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Cut the FLAB from Your Maintenance Program

Drew D. Troyer, CRE, CMRP

At the New Year, most of us to resolve to make changes for the better in our lives.  Frequently, these changes center around improving our health by exercising more, eating more healthfully and making other lifestyle changes with a focus on cutting some flab.  What about our resolution for plant and equipment maintenance?  Here too, we need to cut the FLAB – but in this case, FLAB is an acronym that pertains to problems with Fasteners, Lubrication, Alignment and Balance – the proactive elements of equipment care.  This year, let’s resolve to improve equipment health by earnestly resolving ourselves to cut the FLAB.  In this article, will discuss the what, why and how for doing just that.  For now, we’re focusing on mechanical health and sources of mechanical failure.  In a future article, I’ll address the electrical ramifications of FLAB management.

When operating properly, machines maintain a dynamic balance between the operating forces attempting to produce surface to surface contact and wear in our equipment and the opposing forces attempting to separate those surfaces.  Depending upon the application, the operating forces can range from hundreds of pounds to hundreds of thousands of pounds per square centimeter depending upon whether the contacts are sliding or rolling nature.  Opposing forces are the hydrodynamic or elasto-hydrodynamic film produces by the lubricant.  When conditions are properly maintained, full film-lubricated equipment, such as journal and rolling elements bearings will run trouble-free for a very long time.  In fact, in the ISO standard for calculating rolling element bearing life the equation resolves to infinity when conditions are perfectly maintained.  However, when operating forces become too strong and or hydrodynamic and/or elesto-hydrodynamic lubricant film is weakened, the expected life of the component drops precipitously due to surface to surface contact and the associated abrasive, fatigue and/or adhesive wear that results. What do you get for your toils and effort to maintain FLAB in your equipment?  If you’re lucky, a five-micron film of separation.  Yep, it’s a lubricant film that’s about the diameter of a red blood cell that differentiates between reliability and ruin in your equipment.  That’s not much of a margin for error.

The most common causes of increasing forces that lead to wear appear to us in the form of vibration.  Machines can vibrate for a lot of reasons.  In some instances, they vibrate because machine surfaces have been sufficiently disfigured that the analyst sees defects, which indicates the component has reached the end of its life.  Commonly, however, there are precursor vibrations that indicate FLAB in our maintenance program.  These “tramp” forces caused by vibration significantly shorten the life of our machines.  Figure 1 illustrates the relationship between applied versus rated force and the corresponding predicted life for a rolling element bearing.  Let’s explore the FLAB-related root causes of vibration that lead to failure.

 

flab_fig1
Figure 1 - Vibration introduces "tramp" forces that rob machines of their useful life.

Fasteners

Fasteners are often overlooked in the world of proactive and precision maintenance.  Few maintainers have received even basic training on fasteners and how they function.  There are a lot of misconceptions about how fasteners actually achieve the required clamping force, through the material elasticity in the threads, with which to hold equipment together, the effectiveness of lock-washers, the roll of lubricants, etc.  And, sadly, torque wrenches are a rare sight in the maintainer’s tool box.  Here are some common mistakes I see on the plant floor related to fastener management:

  1. Lack of torqueing standards in common maintenance work instructions.  Simply stated, we must provide clear instructions about the size and type of nuts, bolts and washers to be used.  We must also specify required torque value, lubrication instructions, bolt sequence and any special instructions for tightening down equipment.  Take a survey of your work instructions to determine if you’re providing clear instructions to your maintainers.
  2. Use of undersized fasteners.  I see this commonly on conveyer systems.  Undersized nuts and bolts lack the required surface area around the slots to achieve the required clamping force to secure the equipment.  A common sight is flat washers that are bent down into the slot.  When this occurs, your flat washer is functioning as a spring and significantly reducing the clamping force, which in turn allows the fasteners to vibrate loose.
  3. Loose or missing fasteners.  This is a tell-tale that the organization does not conduct routine fastener audits to verify the presence, proper condition and proper torque value of fasteners in place.  These audits should be routine proactive PMs performed at least once yearly – more frequent in aggressive vibratory or environmental conditions.
  4. No torque wrenches.  As previously noted, torque wrenches are a rare site on the plant floor.  Mechanics should be issued an appropriate set of standard torque wrenches for day-to-day use and specialty wrenches (such as high torque hydraulic or pneumatic wrenches) must be available.  All torque wrenches must be properly maintained.  In addition to fastening during assembly, torque wrenches are required for routine torque audits and tightening PMs.  Specialty torque measurement devices are also available and very useful.
  5. Improper foundation and shimming.  Shims are designed to correct for incongruities between the mating surface of the machine and the foundation.  In some cases machines are shimmed with material that’s too compressible and in other cases, shims are simply not applied properly.  In other cases, the mating surfaces are simply to “untrue” to shim, usually indicating problems with the foundation.  Another problem can be the foundation to which the equipment is attached itself, which simply allows too much movement.  For example, overhung equipment, when it’s mounted to a flimsy structure will vibrate.  Sometimes this is intentional, when the designer wants forces to relive to the structure with flexibility.  In other instances, it’s just poor design. Poorly laid concrete foundations, for example may have too much undulation, poorly mixed concrete or improperly secured bolts.

Alignment

So, we’re skipping the L in our flab acronym for a moment and moving to alignment, the second force in the FLAB equation that produces vibration.  Never, fear, however, we’ll circle back to pick up lubrication. Whether it is shafts and couplings or belts and sheaves, misalignment produces very aggressive and deleterious forces that typically show up as vibration at two-times the running speed frequency.  Angular, offset and combination misalignment forces can very rapidly wear out couplings, belts and bearings.  I recently spent a week in a mine filled with sensory experiences – squealing belts and the heady aroma of burning rubber.  This makes belt maintenance a constant nuisance and bearing failure, and the associated downtime, an all-to-common event.  Here are some common problems I see with misalignment on the plant floor.

  1. Lack of precision in alignment work instructions.  As is the case with fastener management, our maintenance work instructions typically don’t provide the specific fits, tolerances, quantity and quality details to guide the craftsperson through the process of achieving proper alignment of shafts and sheaves. Precision shaft alignment is typically defined as a function of speed.  At 3600 rpm, allow no more than 0.3 mils/inch of angular and 1.0 mils of offset misalignment. At 1800 rpm, allow no more than 0.5 mils/ inch of angular and 2.0 mils of offset misalignment. At 900 rpm, allow for no more than 1.0 mils/inch of angular and 4.0 mils of offset misalignment.
  2. Sloppy pipework.  If you require a hoist to pull pipe work into position for fastening, you’re producing misalignment forces.  Pipework has become increasingly shoddy over the past 20 plus years that I’ve been a practicing reliability engineer.  I’m sure your fathers and grandfathers gave you the same advice that mine gave me: “measure twice, cut once.”  This absolutely applies to pipework.  And when the pipework is intricate, spend the extra few dollars to employ qualified pipefitters who know how to properly size and fit piping while considering thermal growth, expected dynamic forces, etc.
  3. Failure to properly consider thermal growth.  Different materials have different coefficients of thermal expansion.  Failure to properly consider this leads to binding and misalignment.  Thermal expansion values should be incorporated into the work instructions and they should be customized for each piece of equipment.  Don’t rely on maintainers to remember all the numbers or have the luxury of time to do the calculations on the spot – even if they know how to do so.  They’re usually under the gun to get the equipment fixed and back up and running, which forces them to make approximations that compromise our efforts to achieve precision proactive control of machine health.   
  4. Too much reliance of flexible couplings.  Flexible couplings, such as spider couplings and belts, allow for more misalignment than rigid couplings.  Is this really an excuse to be lazy and imprecise with alignments?  Hell no.  Firstly, flexible couplings only divert some of the misalignment force from the machine components to the coupling.  Secondly, it makes couplings a high maintenance item.  Your production manager, and moreover, your customers, don’t care whether your machines are down due to a bearing failure or a coupling failure – you’re still down. Apply the same precision when aligning equipment with flexible coupled equipment that you would when aligning rigid coupled equipment.  Treat the flexible coupling as an insurance policy to protect against that which you can’t control – such as significant or unusual changes in temperature or the odd fastener problem.  Don’t make the flexible coupling your first line of defense – that’s just lazy.
  5. Failure to use precision methods.  In a crew of nine men and a supervisor, usually one man and the supervisor can do a highly precise job of aligning with dial indicators.  Once in a while, we run across that special maintainer – the “machine whisperer” who can precisely align a machine with a straight edge and gut-feel.  Do you want to manage the reliability of your equipment with one in 10 or one in 100 odds?  I don’t.  Get with the program – get laser alignment equipment for shafts and sheaves, keep it in good working order and train your people on how to use it properly.

Balance

The third common source of abnormal, vibration induced force is unbalance.  Unbalance occurs when there is a mass distribution inequity in a rotating machine that produces relative centrifugal force (RCF).  The amount of RCF is a function of the weight of the mass imbalance (e.g. in grams), its distance from the rotating centerline and the rotational speed.  The increase in RCF is linearly related to the weight of the mass imbalance and its distance from the rotating centerline and geometrically related to the rotational speed.  In other words, high speed equipment is particularly sensitive to unbalance.  As with fastener induced looseness and misalignment, unbalance increase the force on contacting surfaces, thus increasing the likelihood of surface-to-surface contact and wear by overwhelming the protective film provided by the lubricant. Unbalance is typically observed at one-times running speed in the vibration spectra.  Here are some common problems I see on the plant floor.

  1. Failure to shop balance equipment during rebuild.  Unless you’re pumping abrasive slurry, where impeller wear is the dominant failure mode, all pumps should be shop balanced during rebuild.  The ISO 1940 standard calls for balancing to G6.3 precision for pumps, fans and other balance of plant equipment.  I prefer balancing to G2.5 and preferably G1.0 or better for this equipment. I’m candidly surprised how rarely this simple process of shop balancing is employed in plant shops.  In most instances, low speed dynamic balancing works fine for process pumps and other balance of plant equipment.  High-speed or at-speed balancing is only required for high value critical turbo-machinery.  Low speed dynamic balancing is relatively easy and inexpensive to conduct.  It requires some skill, but it’s not that hard.  I’m mystified by the fact very few organizations do it.
  2. Failure to incorporate balance standards into your contracts.  We routinely send electric motors and other rotating equipment out for rewind or rebuild.  Do our contracts require the shops to dynamically balance the equipment?  Typically not.  There are reasons why rebuilt equipment doesn’t typically last as long as new equipment – lack of precision balance is one of the big ones.  And, as is the case for pumps that are rebuilt on-site, low speed dynamic balancing is typically sufficient for most electric motors, so the process is pretty easy and inexpensive.  Again, I prefer standards set to G2.5, G1.0 or better.
  3. Failure to manage dynamic balancing in fans.  Whether it’s a rebuild in the shop or routine maintenance in the plant, we must pay special attention to fans.  Fan blades commonly extend well out from the rotating centerline. Because RCF increases geometrically the further the mass imbalance is from the centerline, we really have to pay attention to fans.  Moreover, fans are susceptible to wear and corrosion, especially at the tips, and accumulation of debris, which introduces unbalance forces.  Fortunately, fans are easy to balance in the field by adding (or occasionally removing) mass. 
  4. The unbalance cure creates other problems. In some applications, we must periodically wash down fans to clear away accumulated debris and restore balance.  This is commonly done with water spray directed at the fan blades.  Exercise caution when cleaning fans, as the water spray has been known to migrate past labyrinth seals and into bearings.  It’s not a good bargain to trade an unbalanced fan for water contaminated grease or oil.  If the risk is high, take precautions by using deflectors, greasing before and after cleaning, putting a bead of grease around the exterior of the labyrinth or, in the case of oil lubricated fans, change the oil or, better yet, use a filter cart with water removing elements to decontaminate the oil during and after the wash down.

Lubrication

Thus far we’ve talked about the imposing vibration inducing forces that squeeze component surfaces together to cause contact, wear and failure.  The lubricant represents the sole impeding force to prevent that from occurring. Sometimes called the “life blood” of the machine, the lubricant must provide the dynamic separation of machine surfaces – the blood cell-sized film - to protect your machines against the normal dynamic forces of operation. And when vibration is allowed to get out of hand due to poor management of fasteners, alignment and balance, the warrior is overwhelmed and failure ensues.  Here are some common problems I see on the plant floor.

  1. Wrong viscosity or viscosity index.  If the viscosity is too low, the lubricant can’t develop sufficient film thickness to separate component surfaces.  If the viscosity is too high, it may not flow into the clearance areas easily enough or be sufficiently splashed or slung to the points where it is required.  One can’t determine the required viscosity without considering the operating temperature, since temperature has such a great influence on viscosity.  When temperature fluctuates significantly, the application requires a high viscosity index fluid.  Viscosity index is a dimensionless number that indicates how much viscosity changes for a given change in temperature.  A high viscosity index increases the temperature range in which the lubricant is suitable.  A common mistake in the plant is to overlook the viscosity of the base oil in grease.  Viscosity is the most important property of the lubricant, make sure you get it right for both oil and grease lubricated applications.
  2. Wrong additive package.  Ideally, the machine develops a full-film separation between moving surfaces – hydrodynamic for sliding contacts and elasto-hydrodynamic for rolling contacts.  However, in some instances due to high loads, frequent starts and stops, load and speed variations, etc., full-film lubrication can’t be achieved.  In these instances, the lubricant must be formulated with an anti-wear (AW) or extreme pressure (EP) additive to protect the machine under boundary contact conditions.  These additives don’t eliminate wear, but rather reduce it through a mild chemical corrosion intervention.  Other operational and/or environmental conditions may warrant other additives to modify the performance properties of the lubricant.  These might include detergents, dispersants, viscosity index improvers, pour point depressants, tackifiers, etc.
  3. Wrong lubrication interval.  Too many plants just guess at the right interval for greasing or performing oil changes.  An oil change is a downtime task that introduces a lot of risk to the system.  We may not use the right lubricant.  We may not reestablish the correct level.  Valves may be left open and breather and fill caps may be left off.  We may introduce contamination during the process.  The list goes on.  Employ oil analysis to either change the oil on condition or to establish and appropriate change interval through experimentation.  Sometimes, oil is changed with the intent of decontaminating.  Usually, the machine is shut down for some period of time prior to draining, which allows the dirt, water, sludge and other debris to settle to the bottom – rendering the oil change futile as a decontamination tool.  Instead of changing the oil, consider offline filtration when the machine is running where appropriate or while it’s shut down in other cases.  If the goal is to decontaminate, then make sure your PMs are effective.  Greasing is another area where entirely too much guesswork is applied.  Fortunately, formulas exist for estimating the appropriate greasing interval, which consider the machine, the application and the environment.  For some applications, ultrasonic instruments can add an extra degree of precision.
  4. Wrong lubrication volume.  Occasionally, we see oil lubricated systems that lack a level indicator.  This is really an unacceptable oversight.  We must be able to check the level of all lubricated machines.  Ideally, the mechanism is non-invasive (e.g. no dipsticks) and indicates the acceptable level when the machine is running and when it’s down.  Much more common is lack of detail in PMs to instruct lubrication techs how much grease to apply.  This is such a widespread and easily controlled problem that I continue to be mystified as to why it’s not taken more seriously.  Over and under greasing are primary root causes of electric motor failure – we see it again and again – PMs that simply say “grease the motor” without clearly stating what kind of grease and how much to apply to the drive and non-drive ends (yes, it’s commonly different).  We must clearly define the volume of grease to be applied to each lubricant point in our lube routes – the formulas area easy, but it takes some work to gather the input information.  As is the case with precision fastening, alignment and balance, precision lubrication requires a clear definition of the quantity and quality details.
  5. In sufficient contamination control.  Rivaling lack of precision in quantifying how much grease to apply to each point is a lack of precision on controlling contamination, which prohibits thee lubricant from doing its job.  A contaminant is anything that’s in the lubricant but shouldn’t be.  Water and particles are the most common, so we’ll look at them and their effects in more detail.
    1. Water contamination.  An obvious risk of water contamination is rust and corrosion on metal surfaces.  Less obvious is hydrolysis.  Water contamination reacts with many lubricant additives, reducing their effectiveness and, in some cases, producing hydrogen sulfide and sulfuric acid.  Water also reacts with metals to produce oxidizing agents that attack the base oil.  Even less obvious, and potentially more deleterious, is how water affects the lubricant’s film strength.  As previously discussed, viscosity is the lubricants most important property because it determines film thickness.  Oil possesses a physical property whereby viscosity increases as a function of pressure.  The higher the load, the higher the viscosity and the film thickness.  Water does not possess this same physical property, so when it’s present, the viscosity-pressure relationship in the oil is compromised, which decreases film strength and increases the likelihood of surface to surface contact. Water is particularly damaging in rolling contacts, where the load forces are very high – in the hundreds of thousands of pounds per square inch.  Rolling element bearings, for example, depend on the viscosity-pressure relationship in oil to protect components.  Water contamination can increase wear rates by as much as 40 times.  Target levels for moisture should range between 100 and 300 ppm or better for most applications. Except for rare cases, water contamination should never be allowed to exceed 500 ppm.
    2. Particle contamination.  The lubricant provides a blood cell-sized separation between moving surfaces. If it’s not present in contacts that are in relative sliding motion, surface to surface contact and abrasion (two-body) occur.  In rolling contacts, the lack of a lubrication film results in surface fatigue.  When clearance-sized and larger particles are present in sliding contacts, abrasion (three-body) occurs even when there is film separation.  The particles in oil and grease act like the bits of grit on sandpaper to wear away surfaces.  In rolling contacts, the process is somewhat more complex.  Rolling contacts (e.g. rolling element bearings) transfer load via very small point or line contacts.  The momentary load is extremely concentrated – in the hundreds of thousands of pounds per square inch – and the lubricant film - is very small – rarely exceeding half the diameter of a red blood cell.  A hard particle can bridge the gap provided by the lubricant film and transfer the load to the component surfaces, often concentrating it further.  If a 250,000 psi normal load is transferred via a particle to an area one-tenth the normal area, the resulting load is 2.5 Million psi.  This extreme load typically exceeds the fatigue limit of the metal and produces subsurface cracking.  Over time, the cracks propagate (grow) to the surface and the damage material is released.  This is called pitting wear.  The surrounding material is damaged and dented and overtime may lift away from the surface – a wear mechanism called spalling.  Particles are involved in an estimated 80-90% of all wear, though other forcing functions like vibration, water contamination and insufficient lubrication contribute and influence the rate at which this occurs. For most applications, cleanliness should be maintained to ISO 4406 15/12/9 to 19/16/13, depending upon the criticality of the application and the machine’s sensitivity to particle contamination.  Contamination should never be allowed to exceed ISO 4406 21/18/15.
  6. Incompatible grease thickeners. Unique to grease is the thickener.  These thickeners are frequently incompatible with one another.  A very common problem is the failure to define the grease used in the initial charge at the motor factory or rebuild shop.  If the factory or rebuild shop employ a polyurea thickened grease, for example, and the plant uses lithium complex thickened grease for routine lubrication PMs, you have a probable compatibility issue on your hand.  The incompatible thickeners will react, soften and separate, causing the grease to leak out and/or for thickener, which provides no lubrication in the component contact zones, to cake up and harden, which prevents new grease from making its way into the components.

How to Realize Your New Year’s Resolution to Cut the FLAB from Maintenance 

Now that you know what FLAB is and how managing it can make the difference between reliability and ruin, you need a game plan for controlling it.  Here is yourFIVE STEP PROCESSfor putting FLAB under control in your plant.

  1. Make FLAB Management a Priority. We always seem to have the time and money to repair broken equipment, but we can’t find the time and money to keep it from getting broken.  Just like we always find the time and money to get that triple bypass to avoid a heart attack, but we can’t seem to make it out for a jog or to the gym to prevent it from happening.  Until your organization makes proactive and precision management of FLAB a priority, you’ll remain in the cycle of despair fighting fires.  The best way to get the organization on board is to show them the money.  We have well-researched techniques at our disposal to estimate how much poor FLAB management is costing your organization in economic terms.  Let us help you put a dollar figure on your opportunity so you can get to the starting line and the ball rolling.
  2. Document Your Corrective and Preventive Maintenance Plans. You may think you have documented your maintenance work plans, but if you’re sending a craftsperson to rebuild, install or PM a machine with vague work instructions that fail to define the fit, tolerance, quantity and quality details associated with completing the work, you’re relying on “tribal knowledge” and wishful thinking (e.g. “check fasteners,” “grease motor,” etc.).  One need only look at reliability critical maintenance organizations to get a compass reading – nothing is left to chance in commercial aviation management.  Easy to use tools exist for standardizing work templates whilst allowing for the insertion variable inputs for the fit, tolerance, quality and quantity details associated with FLAB management.  While these tools don’t eliminate all the legwork associated with properly documenting your maintenance work, they certainly make the process much more achievable and manageable.  Because these tools are database driven, you can take advantage of equipment and application duplicates to shorten and expand your standard work practices across other plants and the entire enterprise.  Let us help you put these powerful tools and techniques to work in your organization (figure 2).
  3. Inspect to for Success. The most reliable organizations rely upon inspections and monitoring to drive maintenance decisions.  Don’t limit the process to just finding broken equipment.  Sensory and instrument-based inspections must be FLAB focused.  Remember, big problems are the cumulative effect of small problems that we didn’t address when we should have.  Inspections will detect minor conditional failures such as contaminated lubricants.  However, correcting conditional failures before they become equipment failures must be a priority within the organization.  While instruments, like vibration data collectors, oil analyzers, etc., play a roll, don’t underestimate the power of the “eyometer.”  Sensory inspections should serve as the foundation of your FLAB management process [note: process, not program].  Let us show you how to create an “inspect-to-work” process in place in your plant that focuses on managing FLAB (figure 2).
  4. Train and Tool Your Team. We need smart, educated maintainers and technicians who understand the physics of failure, why FLAB management is critical to equipment life extension and reliability and what they need to do to control them.  Fortunately, this education is readily available and the concepts are relatively simple.  One needn’t be a degreed engineer or physicist to manage FLAB effectively.  Most of the concepts are intuitive and easy to understand.  We must also tool up for FLAB management – torque wrenches, shaft and sheave alignment tools, balancing tools, grease guns with flow meters, vibration, ultrasonic, thermometric/thermographic and lubricant analysis tools.  We must also tool up our machines for proactive control and run-time maintainability (breathers, filters, inspection access hatches, quick couplings, etc.).   As with training for our maintainers, the tools and bits for modifying equipment are readily available and fairly inexpensive.  Let us help you define your training and tooling requirements to achieve proactive and precision management of your FLAB (figure 2).
  5. Measure and Reward on Leading Indicators. Step five competes with step one as the most important.  Step one gets you to the starting line.  Step five, measurement and reward, gets you to the finish line.  Without these two crucial steps in place, steps two thru five can become an exercise in futility.  In 20 plus years as a reliability engineer, I’ve observed that we get exactly what we pay for – unreliability and failure.  We reward our teams for fixing broken equipment with overtime and recognition.  Proactive efforts to keep equipment from breaking go unnoticed and unrewarded.  One need only look to our metrics for answers as to why this is the case.  Most organization are heaving with lagging metrics such as downtime, cost per ton, etc.  We’re always looking in the rear view mirror and rewarding our teams accordingly, which, unfortunately, makes the reactive maintenance culture “autocatalytic.”  We need simple, easy to understand metrics that drive proactive behaviors.  I like overall vibration effectiveness (OVE) and overall lubrication effectiveness (OLE) for cutting the FLAB in the plant.  OVE is simple – it’s the percent of machines that are in compliance for balance multiplied by the percent of machines that are in compliance for alignment multiplied by the percent of machines that are in compliance on tightness.  OLE is simple too – it’s the percent of scheduled lube PMs that were completed on time multiplied by the percent of machines that are in compliance on contamination targets times the percent of machines that are in compliance for lube health targets.  These are leading metrics that are easy to deploy and will drive proactive behaviors if used properly.  Increasing OVE and OLE increases reliability, by definition.  Increasing reliability increases availability, by definition.  Increasing availability increases Overall Equipment Effectiveness (OEE), by definition.  Increasing OEE puts you in the best possible position to increase profits and Return on Net Assets (RONA) to make hay while the sun shines and to successfully navigate and survive market downturns.  Let us help you set your metrics and reward systems straight, to focus on the proactive and precision behaviors required to manage the FLAB in your plant.

 

 flab_fig2

Figure 2 - After getting buy-in, follow this process to manage FLAB in your plant.  Don't forget the measure and reward proactive behaviors.


Drew Troyer is president of Sigma-Relilability Solutions.
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