

It usually continues on a prolonged streak of luck. But, at some point in time that luck will run out.

Quite often, plant managers know that all is not right. However, the inertia of the status quo becomes too great to overcome and they continue to depend on that streak of luck. Unconsciously, they may even turn a blind eye to "reliability reality", thinking that since everything is running well today, everything is just fine with their plant or facility. There may even be a reverse incentive to continue to do nothing, since the option of doing nothing saves money in the short term.

Can you see where this faulty logic is taking us?

A Faulty Logic

That same "cruising right along" logic prevailed at our most prestigious investment banks on Wall Street. Let’s look at the makings of that global financial misfortune in detail. Not unlike the plant management with visions of "Reliability Nirvana", the Investment Bank CEO’s and Managers had that same kind of misappropriated confidence without being realistic about the risks involved. They were in what I call a "Financial Nirvana." Many of those in risk management at the leading Wall Street institutions inadvertently set up "blinders" so they could not really peek at the true risks involved in the undertakings they were dealing with.

How about the profits? They were enormous. Sounds a little like some of those folks in a state of "Reliability Nirvana", making more money by doing nothing and cutting costs capriciously.

Did any of those financial leaders really want to challenge the status quo that was bringing in all the money they could possibly hope for? Could they not see, even for a moment, that they were running on luck? Did it take that much insight to figure out that when they loaned money to people who had very little chance of repaying that debt, they were playing all their cards on the hope that home prices would continue going up by the day. And if that upward trend suddenly stopped, they would pay dearly. Surely it didn’t take a genius to see that their formula for success also put them on the brink of disaster?

Those subprime mortgages were further packaged into Collateralized Debt Obligations (CDO’s), then even further re-packaged by the CDO’s into Structured Investment Vehicles (SIV’s). Each financial instrument in the process brought in more money and more bonuses for the Wall Street crowd. At each step of the way the financial leaders turned a blind eye to risks and to reality.

The Similarities Of A Disaster

In summary let’s look at the similarities of the mortgage disaster and the impending equipment disaster just waiting to happen at a plant or facility.

A FALSE STATE OF "NIRVANA":

In the Financial World: Senior management believed their current sub-prime mortgage process could continue indefinitely and their "house of cards" could not fail.

In the Reliability World: Senior management believes their facilities will continue cruising right along and their facility could not incur a disaster.

TOTALLY OBLIVIOUS TO THE REAL RISKS:

In the Financial World: Senior Investment Banking management, without an in-depth understanding of their mortgage underwriting vulnerabilities, were totally oblivious to the real risks involved.

In the Reliability World: Senior Plant and Facilities management, without an in-depth understanding of their real plant vulnerabilities, are also oblivious to the real risks they are taking.

THE PROFIT MOTIVE TRUMPED EVERYTHING ELSE:

In the Financial World: The investment banks on Wall Street were too busy making money to perform a "self-assessment" of their true vulnerabilities.

In the Reliability World: Plant management is often so focused on reducing costs and saving money that they become unmindful of the true vulnerabilities in their plant.

THE ADDITION OF COMPLEXITY AND CONFUSION CAMOUFLAGED THE RISKS:

In the Financial World: The mortgage documents were so complicated that the people in China, Japan, Europe and even here in the USA had no idea of the "exposure to danger" that they were investing in.

In the Reliability World: The PM program becomes so convoluted that it camouflages the real "exposure to catastrophe" in ones plant.

COVERED THEIR EYES TO REALITY:

In the Financial World: They inadvertently put on a set of blinders to prevent seeing the deficiencies that existed in their mortgage lending program.

In the Reliability World: They may inadvertently put on a set of blinders to prevent seeing the deficiencies existing in their preventive maintenance program.

If your plant management team’s primary goal is to "keep things humming along" and only pay lip-service to preventive maintenance, then disaster is right around the corner. While it may not happen on their watch, especially if they are close to retirement, it could quite possibly happen on your watch.

Was there ever a doubt that a "day of reckoning" was going to happen in the financial world with so many billions of dollars being lent to people, many of which had no job and offered bogus applications to substantiate their income? Was there any doubt that home prices could not continue to skyrocket 15% to 20%, year over year over year?

Likewise, was there ever a doubt that a "day of reckoning" was going to happen and cause the hundreds of plant shutdowns, fires, explosions, and fatalities that have occurred due to equipment problems whereby a less than robust preventive maintenance program was in place? Is there any doubt that unanalyzed or incorrectly analyzed failure modes or hidden failures in standby, backup, and redundant systems are just waiting to wreak havoc on our plants or facilities?

Is there any doubt that this situation exists, and just might happen at your plant or facility?

If so, it doesn’t have to be that way.

Different reliability professionals and different corporate organizations will no doubt be at different levels of understanding and different levels of implementation in their quest for achieving reliability. A large number of you are just beginning to realize and understand that the unknown and unanalyzed consequences of failure pose the most serious threat to the safety and reliability of your plant, and to the well-being of your plant personnel.

There is a new wave that is bringing classical RCM back to its simple original roots like it was always intended to be. Many astute Maintenance and Reliability professionals have already begun to realize the benefits of riding this new wave, and let’s hope that many more will ride the wave to reliability success.

Neil Bloom is the author of "Reliability Centered Maintenance – Implementation Made Simple" published by McGraw-Hill. He is a mechanical engineer with over 35 years of both hands-on and senior level engineering and maintenance management experience in RCM and Preventive Maintenance Programs in the commercial aviation and commercial nuclear power industries. He is an international guest speaker on RCM and an Instructor of RCM in the Continuing Education Division at the University of California-Irvine (UCI). Neil provides 3-day RCM Training Seminars/Workshops and can be reached at neilbloom@RCMAuthor.com or (949) 218-1286. His website is

www.rcmtrainingseminars.com

.

References

1. RCM

–

Implementation Made Simple, Bloom, Neil B., McGraw-Hill Professional, (2006)

Download OctNov_Reliability.pdf

Lessons Learned Implementing an Infrared Program

by Jennifer Daugherty and Roger Miller

Arnold Engineering Development Center (AEDC), at Arnold Air Force Base, Tennessee, has focused efforts toward an improved infrared (IR) program. As equipment ages, the need for improving inspections and making work more effective becomes imperative. Infrared inspection of equipment allows equipment health to be determined and tear-down intervals to be driven more by condition at optimum frequencies. This paper discusses lessons learned while implementing an infrared program and passes those lessons on to others that may find it useful. The goal of the IR program is to increase availability and improve equipment health by detecting impending failures.

Arnold Engineering Development Center is the largest ground flight simulation test complex in the world. AEDC is the world’s premier flight simulation test facility, conducting performance tests in aerodynamics, aeropropulsion, hypersonics, rockets, space systems, and technology. AEDC’s mission is to test and evaluate aircraft, missile, and space systems and components at simulated flight conditions. Twenty-seven of AEDC’s test units have capabilities unmatched elsewhere in the United States; fourteen are unique in the world. Facilities can simulate flight conditions from sea level up to 300 miles and from subsonic velocities to Mach 20. AEDC has motors up to 83,000 horsepower and pumps up to 50,000 gallons per minute and compressors with flow rates in excess of 1,000,000 cubic feet per minute. Protecting the equipment to increase availability is imperative. The Aerospace Testing Alliance (ATA) is the operations, maintenance, information management, and support contractor to the Air Force at AEDC.

AEDC has performed Predictive Maintenance (PdM) and Reliability-Centered Maintenance (RCM) for over 20 years. The IR program had been a fragmented program and had experienced trouble overcoming the scheduling and safety issues involved with high-voltage electrical equipment, but to improve equipment health assessment and reduce the cost to maintain equipment, AEDC continues to improve the infrared program that assesses electrical and mechanical equipment. The purpose of this paper is to share some elements of our IR program that may have been originally neglected but have since been determined to be crucial for continued IR program growth and effectiveness. The specific elements this paper covers are the plan, program quality control, safety, and justification.

IR Implementation Plan

One of the most effective ways to improve an IR program is by developing a good implementation plan with the right elements and actually using it. The plan must be solid enough to be used for the growth of the program, and time should be put into developing the plan because it should ultimately include the scope of your program and the map to get there. Many programs have been successfully started without good plans; however, few programs are sustained and grown to their true potential without a solid detailed plan. Certain elements should be included in the plan to ensure that it will give the direction and foundation needed as the program continues to grow.

Every plan must include the program’s mission, vision, and goals. Ensure the goals are tied to the company’s mission. Each goal should support the company’s goals in some way. This is important in showing management that the IR program is in agreement with the company’s goals. It is also helpful to gain an understanding of what the real goals of the IR program should be. Many times goals may not be what originally seemed to be intuitive. Establishing and directing the program toward these goals are paramount.

Once the goals have been established, metrics must be developed to gauge the performance of the IR program. The metrics chosen should be related to your internal and external goals thereby relating them to your type of business. In some enterprises, ROI may be most critical while availability may be more important for others. That is because equipment availability is directly associated with the test length of an aerospace R&D program. One of our goals is to shorten the time required to test at AEDC thus shortening the R&D phase of critical aircraft development. If ROI is chosen ensure to be consistent with assumptions and lean toward the conservative side to improve program credibility. However, don’t be so conservative that the program is undersold.

Another part of the plan should state how quickly you plan to mature the program, including the funding scenarios expected in the future. This will help provide structure for the program and give the company the necessary time to allocate funding. Documenting the maturation plan will build additional credibility and support. The plan will demonstrate that forethought was used in developing the program and that the goals.

Quality Issues

Another very critical part of a good IR program is to ensure that your program appears professional by addressing any quality issues. One of the most obvious ways to ensure high quality for the program is to become procedural based. Procedures document and provide a roadmap for the way data will be collected and analyzed. They help to ensure that IR data is collected consistently and accurately. Procedures should address any equipment calibration issues as well. Procedures give much more control for managing an IR program.

Another way to help ensure that the data collected is accurate is to develop a good qualification program, which should also be included in the plan. It should include expected certifications, training, critical procedures testing required for the job and at least one field evaluation of the technician collecting data. A qualification test may include questions associated with equipment failure identification, knowledge of the IR equipment being used, IR pattern problems, and IR calibration issues. Qualification time periods should dictate a specific time period and qualification records should be maintained. Any qualification and currency issues should be documented and followed. If a technician is removed from IR duties for a period of time they may need to be re-qualified; this could mean simply taking a test or starting the qualification process over.

Consistent data analysis and reporting is another important consideration. Consistent alarming rules should always be used. When the program is in its infancy, use rules that are available from other sources. When issuing reports refer to these sources and ensure the recommendations are based on those rules. Be consistent when reporting findings. Use the rules to identify when a problem exists. Ultimately however, the IR program’s structure should be based on tools e.g. reliability centered maintenance, root cause analysis, and failure modes and effects analysis. Once problems have been identified document the findings and report them using a consistent reporting method. AEDC uses standard database to both document and report findings in a predetermined reporting format.

Understanding both IR and plant equipment builds credibility and accuracy to the program. Both the technician and the analyst should understand the IR equipment being used. The technician should have a good understanding of the effects of emissivity, reflectivity, FOV, effects of surrounding conditions, etc. Without a good understanding, misleading images could lead to a misdiagnosis of equipment. Not only are good IR images essential but the analyst should also understand the plant equipment that is being surveyed. For example, electricians and electrical engineers usually make good electrical equipment surveyors because they understand how breakers, connections, motors, and transformers work.

Safety

Critical to any PdM program is the safety practices. Safety should be considered in all aspects of the IR program. Minimizing technician exposure to hazardous equipment is not just a responsibility but an obligation for the people who work in your program. Putting a technician in unnecessary risks should not be an acceptable part of your program. At AEDC, NFPA 70E compliance is mandatory. Imaging equipment with a high energy rating could no longer be accomplished until IR windows were installed to allow safe access to technicians. The use of windows and mirrors not only improved technician safety but also improved the consistency of data and productivity by greatly shorting the amount of time the technicians are exposed to a hazardous environment. Understanding the potential hazards of electrical equipment is vitally important. Many times the highest voltage equipment may not be the most dangerous. Experienced personnel should calculate arc flash energy levels to determine where potential hazards may be hiding.

Justification

Justification will always be required for the entire life of an IR program. Always be prepared to provide proof that the IR program is working and that company goals are easier to attain using IR technology. It is better to voluntarily provide periodic proof that your program is working than to wait until asked to do so. In some cases, it could be too late to put together your program’s justification after being asked to do so. Decisions may have already been made that could adversely affect the IR program after it is too late to react. Program justification can also be aided by having one or two very simple demonstrations to demonstrate how IR technology works and help the company achieve its goals. Also periodically take a couple of your successful findings and put them on a slide for your management. These will also be useful for management to show to stakeholders. This will help to make management more supportive of the program and will boost support. This can also prove to be very beneficial in those times that extra funds become available. Remember that you are all on the same team and making your management look good usually translates into further funding and support.

Conclusion

In closing, a good IR program includes not just one element but many: a thorough plan, good metrics, control of the quality of your program, smart thinking, working safely, and continuous program justification and self monitoring. Just as important however, is that ability to work well with technicians and management. Strive to build program credibility, management support, and build on the IR program’s strengths. Through continuous improvement and never being satisfied with where the program is currently, a strong IR program can be very beneficial to a company. Many more elements are required than simply understanding IR technology to sustain and improve the program to the next level.

Note: ATA/Arnold Engineering Development Center (AEDC), at Arnold Air Force Base, Tennessee were awarded Uptime Magazine Best Infrared Program in 2007 and Best Overall Predictive Maintenance Program in 2008 

Motor Maintenance Regimes

  Listen, look, but keep them running

 

Excerpted from 100 Years of Maintenance and Reliability: Practical Lessons from Three Lifetimes at Process Plants by V. Narayan, James W. Wardhaugh & Mahen C. Das (Industrial Press)

 

 

 

 

The chain of habit coils itself around the heart like a serpent, to gnaw and stifle it.  - William Hazlitt, Writer and Critic.

 

Author: Jim Wardhaugh

Location: 2.3.3 Corporate Technical Headquarters

 

39.1 Background

 

I left my Far Eastern idyll for cold dark Europe. Those who move the pawns in the corporate headquarters noticed my success in my assignment in the Far East. So they head-hunted me and I joined this elite group. The job was to help locations that were less well performing to make significant improvements. I met Vee Narayan, who was already in this group; later, Mahen Das also joined us.

As an electrical engineer, I had been extensively involved in previous lives for the implementation of computerized maintenance management systems (CMMS). So I became responsible for electrical maintenance and CMMS implementation.

 

An Electrical Engineers’ Conference gave me the opportunity to prompt the collection of some data. In the Far East, I found that motor repairs were a significant ongoing manpower consumer and, hence, cost. I decided to put some effort into collecting data on this subject so that we could make informed decisions.

39.2 Motor Failure Data

 

A few of our bigger locations and the Institute of Electrical and Electronic Engineers (IEEE) had been collecting data for many years. We captured this data and collated them (see Tables 39.1 and 39.2). We found large differences between our numbers and those from IEEE. We can account for these in part by the difference in the ways of collecting data and in definitions. We believe that IEEE figures give a pessimistic view of overall failure rates that one might expect from a professionally-managed site.

The information shows that motors are generally very reliable. There are few electrical failures and most failures are bearing related. The most significant underlying causes of failure are:

• Defective components

• Poor installation/maintenance

• Poor lubrication

• Water ingress

 

 

 

 

 

39.3 Electrical Failures

 

Scrutiny of the data showed three prime causes of electrical failures:

• Catastrophic failure due to bearing collapse and rotor rubbing on the stator

• Water ingress due to cooler leaks or cleaning with high-pressure water hoses

• Breakage of connections (due often to inadequate bracing)

There did seem to be some deterioration of motors with age. This was most apparent in large motors with a high starting frequency. We found that the larger the machine, the higher it was stressed. Manufacturers had algorithms which could predict the end of useful life with reasonable accuracy. For this they needed service and operational data, such as frequency of starts. This might be worth doing for older machines in critical services.

 

39.4 Bearing Failures

 

Scrutiny of the data showed four main causes of (premature) bearing failure:

• Wrong (or inadequate) bearing installed

• Poor installation practice causing initial damage to the bearing

• Poor lubrication regime

• Poor alignment of driver and driven

 

 

39.5 Performance of Seven Motors at Locations

 

We looked at the motor maintenance activities in seven of our companies in six different countries. Each was a company plant built to corporate standards, with most rotating equipment having an installed spare. However, there were a variety of maintenance strategies in place.

 

Figure 39.1 summarizes our findings. It gives the percentage of each site’s inventory of motors removed to the workshop for significant repair each year. These percentages have been broken down by reason for removal:

• Breakdown (i.e., the motor had been run to failure)

• Condition monitoring had indicated imminent failure

• Time-based overhaul regime in place for some or all of the motors

 

Considering this, we found that:

• The large proportion of time-based overhaul activities of Location 7 did not seem to reduce breakdowns significantly.
• Location 6 did seem to be somewhat more effective, but arguably was still not cost effective.

• Location 5 had many breakdowns, even though a significant percentage of motors were repaired because condition monitoring was predicting imminent failure.

• Their condition monitoring did not seem very effective in predicting and/or pre-empting failures.

• The site had an extreme blame culture.

• Location 1 had minimized repair efforts by using run-to-failure as a default strategy.

• The small amount of time-based maintenance was for a very few un-spared furnace fans which were overhauled when the plants were shut down every four or five years.

• This location had a fairly skeptical view of the merits of condition monitoring. They would keep motors running until imminent failure was very apparent.

• What they also had found was that running motors less than 30 hp to failure did not result in significant additional consequential damage and cost compared to pre-emptive action.

• The proportion of breakdowns is fairly constant whether you do condition monitoring and/or overhauls or just let things run to failure.

 

39.6 Summarized Findings

 

From our review, we learned that electrical motors are very reliable. In more detail, we found that:

• Windings do not exhibit significant wear-out unless they are:

• Too frequently started or

• Large and highly stressed

• Winding connections are prone to breaking if not well braced against movement.

• Bearings do wear out, but long life is a function of a few simple things:

• Correct bearing selection (not necessarily the same as found in the machine)

• Correct installation, using bearing heaters etc. to minimize damage

• A good lubrication regime (correct type and quantity of lubricant)

• Correct alignment

• Smaller machines (less than 30 hp) make up the bulk of the population and can be run to catastrophic failure without significantly increasing consequential damage to shaft or windings.

• In many locations, there is a high level of installed sparing so the consequences of failure are low.

• Motor condition monitoring has to be quite cheap; else it is not an economical strategy. We concluded that:

• Vibration monitoring could not be justified for most motors; it became viable (just) if you were already going to check the driven equipment.

• Ultrasound was potentially useful if you had many close packed fractional horsepower motors.

• Winding monitoring could not be justified for most motors; a special justification was needed for critical applications.

• Winding monitoring is improving, so this would be kept under review.

 

39.7 A Maintenance Strategy for Refinery Motors

 

We carried out an evaluation of possible strategies and monitoring techniques. There were many magic bullets being advocated by credible universities, consultants, and large companies.

 

We concluded that for very large critical machines:

• A proprietary monitoring installation that continually monitors vibration, axial displacement, etc., should be the norm.

• Information should be centrally monitored.

• Alarm and trip parameters should be set after agreement with the manufacturers.

• We should do regular (annual) internal inspections, using a boroscope.

 

For the bulk of industrial motors, we concluded that regimes described briefly in Tables 39.3 and 39.4 were justifiable and should be the norm in most environments. Obviously in environments which are extremely arduous, additional steps may be needed.

 

 

 

 

If ultrasound and thermographic tools are available, a minimum effort periodic inspection could be beneficial. They are particularly useful if you have a large number of motors very small, and closely packed.

 

39.8 Lessons

 

• Buy reasonable quality motors which are inherently reliable enough for your application.

• Ensure good lubrication.

• Select correct bearings and install correctly.

• Run small spared motors to failure. Run to failure or at least imminent failure is a very respectable strategy for equipment where the consequential loss is low.

• Predicting and pre-empting failure, however cheap, is only cost effective if you can pre-empt catastrophic failure or major production loss. In general, pre-emptive actions must cost less (and probably significantly less) than the consequential loss due to failure.

• Condition monitoring can be costly and ineffective so you need to audit the effectiveness and cost effectiveness of the system.

• When motors fail, investigate to find root cause and try to eradicate repeat failure causes. (Think correct lubricant, correct lubrication regime, correct bearing, starting frequency.)

 

39.9 Principles

 

Preventive and predictive maintenance are generally sound strategies, but not universally applicable. Run-to-failure strategies are perfectly acceptable in many common situations. Maintenance strategies must be based on a rigorous understanding of the risks of failures, not on current fashions.

How to create a maintenance scrapbook

By Joel Levitt, Author of Lean Maintenance 

The advent and acceptance of digital photography has significantly improved the ability to take historical photos and manage those photos after they are taken. The questions I would like to address are what photos should be taken, how to take them and why.

For most maintenance departments (who don’t have one), a digital camera is high on the priority list. Like computers, the quality has improved and the cost has gone down substantially.

There are several major categories of reasons for keeping an historical record with photographs

General condition: To see if the asset has deteriorated or in any other way changed over time (such as moved, sunk, twisted, etc.).

The second issue in construction is to determine accurately where things are located (such as where the sewer line was actually run), or to document the particulars of construction (was there rebar in place when they poured the footer). There will be a large number of shots, and all have to be described (who, what, when, where, etc.) for the scrapbook to have maximum value. The toughest issue with construction documentation is that the work has to be retrievable five, 10 or 20 years after construction. No one may still be around to tell the current people that this documentation project is available.

After a specific damage, accident, claim or potential claim. Photographs for this category will become evidence for a claim or to defend a claim. A higher level of care is necessary, including:

• Documentation of time and date of shots

• Location from which shots are taken

• Name, affiliations and contact information of photographer

To document large repairs, the photograph(s) should tell the whole story of the repair. Shots taken every hour, shift or day need to be accompanied by a narrative. It is important that the book made up for the repair is stored so that it can be found in a year or two (even five), when the repair is to be done again.

Guidelines for taking these photographs

Before you shoot, think "what would I like to know five years from now about how the asset looks today." If you don’t know some likely answers to this question, find someone who does.

For the first of a series, stand back to show the asset in its correct place. Document who is shooting, when the shot is taken and where you are standing. Write down any other useful information such as weather (if that is relevant).

Use good photographic skills to center the asset and move close in (by zoom or by walking) so that the important parts of the asset fill the frame. The biggest complaint is that the meat of the picture is too small to see anything useful.

Be sure the lighting is adequate to show the level of detail necessary for the asset. Add flash or artificial lights as needed.

If there is a front and back, top and bottom, shoot from a variety of angles.

Always complete the job by building a document and catalog, printing a scrapbook and publicizing its existence. Large organizations are starting to have thousands of photographs that are uncataloged, undocumented and impossible to find and use.

Note to readers: Please join Joel Levitt for a one day Lean Maintenance workshop at IMC-2008 23rd International Maintenance Conference, December 8-11, 2008 at the Hyatt Coconut Point in Bonita Springs Florida

MRO Definitions and Transactions

Excerpted from MRO Inventory and Purchasing
by Terry Wireman, CPMM
Courtesy of Industrial Press, Inc.

Finding Balances in MRO Management

MRO materials management is a decision-making process. It requires balancing financial differences between competing interests.

1. Service Level vs. Stock Out

At a 90% service level, there is a 10% chance that a part will not be available when required. The costs associated with a stock out include lost production (downtime cost), materials expediting cost, reduced maintenance labor productivity, etc.

If the service level is increased to 95%, then there is only a 5% chance that a part is not available. Although this change reduces the probability of incurring a stock-out cost, the additional inventory stocking level increases the capital investment costs, the holding cost, the size (and cost) of the storeroom, etc.

2. Cost of Safety Stock vs. Service Level

The more inventory that a company holds, the higher that its investment cost will be. If a company sets the safety stock at a high level (reorder point = minimum on hand quantity + safety stock), it will incur higher costs. Conversely, a higher investment cost generally corresponds to a higher MRO stores service level.

The question facing a company is “What service level can you afford?”

100% Capital investment too expensive for almost any plant

95% A good target for most companies

90% Downtime cost will be too high for almost any plant

3. Holding Cost vs. Ordering Cost

When larger quantities are ordered, they increase the holding cost, which is based on the total investment in the spare parts. However, ordering costs are lowered, such as paper work, purchasing time, expediting time, transportation, etc. The issue here is to balance the ordering costs with the holding costs.

Issues that Influence the Balance

What are some of the issues that influence the balance between ordering costs and holding costs? The following is a list of the factors.

1. Vendor or manufacturer order fulfillment lead-time

• How much time from order to delivery?

2. Variability of delivery lead-time

• Some times a day, some times a week

• Weather or seasonal-related impacts

3. Service level and safety stock

• Risk of using up all the stock before the order arrives

4. Variability of usage

• The plant used 1 in January, 13 in February, 8 in March

5. Other Issues influencing stocking decisions

• Vendor or manufacturer is prone to labor or strike problems

• Equipment that the spare parts are used on is no longer manufactured

• Geographical location of vendor or manufacturer

There are two general rules that balance MRO inventories. They are:

1. The larger the safety stock, the lower the risk of stock out and the higher the cost of holding inventory

2. The smaller the safety stock, the higher the risk of stock out and the higher the cost of purchasing

Determining Proper Stocking Policies

Based on the type of items that are carried in an MRO storeroom, it can be seen that one policy will not work for all inventory items. Some very expensive items are slow-moving, whereas other very inexpensive items move very quickly.

What are some of the factors that help determine the proper stocking policy for each item? Some of the factors include:

• What is the part?

• How critical is it to plant operation?

• What is its usage pattern?

• Is the part high usage? Low usage? Seasonal usage?

• What does the part cost? Is the part high cost? Low cost?

• Is there a discount for volume order?

• What is the part’s stock out impact?

• How expensive is the downtime?

• How long will the downtime last?

• What is the part’s lead time?

• How long does delivery take after the part is ordered?

Types of Spare Parts

Another way of looking at spare parts is by their part type. In any MRO storeroom, spare parts can be categorized by at least eight different types. These are:

• Bin stock—free issue

• Bin stock—controlled issue

• Critical or insurance spares

• Re-buildable spares

• Consumables

• Tools and equipment

• Surplus parts

• Scrap or useless parts

Bin Stock—Free Issue

Bin stock, free-issue items are typically parts like fasteners, including bolts, nuts, and washers. Pipe fittings may also fall into this category.

These items are usually stored in bins located directly outside the storeroom, where employees can take what they need to perform their jobs without requisitions.

Bin Stock—Controlled Issue

Bin stock, controlled-issue items are items with a little more shelf value than free-issue items. These are items that generally need some control.

They are usually behind the storeroom counter and issued to a requisition.

Critical or Insurance Spares

Critical or insurance spares are parts such as motors, pumps, gear cases, and other large spares. These are usually stored in locations where they can be carefully tracked and cared for so they are not damaged in storage.

Consumables

Consumables are maintenance-related items that are typically used in the performance of maintenance work. Items used during the performance of repair activities may include rags, tape, and speedy dry, etc.

Tools and Equipment

Tools and equipment are typically larger repair tools that are not assigned to a specific individual. These are issued to an employee or work order, then returned when the job is finished.

Surplus Parts

Surplus parts are found in the storeroom and are typically left over from projects or larger maintenance tasks. These surplus items should always be entered into the inventory tracking system before they are stored in the storeroom.

Scrap or Useless Parts

In most MRO storerooms, there are some scrap or useless parts.

These items should be targeted for removal from the inventory system.

ABC Analysis

With this many types of items in the storeroom, how can the proper stocking rules be applied to each item? One tool that is useful in any MRO storeroom is ABC Analysis. This tool focuses on a significant few rather than the overwhelming many.

“A” Items

“A” items are typically of high dollar value, but low usage. These items may make up 80% of the total inventory costs. However, these items will also make up less than 20% of all the spare parts carried. “A” items should have regular reviews of reorder points and reorder quantities, as well as usage trends. All details concerning these items should receive close follow-up. It is important for them to have complete and accurate MRO inventory and purchasing records.

“B” Items

“B” items are of moderate dollar value and have moderate usage.

These items may make up a total of 15% of the total inventory costs.

However, they will typically only be 30% of the total inventory items. “B” items should receive regular cycle counts and tracking; attention should be paid to keeping good transaction records.

“C” Items

“C” items have a low dollar value. These items will make up about 5% of the total inventory value. However, they will make up approximately 50% of the total number of inventory items. “C” items will be the larger part of the inventory. Because they have less value, they will require minimal recordkeeping.

Being able to classify the spare parts in the storeroom into one of the ABC classifications allows the storeroom resources to focus on controlling and managing the most important items.

Order Quantity Rules

When considering the order quantity rules for any of the ABC items, there are at least three sets of rules that can be used. “A” items will typically be controlled by maximum and minimum quantity specifications. “B” items will typically use some type of fixed re-order interval system. They may be reordered weekly, monthly, or quarterly. “C” items typically use a two-bin system. Items are issued out of one bin until it is empty. Then they began issuing from the second bin; meanwhile the first bin is restocked. Utilizing these simple controls reduces the workload in any MRO storeroom.

Lubrication Surveys: Increasing Machine Reliability

By Kristopher Sonne – Trico Corp.

Auditing your facility’s lubrication program is a time consuming, tedious job but in the long run it will increase your machine reliability, save time and save money.  Many companies rely on their lubricant supplier to compile a list of equipment with lubricant and replenishment frequency.  Although lubricant manufacturers and suppliers are a great resource for lubricant information the result of the lubrication survey is generally no more than a cross-over chart from what you were using before.  The outcome from a lubrication survey should be a clear concise list that includes: machine IDs, manufacturers, models, OEM recommended lubricants and frequencies, chosen lubricant, replenishment frequency, and the technical reasons for using the chosen lubricant.

The first step in the process is information gathering and field verification.  The basic equipment list with equipment name, number, manufacturer and model can be easily attained from the facility’s CMMS system.  This information is a good start, but many things can change since the information was entered.  This list is to be taken out in the plant and verified that the information is indeed correct.  While walking down the list the ambient temperature, component temperature are to be taken, as well as, the environment conditions the machine is subjected to (such as outside environment, humid/moist, frequent wash-downs, etc.) and speed.

Once all the equipment information has been gathered and conditions recorded, the next step is more information gathering.  It is now time to hit the facility’s engineering and maintenance office to gather the OEM recommendations from the manufacturer’s operation, installation and maintenance manuals.  Generally the manuals will contain generic or specific lubricants to use and the oil change or re-greasing frequency based on different run times or operating temperatures.  If this information cannot be found, knowing the manufacturer and model number will allow you to download the manual from the manufacturer’s website.  If all else fails, speaking to the manufacturers’ Application Engineer can get you the information you require.  If the lubricant brand and type is what you receive (such as Brand X 100 EP Gear Oil) the product data sheet should be obtained to find out exactly what the lubricant is.  Recording the base oil, type and viscosity (example: ISO 100 EP Mineral Gear Oil) will simplify the process of choosing the lubricant to be used and if any consolidation can be performed.  Other important information to note is the viscosity at 40°C, viscosity at 100°C or the viscosity index (VI).  Understanding how the OEM specified lubricant’s viscosity changes due to temperature is important because with this information the viscosity the machine requires at various operating temperatures can be calculated. 

Most facilities have a favored lubricant supplier, having a secondary supplier is suggested.  Today’s lubricant manufacturers all have good products if applied correctly, but it is rare that one manufacturer will have all the appropriate lubricants for all of your applications.  There may even be specialized lubricants that will require having a tertiary supplier as well.  With the use of viscosity-temperature charts the OEM specified lubricant and the proposed lubricant can be plotted against each other to determine how well they compare.  At this time the information previously collected such as the environmental conditions and even how accessible the equipment is will help in determining if there would be an advantage of using a synthetic over a mineral based lubricant.

In an ideal world the lubricant being used on a machine would be exactly what lubricant the OEM recommends down to the brand.  Lubrication type and frequency is designed in to the equipment.  Equipment designers select the lubricants factoring in speeds and loads.  Straying too far away from their selection, will impact the reliability of the machine by either creating an inadequate lubrication condition thereby increasing the likelihood of metal-to-metal contact between frictional surfaces or by generating excessive heat (and the consequences that excessive heat entail).  If consolidation of stored lubricant products is to be performed at this time, there are many considerations to take in to account.  Criticality of the machinery and its affect on the process is the largest consideration; the more critical the component the less likely you should be to stray away from the OEM specified lubricant type.  If there is any type of drastic change in the lubrication regime of any important piece of equipment extra research and periodic testing of the lubricant while in use is highly recommended.  Even if the base fluids are compatible, there could be compatibility issues between the additives and thickeners (in grease).  Besides compatibility issues between the previous used and new lubricant, compatibility between the new lubricant and the seals should be determined.  Another issue may be the proposed lubricant’s affects on ‘yellow metals’ such as brass gears and bushings.

When it comes to the ‘life blood’ of machines great care has to be taken in all steps of the process.  Basing decisions without the knowledge necessary is a dangerous affair and can lead to severe consequences.  Your equipment OEMs and lubricant manufacturers each know their own products better than anyone else but they don’t know or understand each other’s.  As maintenance professionals these are our machines and it is up to us to insure all the homework has been taken care of.

Why Preventive Maintenance is Important?

Why Preventive Maintenance is Important
Excerpted from Preventive Maintenance (Maintenance Strategy Series) by Terry Wireman CPMM
Courtesy of Industrial Press

If you ask twenty different people to write their definition of preventive maintenance, you will get twenty different answers. The term has varied definitions. For the purpose of this text, preventive maintenance is defined as a fundamental, planned maintenance activity designed to improve equipment life and avoid any unplanned maintenance activity. In its simplest form, preventive maintenance can be compared to the service schedule for an automobile. Certain tasks must be scheduled at varying frequencies, all designed to keep the automobile from experiencing any unexpected breakdowns. Preventive maintenance for industrial equipment is no different.

The Importance of Preventive Maintenance

Preventive maintenance is the foundation of the entire maintenance strategy. Unless the PM program is effective, all subsequent maintenance strategies will take longer to implement, incur higher costs to implement, and have a higher probability of failure. This may seem to be an overstatement, but publications from authors around the world echo the same thought. Because the preventive maintenance program receives this type of solid endorsement from successful companies, it appears that companies would focus on their preventive maintenance programs, attempting to insure their success. However, this is not the case. Figure 1-1 shows the result of a survey that involved 5000  companies. As the figure highlights, the majority were not satisfied with the effectiveness of their preventive maintenance program. How is the effectiveness measured? Effectiveness occurs when 80% or more of the maintenance activities can be planned and scheduled at least one week in advance. This level is an indicator that the organization is moving from a reactive culture to a more proactive culture.

The results of another survey are highlighted in Figure 1-2. This figure shows that the percentage of respondents who believe their preventive maintenance program is ineffective is almost the same as reflected in the survey in Figure 1-1. The issue is that the two surveys were taken almost 40 years apart. Figure 1-1 was taken in 1965 and Figure 1-2 was taken in 2004. Why is there a lack of progress improving the number of companies with effective preventive maintenance programs? It is due to three major reasons.

The first is that companies do not focus on preventive maintenance activities because these activities are not "high profile" or "high visibility" activities. This obstacle is one of the first that companies need to overcome when moving from a reactive to a proactive culture. In a reactive culture, the "hero" technician (the individual who can fix problems quickly) is typically highly valued. The technicians then feel that the preventive maintenance activities are not valued; they will opt to focus instead on their "reactive" skills. This problem is not overcome until upper and mid level managers show they value the preventive maintenance activities more than the "fix it fast" activities. Without this management support, the technicians will always perform the activities that are perceived as the highest value.

The second issue is the pandemic originating from the lack of basic maintenance skills. In the majority of companies today, the maintenance technicians lack the skills to identify developing problems with equipment components. They are unable to perform basic lubrication tasks or even to make proper adjustments to their assigned equipment. This means that even when the organizational culture is conducive to change, the basic skills may still prevent the preventive maintenance program from being successful.

The third reason, the lack of a disciplined development process for preventive maintenance, will be discussed in Chapter 2.

Companies still try to excuse their lack of good preventive maintenance by making statements such as "Preventive Maintenance doesn’t work in our industry" or "Our customers don’t care about our maintenance practices." However, in every industry, there are excellent examples of companies with effective preventive maintenance programs. This calls to mind a quote from a classic textbook "Reengineering the Corporation" by Hammer and Champy. They wrote:

In almost every industry, under the same rules and with the same players, the successes of a few companies rebut the excuses of the many.

This quote is true of the maintenance/reliability business, but is especially reflective of preventive maintenance strategies. There are countless testimonials from companies that highlight the benefits of a good preventive maintenance program. The following material shows some examples from many different industries.

Concerning their equipment uptime, one discrete manufacturing company said: "We improved out equipment uptime from the 50%– 60% range to the 95% + range by instituting a preventive maintenance program." –85% uptime acceptable for the plant’s equipment. The Vice President changed the technician’s thinking by asking "What uptime do you expect from your Chevy Blazer?" Uptime at this manufacturing company now averages 94–97%.–$18 per installed horsepower per year–$13 per installed horsepower per year–$9 per installed horsepower per year—for example, the oil is never changed—it will have a shorter useful life. Because industrial equipment is often even more complex than the newer computerized automobiles, service requirements may be extensive and critical. Preventive maintenance programs allow these requirements to be met, reducing the amount of emergency or breakdown work the maintenance organization is required to perform.

This same company continued on about the benefits by saying "Before the routine shutdowns for preventive maintenance, we were always behind in the production schedule. After we started regular preventive maintenance shutdowns, we began to increase our production efficiencies. As a result, all operations are now shut down one shift per week for preventive maintenance or to do something to improve the process."

The magazine Engineered Systems presented a feature article on maintaining properly levels of humidity in a facility (a typical preventive maintenance function). The article noted, "Both people and equipment can cost companies thousands, if not millions, of dollars if the relative humidity is not maintained within the recommended guidelines." This article provides good insight into the ancillary financial contributions that an effective preventive maintenance program can have on a company’s bottom line.

The magazine Business Week featured an article on an electronic manufacturer, where it was observed "By developing a fixed pattern for preventive maintenance chores and reinforcing them through constant repetition, the company slashed electrical breakdowns by 80% since 1990 and saved millions of dollars." This observation provides yet another example where preventive maintenance contributes to a company’s profitability.

In an anecdotal story, a maintenance technician told one company’s Vice-President of Operations that he considered 80

Certainly, this was one Vice President who knew how to communicate the equipment uptime to the technicians. The value of extending the equipment life by performing proper preventive maintenance was highlighted in an article where it was explained that "Without proper preventive maintenance, the usable life of any piece of equipment is much shorter than its design life, sometimes by as much as 30%." For a company to maximize its return on investment in an asset, it needs to have an effective preventive maintenance program.

Early replacement of expensive assets will force a company to increase its capital appropriations budget. This unnecessary expense detracts from the company’s profitability.

In the facilities sector, energy usage is a large portion of a company’s budget. However, there are large financial impacts that an effective preventive maintenance program can have on energy expenses. For example, consider some statistics for Heating, Ventilation, and Air Conditioning:

• Controls for HVAC that are malfunctioning or simply out of calibration place excessive demands on equipment, causing up to a 20% greater energy demand.
• A condenser surface fouled with 0.015" of scale will increase energy usage by 11%.
• An improperly-tuned boiler will require as much as 25% more fuel to operate.
• A sluggish purge system on a chiller can boost energy consumption by as much as 10%.

If these items are not addressed on a proper preventive maintenance program, the energy consumption is higher than it needs to be (on average by 5% to as much as 10%) for the entire facility or plant.

In another facility example, the following parameters were given:

• 100,000-square-foot building
• 300-ton chiller, 200-hp boiler
• Air volume is 90,000CFM

With this established as a baseline for the size of the facility, the following typical equipment conditions were established:

• Refrigeration condenser are slightly scaled
• Coils and filters in air handlers are dirty
• Purge unit is not fully removing non-condensing gasses
• Controls is not functioning to specifications
• Boiler controls out of trim by 4%
• Cooling tower fans and nozzles are inefficient

All of these conditions are typical when a company does not have a good preventive maintenance program. The results were calculated and it was determined that the facility would be wasting approximately $25,500 per year in energy costs.

Another interesting study, published by the magazine Preventive/Predictive Maintenance Technology, categorized companies into three major classifications. These were:

• In a breakdown mode
• In a preventive mode
• In a predictive mode

After classifying each of the organizations, the installed horsepower for each of the plants was determined. The installed horsepower was then used in the denominator to calculate the maintenance cost (the numerator) per installed horsepower. The results were:

• In a breakdown mode, $17
• In a preventive mode, $11
• In a predictive mode, $7

This clearly shows that the more advanced a company becomes in their maintenance practices, the lower the overall maintenance costs become. While it may seem apparent that the maintenance costs (numerator) was impacted, the installed horsepower (denominator) was also lowered. The reason is the well-maintained and reliable equipment requires less redundancy. For example, the company may only need two compressors at the plant instead of three due to the reliability of the primary compressors.

Furthermore, they may not need a third air compressor because the preventive maintenance program eliminates air leaks, reducing the demand form compressed air.

Finally, one other area of consideration covers the legal ramifications for companies without good preventive maintenance programs. For example, Modern HealthCare’s magazine Facility Operation highlighted an article about hospitals with poor preventive maintenance program. In part, it noted "There are three hospitals with lawsuits filed against them, which had weak or no preventive maintenance programs at all." This statement highlights the fact that good preventive maintenance programs are essential to maintain a good standing in the community, whether a company is a hospital or any industrial type of a plant.

Additional Justification for Preventive Maintenance

Increased automation in industry requires preventive maintenance. The more automated that the equipment is, the more components there are that and fail and cause the entire piece of equipment to be taken out of service. Routine services and adjustments can keep the automated equipment in the proper condition to provide uninterrupted service.

Just-In-Time manufacturing (JIT), which is becoming more common in the United States today, requires that the materials being produced into finished goods arrive at each step of the process just in time to be processed. JIT eliminates unwanted and unnecessary inventory. However, JIT also requires high equipment availability. Equipment must be ready to operate when a production demand is made; it cannot break down during the operating cycle. Without the buffer inventories (and high costs) traditionally found in U.S. processes, preventive maintenance is necessary to prevent equipment downtime. If equipment does fail during an operational cycle, there will be delays in making the product and delivering it to the customer. In these days of intense competitiveness, delays in delivery can result in lost customers. Preventive maintenance is required so that equipment is reliable enough to develop a production schedule that, in turn, is dependable enough to give a customer firm delivery dates.

In many cases, when equipment is not reliable enough to schedule to capacity, companies will purchase another identical piece of equipment. Then if the first one breaks down on a critical order, they have a back-up. With the price of equipment today, however, this back-up can be an expensive solution to a common problem. Unexpected equipment failures can be reduced, if not almost eliminated, by a good preventive maintenance program. With equipment availability at its highest possible level, redundant equipment will not be required.

Reducing insurance inventories has an impact on maintenance and operations. Maintenance carries many spare parts in case the equipment breaks down. Operations carry additional spare parts in process inventory for the same reason. Good preventive maintenance programs allow the maintenance departments to know the condition of the equipment and prevent breakdowns. The savings from reducing (in some cases, eliminating) insurance inventories can often finance the entire preventive maintenance program.

In manufacturing and process operations, each production process is dependent on the previous process. In many manufacturing companies, these processes are divided into cells. Each cell is viewed as a separate process or operation. Furthermore, each cell is dependent on the previous cell for the necessary materials to process. An uptime of 97% might be acceptable for a stand-alone cell. But if ten cells, each with a 97% uptime, are tied together to form a manufacturing process, the total uptime for the process is only 73% (see Figure 1-4).

This level is unacceptable in any process. Preventive maintenance must be used to raise uptime to even higher levels. Performing needed services on the equipment when required leads to longer equipment life. Returning to an earlier example, an automobile that is serviced at prescribed intervals will deliver a long and useful life. However, if it is neglected

Preventive maintenance reduces the energy consumption for the equipment to its lowest possible level. Well-serviced equipment requires less energy to operate because all bearings, mechanical drives, and shaft alignment receive timely attention. By reducing these drains on the energy used by a piece of equipment, overall energy usage in a plant can decrease by 5% to as much as 11%.

Quality is another cost reduction that helps justify a good preventive maintenance program. Higher product quality is a direct result of a good preventive maintenance program. Poor, out-of-tolerance equipment never produces a quality product. World class manufacturing experts recognize that rigid, disciplined preventive maintenance programs produce high quality products. To achieve the quality required to compete in the world markets today, preventive maintenance programs are required. If operations or facilities were organized and operated the way the majority of maintenance organizations are, we would never get any products or services when we needed them. An attitude change is necessary to give maintenance the priority it needs. This change also includes management’s viewpoint. Modern management tends to sacrifice long-term planning for short-term returns. This attitude causes problems for maintenance organizations, leading to reactive maintenance with few or no controls.

When maintenance is given its due attention, it can become a profit center, producing positive, bottom line improvements to the company. No preventive maintenance program will be truly successful without strong support from the facility’s upper management. Many decisions must be made by plant management to allow time to perform maintenance on the equipment instead of running it wide open. Without upper management’s commitment to the program, PM will either never be performed, or it will be performed too little, too late. Thus, management support is the cornerstone for any successful PM program.

Frequency Analysis

Excerpted From Introduction to Machine Vibration by Glenn D. White
(ISBN: 978-0-9820517-4-0)

To get around the limitations in the analysis of the wave form itself, the common practice is to perform frequency analysis, also called spectrum analysis, on the vibration signal. The time domain graph is called the waveform, and the frequency domain graph is called the spectrum. Spectrum analysis is equivalent to transforming the information in the signal from the time domain into the frequency domain. The following relationships hold between time and frequency:

A train schedule shows the equivalence of information in the time and frequency domains:

The frequency representation in this case is much shorter than the time representation. This is a "data reduction".

Note that the information is the same in both domains, but that it is much more compact in the frequency domain. A very long schedule in time has been compressed to two lines in the frequency domain. It is a general rule of the transformation characteristic that events that take place over a long time interval are compressed to specific locations in the frequency domain.

Why perform Frequency Analysis?

In the figure below, note that the individual frequency components are separate and distinct in the spectrum, and that their levels are easily identified. It would be difficult to extract this information from the time domain waveform.

It has been argued that the primary reason for the widespread use of frequency analysis is the wide availability of the inexpensive FFT analyzer!

In the next figure, we see that events that are overlapped and confused in the time domain  are separated into individual components in the frequency domain. The vibration waveform contains a great deal of information that is not apparent to the eye. Some of the information is in very low-level components whose magnitude may be less than the width of the line of the waveform plot. Nevertheless, such very low-level components may be important if they indicate a developing problem such as a bearing fault. The essence of predictive maintenance is the early detection of incipient faults, so we must be sensitive to very small values of vibration signals, as we will see shortly.

In the next figure, a very low-level component represents a small developing fault in a bearing, and it would have been unnoticed in the time domain or in the overall vibration level. Remember that the overall level is simply the RMS level of the vibration waveform over a broad frequency range, and that a small disturbance such as the bearing tone shown here could double or quadruple in level before the overall RMS would be affected.

On the other hand, there are circumstances where the waveform provides more information to the analyst than does the spectrum.

How to perform Frequency Analysis

Before we investigate the procedure of performing spectrum analysis, we will look at the various types of signals we will be working with.

From a theoretical and practical standpoint, it is possible to divide all time domain signals into several groups. These different signal types produce different types of spectra, and to avoid errors in performing frequency analysis, it is instructive to know their characteristics.

Stationary Signals

The first natural division of all signals is into either stationary or non-stationary categories. Stationary signals are constant in their statistical parameters over time. If you look at a stationary signal for a few moments and then wait an hour and look at it again, it would look essentially the same, i.e. its overall level would be about the same and its amplitude distribution and standard deviation would be about the same. Rotating machinery generally produces stationary vibration signals.

Stationary signals are further divided into deterministic and random signals. Random signals are unpredictable in their frequency content and their amplitude level, but they still have relatively uniform statistical characteristics over time. Examples of random signals are rain falling on a roof, jet engine noise, turbulence in pump flow patterns and cavitation.

Deterministic Signals

Deterministic signals are a special class of stationary signals, and they have a relatively constant frequency and level content over a long time period. Deterministic signals are generated by rotating machines, musical instruments, and electronic function generators. They are further divisible into periodic and quasi-periodic signals. Periodic signals have waveforms whose pattern repeats at equal increments of time, whereas quasi-periodic signals have waveforms whose repetition rate varies over time, but still appears to the eye to be periodic. Sometimes, rotating machines will produce quasi-periodic signals, especially belt-driven equipment.

Deterministic signals are probably the most important in vibration analysis and their spectra resemble the following:

Most quasi-periodic signals are actually a combination of several harmonic series.

Periodic signals always produce spectra with discrete frequency components that are a harmonic series. The term "harmonic" comes from music, where harmonics are multiples of the fundamental frequency.

Non-Stationary Signals

Non-stationary signals are divided into continuous and transient types. Examples of non-stationary continuous signals are the vibration produced by a jackhammer and the sound of a fireworks display. Transient signals are defined as signals which start and end at zero level and last a finite amount of time. They may be very short, or quite long. Examples of transient signals are a hammer blow, an airplane flyover noise, or a vibration signature of a machine run up or run down.

Examples of some wave forms and their spectra

Following are some waveforms and spectra that illustrate some important characteristics of frequency analysis. While these are idealized in the sense that they were made from an electronic function generator and analyzed with an FFT analyzer, they do show certain attributes that are commonly seen in machine vibration spectra.

A sine wave consists of a single frequency only, and its spectrum is a single point.

Theoretically, a sine wave exists over infinite time and never changes. The mathematical transform that converts the time domain waveform into the frequency domain is called the Fourier transform, and it compresses all the information in the sine wave over infinite time into one point. The fact that the peak in the spectrum shown above has a finite width is an artifact of the FFT analysis, which will be discussed later.

A machine with imbalance has an excitation force that is a sine wave at 1X, or once per revolution. If the machine were perfectly linear in response, the resulting vibration would be a pure sine wave like the one shown above. In many poorly balanced machines, the waveform does resemble a sine wave, and there is a large vibration peak in the spectrum at 1X, or one order.

Here we see that a harmonic spectrum results from a periodic waveform, in this case a "clipped" sine wave. The spectrum contains equally spaced components, and their spacing is equal to 1 divided by the period of the waveform. The lowest of the components above zero frequency is called the fundamental, and the others are called harmonics. This waveform came from a signal generator, and it can be seen that it is not symmetrical about the zero line. This means it has a "DC." component, and this is seen as the first line at the left in the spectrum. This is to illustrate that a spectrum analysis can go all the way to zero frequency, or in common terminology, to DC.

In vibration analysis of machinery, it is not usually desirable to include such low frequencies in the spectrum analysis for several reasons. Most vibration transducers do not have response to DC, although there are accelerometers that are used in inertial navigation systems that do have DC response. For machine vibration, the lowest frequency that is generally considered of interest is about 0.3 orders. In some machines this will be below 1Hz. Special techniques are required to measure and interpret signals below this frequency.

Note that because this spectrum consists of discrete points, the signal is by definition deterministic!

It is not uncommon in machine vibration signatures to see a waveform which is clipped something like the one shown above. What this usually means is there is looseness in the machine, and something is restricting its motion in one direction.

The signal shown above is similar to the previous one, but it is clipped on both positive and negative sides, resulting in a symmetrical waveform. This type of signal can occur in machine vibration if there is looseness in the machine and motion is restricted in both directions. The spectrum seems to have harmonics, but they are actually only the odd-numbered harmonics. All the even-numbered harmonics are missing. Any periodic waveform that is symmetrical will have a spectrum with only odd harmonics! The spectrum of a square wave would also look like this.

Sometimes the vibration spectrum of a machine will resemble this if there is extreme looseness and the motion of the vibrating part is restricted at each extreme of displacement. An unbalanced machine with a loose hold-down bolt is an example of this.

Shown above is a short impulse produced by a signal generator. Note that its spectrum is continuous rather than discrete. In other words, the energy in the spectrum is spread out continuously over a range of frequencies rather than being concentrated only at specific frequencies. This is characteristic of non-deterministic signals such as random noise and transients. Note that the level of the spectrum goes to zero at a particular frequency. This frequency is the reciprocal of the length of the impulse, therefore the shorter the impulse, the greater its high frequency content. If the impulse were infinitely short (the so-called delta function, in mathematics), then its spectrum would extend from 0 to infinity in frequency.

By examining a continuous spectrum, it is usually impossible to tell whether it is the result of a random signal or a transient. This is an inherent limitation of Fourier-type frequency analysis, and for this reason it is a good idea to look at the wave form when a continuous spectrum is encountered. As far as machine vibration is concerned, it is of interest to the analyst whether impacting is occurring (causing impulses in the wave form) or random noise (for example, from cavitation) exists in the signal.

A rotating machine seldom produces a single impulse like this, but in the "bump test", this type of excitation is applied to the machine. Its vibration response will not be a classic smooth curve like this one, but it will be continuous with peaks corresponding to the natural frequencies of the machine structure. This spectrum shows that the impulse is a good input force to use in this type of test, for it contains energy over a continuous frequency range.

If the same impulse that produced the previous spectrum is repeated at a constant rate, the resulting spectrum will have an overall envelope with the same shape as the spectrum of the single impulse, but it will consist of harmonics of the pulse repetition frequency rather than a continuous spectrum.

A bearing produces this type of signal with a definite defect in one of the races. The impulses can be very narrow, and they will always produce an extensive series of harmonics.

Modulation Effects

Modulation is a non-linear effect in which several signals interact with one another to produce new signals with frequencies not present in the original signals. Modulation effects are the bane of the audio engineer, for they produce "intermodulation distortion", which is annoying to the music listener. There are many forms of modulation, including frequency and amplitude modulation, and the subject is quite complex. We will now look at the two primary types of modulation individually.

It is rare to see frequency modulation by itself; most machines will produce amplitude modulation at the same time as frequency modulation!

Frequency modulation (FM) is the varying in frequency of one signal by the influence of another signal, usually of lower frequency. The frequency being modulated is called the "carrier". In the spectrum shown above, the largest component is the carrier, and the other components which look like harmonics, are called "sidebands". These sidebands are symmetrically located on either side of the carrier, and their spacing is equal to the modulating frequency.

Frequency modulation occurs in machine vibration spectra, especially in gearboxes where the gear mesh frequency is modulated by the rpm of the gear. It also occurs in some sound system loudspeakers, where it is called FM distortion, although it is generally at a very low level.

This example shows amplitude modulation at about 50% of full modulation

Notice that the frequency of the waveform seems to be constant and that it is fluctuating up and down in level at a constant rate. This test signal was produced by rapidly varying the gain control on a function generator while recording the signal.

This type of signal is often produced by defective bearings and gears, and can be easily identified by the sidebands in the spectrum.

The spectrum has a peak at the frequency of the carrier, and two more components on each side. These extra components are the sidebands. Note that there are only two sidebands here compared to the great number produced by frequency modulation. The sidebands are spaced away from the carrier at the frequency of the modulating signal, in this case at the frequency at which the control knob was wiggled. In this example, the modulating frequency is much lower than the modulated or carrier frequency, but the two frequencies are often close together in practical situations. Also these frequencies are sine waves, but in practice, both the modulated and modulating signals are often complex. For instance, the transmitted signal from an AM radio station contains a high-frequency carrier, and many sidebands resulting from the carrier modulation by the voice or music signal being broadcast.

A vibration and acoustic signature similar to this is frequently produced by electric motors with rotor bar problems.

It is almost impossible to tell beating from amplitude modulation by looking at the waveform, but they are fundamentally different processes, caused by different phenomena in machines. The spectrum tells the story.

This waveform looks like amplitude modulation, but is actually just two sine wave signals added together to form beats. Because the signals are slightly different in frequency, their relative phase varies from zero to 360 degrees, and this means the combined amplitude varies due to reinforcement and partial cancellation. The spectrum shows the frequency and amplitude of each component, and there are no sidebands present. In this example, the amplitudes of the two beating signals are different, causing incomplete cancellation at the null points between the maxima. Beating is a linear process -- no additional frequency components are created.

Electric motors often produce sound and vibration signatures that resemble beating, where the beat rate is at twice the slip frequency. This is not actually beating, but is in fact amplitude modulation of the vibration signature at twice the slip frequency. Probably it has been called beating because it sounds somewhat like the beats present in the sound of an out of tune musical instrument.

The following example of beats shows the combined waveform when the two beating signals  are the same amplitude. At first glance, this looks like 100% amplitude modulation, but close inspection of the minimum amplitude area shows that the phase is reversed at that point.

This looks like 100% amplitude modulation!

This example of beats is like the previous one, but the levels of the two signals are the same, and they cancel completely at the nulls. This complete cancellation is quite rare in actual signals encountered in rotating equipment.

Earlier we learned that beats and amplitude modulation produce similar waveforms. This is true, but there is a subtle difference. These waveforms are enlarged for clarity. Note that in the case of beats, there is a phase change at the point where cancellation is complete.