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Maintenance departments throughout the world have undergone radical changes over the last ten years in how they perform maintenance on plant equipment. In most cases, those changes have not led to significant improvements. Many plants have rushed into using the latest technologies at enormous expense, expecting immediate returns on their investment. This has not happened. Why has this technology not produced what it was supposed to do? Basically, the technology that is currently available is superb and, if used correctly, will contribute enormously to the reliable operation and maintenance of machines. Unfortunately, the transition from the analyses to the "hands-on" part of the job leaves much to be desired. This is due in part to the lack of skilled journeymen in the work force.

Invest in the future with training
As companies focus on equipment reliability, capacity, availability, and plant maintenance as a means of improving performance and productivity, the training of maintenance personnel often becomes a much-overlooked investment. Training is expected to be a handmedown from one person to another as was the case when a journeyman had an apprentice. Often, a trainee (apprentice) is shared between two or more journeymen. Unfortunately, this exposes the trainee to many bad habits as he or she works with different people who have different ways of working and different levels of skills and knowledge.

Training must be rigorously controlled to ensure that trainees are assigned to the best journeymen for at least one year, during which time they should have minimum exposure to other journeymen. Bad habits are very difficult to break and can lead to poor maintenance with costly consequences.

Get to know your equipment
To benefit from these new technologies, we must first acquire an understanding of how machines and their components work. Without this knowledge, the analyst/technician has no direction and the fault diagnosis may be inaccurate. The technician should be able to identify each component in a machine, explain its function, and mate the component to its signature in a vibration spectrum. Many analysts have been called to task when they say there is a shaft misalignment but cannot demonstrate how to physically correct it. When this happens, their credibility is lost.

Ideally, an analyst should also be a technician who has had hands-on experience in operating and maintaining machines. Unfortunately, industry now has too many "certified" analysts who can pass tests are still very inexperienced in the art of machinery maintenance.

The Vibration Institute has stated that 60 percent of the people taking Level l certification pass the examination. The failure rate is directly attributed to a lack of practical experience in the field. This situation can only improve if companies are prepared to put the horse in front of the cart again. Practical skills training must be considered as the first step in preparing technicians and analysts to fully understand machinery basics in the areas of plant operations and maintenance.

The evolution of maintenance
Maintenance has evolved over the years from a pure reactive mode to preventive maintenance to a proactive mode.

Reactive maintenance was very costly because:
" We had no control over breakdowns.
" Large inventories of spares had to be maintained.
" The costs of call-outs were all added expenses. 

Preventive maintenance was better than reactive maintenance because it was based on times of expected failures but was still costly for some of the same reasons that reactive maintenance was costly. It still required a large inventory of spare parts, and materials and components were being changed out when there was still a lot of useful life left in them.

Preventive maintenance is still very complimentary to predictive or proactive maintenance because oil and air filters still have to be changed and oil and water levels still have to be maintained in order to keep machines running well.

Blending old skills with new technologies
We, at Strategic Work Systems, have developed an effective precision maintenance program, designed to enhance existing proactive maintenance programs. This program encompasses techniques that have been in use for many years, but these skills have gradually been forgotten because of the attrition of master craftspeople through retirement and natural causes. These forgotten skills work very favorably with the new precision maintenance techniques.

There are quite a number of predictive maintenance technologies available on the market today, with each one bringing its own specialized characteristics to the field of precision maintenance. The most commonly used programs are:
" Vibration analysis
" Infrared thermography
" Ultrasonics
" Lube oil analysis 

These programs are used to anticipate any deterioration from design parameters specified by the equipment manufacturers. Because most machines are part of an overall mechanical system, vibration analysis is the most common diagnostic tool and is the major component of precision maintenance programs. But vibration analysis does not supply all of the information that is necessary for the implementation of a complete precision maintenance program.

Therefore, as a minimum requirement, a lube oil analysis program should support the vibration analysis program. A certified laboratory can analyze samples of lube oil and deliver a report that accurately shows which materials in bearings or in the oil are degrading and the rate of deterioration. If the lube oil is sampled on a monthly basis, the lab report will provide a database for the machine over a six-month period. This is an integral service that the laboratories include in their analysis reports and usually show the last five or six analyses taken on that bearing. A good analyst/technician should be able to take that information and compare it against a vibration spectrum obtained from the same bearing or machine. If the results are plotted together, the plots will run alongside each other like railroad tracks, and as the condition deteriorates, both plots will signal an alert and alarm almost at the same time.

However, if the analyst/technician does not know the composition of Babbitt metal that is used on sleeve bearings, then the high lead, tin and copper levels will not mean very much and consequently will not prevent the failure of the bearing. Likewise, if the viscosity and flash point of the oil relationship is not fully understood, the bearing will fail. In the case of a diesel engine, this ignorance can lead to a crankcase explosion that could injure or kill someone. Clearly, the analyst/technician must have some theoretical skills beyond their basic practical skills.

Building a good lubrication program
The three lubrication requirements that a good program must have are:

1.The lubricant must not be exposed to contaminants. Most component failures can be directly attributed to this avoidable problem.

2.Lubricants must perform despite the presence of some contaminants.

3.Lubricant consumption should be minimized to:
* Prevent spoilage
* Promote safe working conditions
* Ease the burden of spent lubricant disposal
* Promote longer antifriction bearing life 

Furthermore, todays industrial economy requires lubricants to reduce energy consumption whenever possible. The analyst/technician has the resources available to determine the correct amount of lubricant to correctly grease antifriction bearings. Bearings can be correctly greased by the use of a vibration analyzer, an ultrasonic leak detector, or by simply ensuring that the bearings cavity drain plug is removed during the greasing and is replaced approximately 30 minutes after the grease insertion has stopped. Overgreasing motor bearings has reached epidemic proportions and is responsible for approximately 80% of motor burnouts.

Precision maintenance, if practiced correctly, is a commonsense approach to avoiding and resolving problems before they become disasters. This is where the analyst/technician has to have in-depth field experience in all aspects of machinery operation and maintenance. If a disastrous breakdown occurs, the analyst/technician will be called upon to provide information in a rootcause failure analysis investigation. Based on the quality of data and actions taken up to the point of failure, the proactive maintenance program will be justified or condemned. Without experienced people running the program, such a scenario can be disastrous.

The analyst as doctor: Are you misdiagnosing?
When diagnosing problems, it is also helpful to know how pumps and their components work. One common pumping problem that baffles people is cavitationor is it recirculation? These are two very distinct problems, but both share the same characteristic noise and destructive internal erosion that can tear impellers and casings apart.

Cavitation occurs in the lowpressure suction side of the pump and, contrary to certain beliefs, it does not show vane pass frequencies on the vibration analysis spectrum (see Figure 1). Cavitation happens when the fluid is vaporized within the suction line and low-pressure side of the impeller.

This phenomenon occurs when there is insufficient net positive suction pressure, or the saturation temperature of the fluid is higher than its corresponding pressure. As a result, vapor pockets form within the fluid. As the vapor pockets reach the surface of the impeller or casing, the higher fluid pressure causes the pockets to collapse, which creates noise, vibration, and possible structural damage to the pump (specifically on the suction side of the impeller and casing). 

Figure 1: Spectra showing cavitation

Recirculation happens when the output of a pump is drastically changed by throttling the discharge valve, increasing the horsepower of the motor without redesigning the size of the discharge pipeline, or by some other discharge restrictions. As the fluid exits the impeller, the velocity is reduced and, as a result, the fluid no longer passes smoothly into the volute and discharge piping. The fluid now tends to impinge on the "cutwater" and induces a vibration at a vibration frequency equal to the vane pass (number of vanes x rpm). It also shows large amplitude readings at vane pass frequency (see Figure 2). 

Figure 2: Spectra showing recirculation

The Analyst as Diplomat

When shaft misalignment is diagnosed, can the analyst/technician offer a corrective solution? In some cases, not at all! In many cases, there can be open warfare between the millwright and the analyst with each claiming the other person is wrong. In reality, both could argue they are right, especially when the millwright shows his "cold alignment" calculations. But if the millwright did not take into consideration allowances for soft-foot, shaft-runout, bracket sag, pump to piping nozzle distortion, and thermal rise into consideration, then the vibration analysis diagnosis is correct.

In addition to being skilled in the arts of proactive maintenance, the analyst/technician must also be well versed in diplomacy, especially when that person does not know how to physically correct the problems diagnosed. Under such circumstances, an analyst should take the time to go out on jobs to at least witness repair work being done. Often, when it is shown that there is an interest in finding out how repairs are carried out, a better relationship will develop.

The analyst as detective
Many times after a problem has been identified, the analyst/technician feels that their contribution to success is over. If the identified problem was related to a failed anti-friction bearing, the analyst would be wise to witness the removal of the bearing and keep the part for inspection before it is thrown in a trash can. When bearings are thrown away, valuable information is also thrown away. This information could reveal whether the bearing suffered damage during installation:
* Was it the correct bearing for the job?
* Did the bearing show signs of lack of lubrication or too much lubrication?
* Was the bearings designed physical characteristic correct?  

These are many of the questions that must be asked when a job fails, and it is the responsibility of the proactive maintenance group to conduct such questioning.

The installation of the replacement bearing should also be witnessed and then checked with vibration analysis after it is back in service. These are some of the basic steps that put precision maintenance ahead of proactive maintenance. For the education of the analyst/technician, the failed bearing should serve to verify their findings of amplitudes and frequencies in the vibration spectrum that characterize antifriction bearing failures.

Hasty V-belt installation can be costly
Taking analysis a step farther brings the analyst/technician into other areas where practical skills are needed to help resolve problems. Simple V-belt installations are perhaps one of the most abused systems in industry. Belts are mutilated when they are being installed because of laziness, ignorance, or a combination of the two. Instead of detensioning the system by adjusting the motors position to slacken the belts, V-belts are pried from the sheaves with a pry-bar, and the new belts are installed using the same method. The inner fibers of the new belts are torn apart and rendered useless from the start. The sidewalls of the sheaves can be easily chipped when belts are forced with pry-bars, causing unbalance of the sheave.

Sheave misalignment is common, and people believe that the flexibility of the V-belts will compensate for this misalignment. This is a big mistake. To determine these faults, the analyst/technician must be aware that three spectra have to be identified in order to do a proper analysis:
1.Driver frequency
2.Belt frequency
3.Driven unit frequency 

Each of these components has their own characteristic harmonics, which point to potential problems within that specific system. When these three fundamental frequencies are identified and broken down, belt problems can be easily resolved, depending on the experience level of the analyst/technician. But if they are not recognized, serious problems will arise and cause considerable damage to the machine. Oftentimes, there can be three problems hidden in one spike in the spectrum; and if the analyst does not take note of the spectral data taken at all three points on a bearing, the resulting diagnosis can be very misleading.

When belts have just been installed and properly tensioned, a straight thin white line should be painted across the width of the belts. This line will serve as an indicator if belt slippage is taking place when the belts are turning and will be highly visible under a correctly tuned strobe light. If a strobe light does not come with the vibration data logger or analyzer, the analyst/technician would be wise to recommend buying one. This tool is indispensable when it comes to troubleshooting rotating equipment, especially fans and drive belts.

Knowledge and experience are the keys to success
To become effective as an analyst, a person who aspires to this demanding job must take the time to master the intricacies of machine design and operation, and couple this with a solid foundation in hands-on maintenance at the shopfloor level. They must be prepared to continually ask questions from experienced people and build upon those experiences until they are competent in this precision maintenance field.

John Robertson is the maintenance reliability specialist for Strategic Work Systems, a consulting firm with offices in Greenville, S.C., and Mill Spring, N.C.  For more information, call , e-mail or visit www.swspitcrew.com.

 MRO Today.  Copyright, 2000

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