by John C. Robertson

Precision maintenance does not teach intelligence. It only teaches an intelligent way to make a good job a better one. Precision maintenance is not an option any more. It is a requirement.

Vibration analysis leads the way for other programs
Proactive maintenance relies on the use of electronic instrumentation and computerized programs to effectively pinpoint problems in rotating equipment. Because most problems are mechanical, vibration analysis has evolved as the leading diagnostic tool in proactive maintenance to determine problems and their sources. With the success of vibration analysis, other diagnostic systems have made their debut and each has, in its own way, contributed to enlarging the scope of predicting potential problems in rotating equipment and structures.

It is now commonplace to hear terms such as:

Infrared thermography

Ultrasonic leak detection

Lube oil analysis

Phase angle analysis

Laser shaft alignment

Resonance

All of these programs have brought maintenance activities out of the dark and into a new light. But are these programs really being used effectively? Unfortunately, the answer is often no. In many cases, vibration analysis is only used to monitor machines that require constant maintenance or are classified as critical to production. Consequently, machine life is often extended beyond the critical alert and alarm levels simply because the machine can still run, and production demands it. In such cases, all of the proactive maintenance programs including vibration analysis have degenerated into expensive life support systems.

Communication is critical
Another critical factor that must be addressed is that of the "hands-on" aspect of machinery maintenance. The best diagnostic programs have only the capability to determine what the problem is, but none of them possesses the ability to correct those problems. If there is to be a complete cohesion between those who analyze and those who correct the problem, it becomes imperative that all maintenance personnel receive training about all of the proactive maintenance programs in their plant. Every person who is involved with such a program should be able to communicate with each other in the same language. This is what precision maintenance brings to proactive maintenance programsan understanding of what is going on between departments.

By incorporating the precision maintenance philosophy into the proactive maintenance program, we can extend machinery life spans enormously and increase profits. In order to do this, it must be officially decreed that whenever any machine is scheduled for maintenance, it will always:

Be precision aligned

Be precision balanced

Correct soft foot conditions

Install better shims

Check shaft TIR

And, correct simple resonances on easy-to-get-at components

These simple tasks actually upgrade the jobs of the analysts and maintenance personnel by relieving them of having to continuously monitor suspect machines. They will now have more time to dedicate themselves to developing their skills and communicating with the machine manufacturers about equipment upgrades, training programs and design changes.

Recently, a Canadian oil refinery researched maintenance costs. The costs reflected the time periods when maintenance practices were purely reactive, then preventive, and finally proactive. The chart below shows the costs of performing maintenance within those types of programs. The costs reflected are based on dollars/horsepower/year. Included in the chart are estimated costs that precision maintenance could have brought them.

Vibration analysis compatibility with precision maintenance
Vibration analysis is the separation of vibration signature characteristics that exist in operating rotating and reciprocating machinery. These characteristics are determined by the oscillation of a machine or its parts with respect to a fixed point of reference. This degree of oscillation accurately determines the conditional state of the machinery while it is functional. Vibration analysis is a two-step process that involves acquiring and interpretation of equipment data. Its basic purpose is to determine the mechanical condition of machines and accurately detect any specific mechanical or operational defects. In addition to its ability to sense equipment defects, precision maintenance techniques can use a photo-tachometer or stroboscopic lighting to evaluate structural, piping and shaft misalignment, machinery alignment; determine location of resonance; and correct unbalance in rotating elements, all of which is done using phase angle analysis. Vibration analysis also provides a positive means of determining the correct amount of grease to apply to bearings when lubricating electric motors. These are a few of the finer points that precision maintenance offers as a means of increasing the performance and longevity of machines. This added dimension to a vibration analysis program is not readily found in textbooks but is based on a compilation of proven experience in the field.

Without vibration analysis to warn us of shaft misalignment in machines, industry would experience tremendous losses in production and machinery reliability. Approximately 80 percent of machinery failures can be directly attributed to misalignment symptoms. But how much of that 80 percent can be directly attributed to shaft misalignment? Shaft misalignment indications can be a byproduct of other problems lurking within the machine. Precision maintenance prompts a look in other directions where problems were probably introduced to the machine during its installation, or some earlier maintenance activities. Those problems must be found and corrected.

Precision maintenance uses phase angle analysis as a tool in helping to locate those problems that can contribute to shaft misalignment. If used correctly, phase angle analysis will identify the following problems:

Foundation and baseplate looseness or distortion

Pump nozzle to piping nozzles misalignment

Soft foot

Structural steel looseness

Nodal and anti-nodal points on piping and structures

Resonance

Unbalance of rotating elements

Considering the regularity with which shaft misalignments happen, it is reasonable to assume that laser alignment technology could resolve this crisis. But without the preliminary checks being made to determine that there are no bent shafts, no soft-foot condition, no distortion between piping and pump nozzles, and no improperly grouted bedplate and taking thermal rise into considerationshaft misalignments will continue to plague us.

Laser alignment is credited with being accurate to 1/460th of 0.001 inch. But this is meaningless when we discover that the pre-cut stainless steel shim that is to be inserted under a machine foot is not 0.050 inches as it is etched, but is actually 0.047 inches when measured with an accurate micrometer. This 0.003 inches discrepancy makes a mockery of laser and dial-indicator alignments. The laser and the dial-indicator alignment units are not the culprits. All shims should be measured with an accurate micrometer to verify that they do indeed measure up to the etched size. Those trained in precision maintenance techniques would automatically perform this check before assuming the face value is accurate.

To verify the validity of the shaft alignment against a reported operational misalignment noted by vibration analysis, a "hot alignment" check is often needed. This requires the machine to be stopped and completely isolated per OSHA requirements before the shaft alignment instruments can be reinstalled to verify the readings. From the time the machine is stopped until it is safe to take the measurements, 30 to 45 minutes may have gone by. Meanwhile, the machine cools down by approximately 0.001 inch for every five minutes of downtime. The new set of alignment measurements only verifies the original measurements that were taken when the machine was cold. It is then believed that the alignment is correct and the vibration reading is incorrect.

Unfortunately, this happens regularly. There are some techniques that can verify hot alignment conditions such as the Essinger alignment system (tooling ball method), the Dodd (relative) bar method, and the optical tooling jig transit, but these are usually fixed attachments to a specific machine. All of these systems will accurately measure the running, or hot, alignment condition of machines without having to stop them, thus providing instant verification against a vibration analysis spectrum that questions the alignment.

Ultrasonic leak detectors are now so sensitive that the force that misalignment imposes on a bearing is easily detected by comparing the noise emissions generated on one side of the bearing against the other side. The side of a bearing that emits the greatest sound is where the greatest wear is taking place. By comparing the noise generated on the machines other bearing, the greatest emission should be detected on the opposite side of the bearing from where the first bearings highest reading was recorded.

In too many companies, shaft alignments are controlled by the craftspeople rather than having a company standardized shaft alignment procedure. This procedure should include a check-off list such as:

1) Indicator bar sag

2) Repeatability of fixtures

3) Obtaining dial indicator readings complete with positive and negative signs

4) Recording shaft runout to verify the shaft is not bent

5) Checking for soft foot

6) Consolidating shim packs

7) Stating how much allowance is to be made in machines with thermal growth

Most craftspeople will be familiar with items 1, 2, and 3; but for those who do not understand these points, technical information and advice must be given.

Regardless of the sophistication of the diagnostic tools at our disposal, the means of correcting the problem still depends on the skills of the technician doing the repair work. Good technicians can contribute greatly to a precision maintenance program by drawing on their skills to make observations on failed components that need to be replaced during repair work. Their recommendations must be taken into consideration on how to improve maintenance techniques that will prevent such failures from happening in the future. In order to sharpen these skills, training must be given to teach technicians on how to delve deeper into problem solving.

Analysts/technicians should be technically comfortable in other diagnostic programs because they are complementary to each other; but in order to be competent in these other disciplines, each must become more than just a mechanic or electrician.

Lube oil analysis can provide early warnings
Lube oil analysis is often referred to as tribology, but from the technical dictionary definition of the word, "tribology is the science of the mechanism of friction, lubrication, and wear of interacting surfaces that are in relative motion." For practical reasons, our main concern in troubleshooting problems confines us to the analysis of laboratory findings on oil samples sent in for analysis. Therefore, it is more accurate to say that we study lubrication analysis rather than tribology.

Lube oil analysis is a very effective diagnostic program that can signal a problem long before vibration analysis confirms it. The lube oil is analyzed in a very sophisticated laboratory, and the findings are recorded and sent to the client. Over several analyses, these reports serve as a trend analysis database. After the first report is received, each subsequent report contains the previous reports findings. This is a standard practice with most laboratories, and it greatly helps the analysts to forewarn others of impending problems.

Analysis of oil samples from bearings and gearboxes often prewarn of deterioration that has not yet been diagnosed by vibration analysis. Generally speaking, lube oil analysis and vibration analysis complement each other; and between them, they provide an excellent early warning system of impending failures. As in the vibration analysis program, a good lube oil analysis program must have sampling schedules set for individual machine trains. The sampling schedule should be adhered to for the first 12 months. If there are no appreciable differences in the trends, sampling can be done less frequently. The following is a typical program for a machine over a test period of 12 months:

Lube oil analysis sampling program

Viscosity Every 3 months

Total acid number (TAN) Monthly

Appearance Daily

Water cContent Monthly

Color Weekly

Rust test Every 6 months

Cleanliness Every 1 to 3 months

Rotary bomb oxidation test (RBOT) Every 6 to 12 months

The importance of proper sampling cannot be overstated. In order to make sampling more meaningful, the following practices should be observed:

Never take a sample in a circulating oil system when the oil is not circulating.

Always choose a sample spot that will represent the whole system.

Always use clean sample bottles after the sampling drain valve is well flushed out.

Clearly identify type and source of oil sample.

Seal sample to avoid contamination.

Ship to lab as soon as possible.

Easily conducted tests can be run frequently at the average plant facility. However, a central or base laboratory can run more complex testing with the assistance of the oil supplier or an outside laboratory. If there is a contract with an oil supplier that includes back-up services, use this valuable resource whenever possible. You have paid for it.

The analyst/technician has to be part metallurgist and part chemist to be competent. This does not mean that one must have a degree in those sophisticated subjects, but it does require a working knowledge of how metals are made and why chemical additives are put into lubricants to make them perform better.

Pre-installation bearing care is often overlooked
As an effective part of a precision maintenance program, bearing care must be taken very seriously because all machines have bearings, and some have both sleeve and anti-friction types.

If we consider sleeve bearings and the heavy load conditions that they are subjected to under normal operational conditions, their installation in such machines as turbine generators and huge ocean-going ships require technicians to have skills that go beyond the use of hammer and chisel maintenance. After a newly Babbitted sleeve bearing has been machined and looks nice and shiny, it is still not ready for installation. The bearing must be hand-fitted to the journal that it is to be installed on. It has to be "blued" and scraped to get rid of all of the microscopic peaks that have been left from the machining process. It must show a smooth, peak-free contact area of no less than 85 percent of its load surface.

When a machine is stopped and the lube oil has drained out of the bearings, those microscopic peaks that are left intact on both the journal and the sleeve-bearing surface will pressure-weld themselves because of the weight of the journal and gravitational forces. These welded peaks will shear off when the shaft starts to rotate and the debris will then go into circulation through the lube oil system. These now lead to accelerated wear that the scraping and bedding-in practice would have avoided with precision maintenance practices. Unfortunately, an irate production manager would probably be in orbit by the time such a bearing was installed, but the machine will run longer and better by getting the proper care it needs before installation.

Anti-friction bearings must also be treated with respect, especially during installation. Perhaps the most vulnerable period in the life of such a bearing is when it is removed from its wrappings. It is often left unprotected in a hostile environment where it is handled with bare hands, which expose operational surfaces to skin acids that cause deterioration through acid etching. The most damaging time in the life of an anti-friction bearing is during its actual installation. This is when it is expanded with an oxy-acetylene burner, or it is beaten it into place with a pipe and hammer, or the bearing gets cocked on the shaft and the fitting instructions supplied by the manufacturer are generally ignored. Because of the belief that softer brass or bronze bars are the ideal installation drifts to use for installing bearings, the metal chips that break off these bars ruin many bearings. These chips get embedded in the grease and find their way into the bearing internals where they can cause great damage to the rolling elements and cage. In precision maintenance, common sense dictates that the installation instructions are at least read before the bearing is installed because there is a wealth of information contained in them to help install the bearing correctly.

As a minimum, the analyst/technician should incorporate vibration and lube oil into their trend analysis program, as they are probably the most compatible of all of the proactive analysis programs. Lube oil analysis usually detects a problem before it becomes a vibration problem, but when the two sets of data are tracked, they accurately depict the general condition of the machine.

Infrared thermography as a precision maintenance tool
Thermography uses an electronically produced image representative of thermal patterns on a surface. Those images are recorded on videotape and then downloaded into a computer for storage where the images can be analyzed and reports can be written. Thermography is an excellent means of providing a non-invasive inspection of enclosed high-voltage sources such as motor control centers, transformers, fuse panels, switchgear, and transmission line connections.

In power plants, it is ideally suited for locating boiler casing leaks, chimney stack emissions, diesel engine exhaust gas balancing, locating degrading bearings, defective steam traps and thermal insulation breakdown.

Think of an electrical system as a chain. When the links in the chain are stressed, a breakage will occur at its weakest point. Thermography will locate those weak links in an electrical system before they break. All electrical components produce heat as a function of electrical resistance and sometimes because of inductive heating. These components display temperature differences depending on their state of deterioration. As the components deteriorate, a small temperature rise will be noted initially; but as the rate of deterioration increases, the temperature rise will increase until something eventually burns up or explodes.

If the thermographer is not a qualified electrician, then a qualified electrician should be part of the inspection team. Their experience will be invaluable because of their knowledge of:

The plant layout

The electrical system

The equipment being operated

Where to obtain access to high voltage switchgear rooms and switchyards

Electrical safety

Electrical components and terminology

Where to get assistance

How to correctly open cabinets and boxes

Who to contact in an emergency

This also applies if the thermographer is to work in unfamiliar surroundings such as high-pressure steam systems, HVAC and refrigeration systems etc.

A thermographer should not open any electrical cabinets and panels or go into enclosed steam spaces without being qualified to do so. A thermographer should also be fully trained in lockout and tagout procedures.

If precision maintenance techniques are to be successful, the analyst must be capable of conducting visual inspections and acting upon their observations. Bad practices do not always show up on thermographic scans. Over a period of time, electrical systems deteriorate and problems start to turn up as equipment heats up and cools down causing metal to expand and contract. This in turn causes vibration to loosen screws and bolts, overheating to occur when motors start under load, wire insulation to burn up and circuit breakers to trip. Under these circumstances, thermography will predict failures before they occur. This represents enormous returns on the investment of thermographic equipment when efficiency and profitability increase.

Good procedures support precision maintenance
An effective precision maintenance program requires maintenance procedures to provide appropriate work direction to ensure safety and efficiency. All maintenance departments should develop procedures that are complete, current, and technically accurate. They must be clear, concise, and consistent to minimize the chance of human error. Technically sound maintenance procedures that are combined with craftsmens skills lead to a world-class quality maintenance program. They also provide the following additional benefits:

Decreases the probability of human errors

Clearly defines support requirements for easier job planning and scheduling

Provides procedures as a valuable training aid for inexperienced personnel

Promotes error-free performance through human factors

Provides reliable references for maintenance and system engineers

Pre- and post-maintenance testing
The purpose of pre- and post-maintenance is to provide criteria for evaluating maintenance work during the scheduled shutdown of a machine. A complete set of analytical data is taken on the machine as a database for pre-maintenance activities. After the maintenance work has been completed, the machine is run to permit the same data to be taken again before placing the machine into operational service. A comparison of the pre- and post-data permits the analyst to evaluate the work that was done during the shutdown. If any faults are identified, they can be immediately corrected without having to shut the machine down for an unscheduled repair at a later point in time. Post-maintenance testing also provides guidelines to ensure that equipment performs its intended design functions.

Effective precision maintenance relies on trained people
With all of the sophisticated diagnostic programs that have made their appearance on the plant maintenance scene over the years, none of them can compete with a properly trained person.

Precision maintenance requires that people be properly trained in the finer skills of maintenance. Training programs must be assessed for their instructional value, and their applicability in the work place. Management must be more responsive to the development of this type of maintenance program and understand that when maintenance requires a certain time frame in which to do the job, they will be more understanding of what it takes to do a good job.

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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