10 Critical Elements for Successful PdM | 1Special Report

SUPERCHARGEYoUR vibRAtionPRoGRAm Are You Extracting the Full Value

From Your Vibration Analysis Program?

Supercharge Your Vibration Program | 2

“Operators have a much better connection with the machine and

the process, and it’s in their interests to detect faults before they become

potentially dangerous.”

Vibration programs are filled with potential. It’s often initiated with very good intentions. Some-times those intentions are triggered by a critical failure that caused injury or that affected the

plant’s production. Unfortunately, many programs fail, but only because of a misunderstanding of proper preparation and implementation or a lack of dedication of proper resources. Many programs follow a common path to demise, normally occurring in the first year or two. The key is to super-charge your program before it sputters into the abyss.

Unfortunately, the most critical and complicated machines are typically chosen as the first machines to add to the database. Without proper understanding of vibration analysis, default data collection settings are used and basic tests are made, which often are inadequate, especially for the complex machines selected for the program startup. Some alarm limits are set, but improper under-standing results in false alarms that are soon ignored. Faults are detected in their late stages, causing repair work to remain urgent and reactive. The first steps down the road to failure have been taken.

The path continues as analysts can’t explain their reports, so stakeholders question diagnoses. Emphasis is made on bearing faults, and other problems are ignored. Catastrophic failures still occur, and skepticism grows. Finally, resources are pulled from the program; either consultants are brought in or it’s scrapped all together. We have arrived at our destination — disaster.

Vibration analysis is a proven condition monitoring technology. Unproductive or marginally productive programs are usually a result of improper planning and implementation or placing trust in under-qualified analysts. Analyzing machine fault conditions from the vibration spectra is just a small part of the whole job. Training is incredibly important. Management must:

• understand and hold close the greater objectives of condition monitoring and predictive main-tenance

• be able to recognize and understand the relationship of qualified analysts to the program’s health• understand why you “detect to prevent”• understand the importance of performing root-cause analysis and correcting inherent faults.

Whose vibration is it anyway?The first step toward embracing vibration monitoring and analysis in an appropriate way is to understand how to assign vibration responsibilities within the plant. If an organization is starting a vibration analysis program, then chances are high that the maintenance department will be in reactive mode, explains Jason Tranter, managing director and founder of Mobius Institute (www.mobiusinstitute.com).

“The maintenance department will be in fire-fighting mode, and therefore their priorities will be associated with fixing today’s breakdowns,” explains Tranter. “If the vibration analysts don’t have 100% focus on the vibration monitoring program, then they will be constantly distracted; their data collection routes will be delayed more and more, and thus the program will be ineffective.”

Supercharge Your Vibration Program | 3

If the organization has a reliability group, then hopefully that means that the organization is thinking about improving the future, continues Tranter. “Condition-based maintenance is all about fixing tomorrow’s problems so they don’t become today’s problems,” he explains. “The maintenance department will hopefully be better able to deal with a condition monitoring program if it believes in reliability improvement. But, if the maintenance department is in fire-fighting mode, it isn’t a good place for a condition monitoring team, unless they have the independence to do the job properly and the support to have their recommendations acted upon.”

In an ideal world, the vibration analysts would have enough time to test all machines with suffi-cient frequency to detect faults at the earliest stage and monitor the progression of the fault. Spend-ing a lot of time with the machines has numerous benefits, says Tranter. “But, if the budget doesn’t support this effort, then a very good solution is to involve operators in the program,” he suggests. “Operators have a much better connection with the machine and the process, and it’s in their inter-ests to detect faults before they become potentially dangerous. If the operators detect a change in vibration by using a simple meter or ultrasound, then they can call for the vibration analyst to come and perform a complete analysis.”

It is interesting to categorize vibration analysts in three ways, says Tranter, who explains the ana-lyst types in detail.

Type One analysts recognize fault conditions because they’ve seen them many times before on the same type of equipment, and they rely on that experience.

Type Two analysts rely on cookie-cutter patterns that are seen on wall charts. This group also includes OMG analysts — “OMG, the vibration is high. We’d better stop the machine and find out what’s wrong!”

Type Three analysts understand the machine and can determine the condition of the machine by using a combination of knowledge and experience.

Type One AnalystsMany analysts have a tremendous amount of experience and can diagnose faults quickly. They either rely on experience alone, or they understand the machine and tools and know why the vibration changes. The first group comprises Type One analysts, while the second group is Type Three.

“Type One analysts work on the same type of machines, perhaps even the same machine, for many years,” says Tranter. “Some 10-year analysts have one year of experience repeated 10 times. They can remember how the vibration changes as the fault develops, and they’re valuable to have on staff, but they’re hard to find.”

It takes a lot of trial and error to become a Type One analyst. It takes the support of a patient manager/supervisor to accept the trial and error — not that any analyst is perfect, but when you rely on experience alone, you have to experience success and failure to learn.

“If the vibration analysts don’t have 100% focus on the vibration monitoring program, then they will be constantly distracted.”

Supercharge Your Vibration Program | 4

Type One analysts typically dismiss the need for training and certification. You can’t teach 10 years of application-specific knowledge, and you can’t test people on the specifics. Training and certification have to be broad-based.

Type Two AnalystsMost managers don’t believe in the principles of predictive maintenance. Unless the bearing is about to fail, they won’t take any corrective action. Fault conditions such as unbalance, misalignment, and other conditions that will ultimately damage the machine are ignored unless the vibration levels are very high.

As a result, vibration analysts can take a very simple approach. “Rather than focusing on bearing fault detection at the earliest stage and rather than making the effort to determine whether the ma-chine has a fault condition that will result in premature failure of the bearing or other component, most analysts try to stay one step ahead of the guy who listens to the bearing with a screwdriver,” says Tranter.

If you identify vibration changes, whether it’s the result of the bearing failure or not, and the machine can be stopped before it fails catastrophically, then that vibration program is avoiding downtime and resulting secondary damage, including potential injury or environmental harm. But such a program may not garner the greatest benefits of the vibration monitoring technology.

“These vibration analysts may evolve into Type One vibration analysts, given enough time,” says Tranter. “They begin to recognize some of the tell-tale signs of a developing problem. If they’d taken the time to find out what was actually wrong with the machine during earlier failures, then that expe-rience may be put to good use.”

Most Type Two vibration analysts won’t look at the bearing after it’s removed from the machine to determine how severe the damage was, says Tranter. “They won’t ask the craftspeople what was actually wrong with the motor when it was removed from service,” he explains. “Type Two vibration analysts will just continue monitoring the vibration and looking for the next problem.”

In defense of Type Two vibration analysts, they’re often not given the opportunity to do a better job. They need management support, so they can see that their contributions are valued.

“They need to work in an environment where condition-based maintenance and reliability is a priority, and they should be given adequate training — more than a three-day course on how to oper-ate the equipment and run the software,” explains Tranter.

The vibration analyst needs to fully understand why the settings of the vibration analyzer are im-portant, what the failure modes of the machine are, and how the vibration changes with the various failure modes.

Type Three AnalystsThese are the best analysts. They have experience and training, and they’ll seek out the tough jobs,

“For large machines, the transmission of high-frequency vibration is greatly

attenuated through the machine’s structure and might be difficult

to detect.”

Supercharge Your Vibration Program | 5

utilize all the tools, and leave no stone unturned when trying to diagnose a fault. Type Three analysts will also give the clearest diagnosis and recommendation.

Being a Type Three analyst requires the right type of training. Focusing on detecting bearing faults alone, or focusing on cookie-cutter patterns isn’t enough. Type Three analysts:

• understand the machine failure modes • understand how the vibration of the machine will change as the fault develops• understand how and where to measure the vibration to get the best data• understand the analyzer and the analysis options well enough to be sure they’re capturing and

seeing all the details revealed by the machine• understand why the vibration changes the way it does so they can reverse-engineer what is going

on inside the machine.“The wall charts can remind an analyst of what the patterns might mean, but relying on them is

the equivalent of guessing what is wrong with the machine,” explains Tranter.

Machine Vibration and Failure ModesMachines vibrate in three dimensions, explains Tranter. The nature of the fault and the nature of the machine dictate how much. Whether the machine is vibrating in the vertical, horizontal, or axial direction, the nature of the fault, or the failure mode, dictates whether a spectrum can pro-vide the information that will allow an analyst to diagnose it.

“When an impact, rub, cavitation, or turbulence occurs, the time waveform will reveal key infor-mation,” explains Tranter. “And with a large number of fault conditions where there are directional driving forces, phase measurements provide key information. With a different group of fault condi-tions, very high frequency data will reveal the earliest and most comprehensive details of the fault condition.”

At each point on the machine, the vibration depends which type of bearing — for example, sleeve bearing, deep groove bearing, thrust bearing, floating bearing — is being tested; how the vibration is transmitted from the rotating elements to the measurement location; how the sensor is mounted; and the type of sensor. The data is only as good as what’s collected.

“Type Three analysts ensure the data, with the exception of phase data and other special test data, is collected properly,” says Tranter. “They also understand the value of just standing next to the machine and using their senses to understand the machine condition.

Sometimes, a machine’s vibration changes from one rotation to the next. The story it tells can involve noise, short-duration events such as impacts, or high-frequency or low-frequency sounds. All relevant data must be collected so the analysis is both comprehensive and repeatable.”

Detect to PreventFrom vibration readings taken on rotating machinery, analysts can detect all manner of fault

“Condition-based maintenance is all about fixing tomorrow’s problems so they don’t become today’s problems.”

Supercharge Your Vibration Program | 6

conditions. They can tell if the machine is misaligned; they can tell if a pump is cavitating; and they can even tell if there is damage on the inner race of a rolling element bearing, says Tranter. “A successful vibration monitoring program can decrease maintenance costs through reduced down-time, minimized secondary damage, reduced labor costs, and improved safety,” he says. “If faults are detected in the earliest stages, maintenance can be planned when it’s most convenient.”

However, many vibration analysis programs don’t achieve their full potential because they only detect faults that in the machine. They don’t improve reliability. A true measure of reliability im-provement should be a reduction in the faults that develop in the machines. “Vibration analysts shouldn’t detect misalignment that results from poor alignment practices,” says Tranter. “Vibration analysts shouldn’t detect cavitation. And vibration analysts shouldn’t detect faults in rolling element bearings, unless the bearing has been installed for a very long time.”

Some fault conditions will develop over time due to normal wear, but many fault conditions develop because the machine was transported, installed, operated, lubricated, or aligned incor-rectly, or because it wasn’t ideally suited to the application. Rotating machinery and the individual components are often selected based on price, not reliability. Total cost of ownership isn’t taken into consideration.

To achieve the greatest reduction in maintenance and operating costs, the vibration analyst’s job shouldn’t be limited to the detection of fault conditions. The analyst should be involved with reli-ability improvement.

Initial Design and PurchaseWhen a specification is put together for a new piece of equipment, achieving high reliability should be a key goal. “The vibration analyst should be consulted when rotating equipment is to be purchased,” says Tranter. “In an ideal world, machinery with easy-to-access monitoring points would be selected.”

Don’t assume components, lubricants, and the machines themselves are in perfect condition when they’re purchased. This isn’t always the case. “Bearings may not be transported or stored cor-rectly and may suffer from false brinelling,” explains Tranter. “Lubricants may not meet cleanliness standards. Rotating machinery may suffer from resonance or other conditions when operated under normally. Rarely is rotating machinery designed with energy efficiency and reliability in mind.”

Acceptance testing provides a way to test that machines and components are in good condi-tion before they’re installed. It puts pressure on the supplier to deliver quality. Acceptance testing guidelines can include specifications on a number of parameters, but, from the vibration analyst’s perspective, the key standard is to set vibration limits that may not be exceeded. “Tests may be performed at the OEM’s workshop or after being installed on-site,” says Tranter. “The conditions for the test, including RPM, load, and mounting, must be clearly specified.”

Acceptance testing should be performed when repair and overhaul work is performed, too. This

3 Steps to Vibration Success | 7

can include motor rewinds, rotor balancing, and pump rebuilds. Numerous ISO standards provide guidance for acceptable vibration limits when equipment is new or overhauled, and a number of specifications exist in the public domain, as well.

Many vibration analysts are involved with field balancing and shaft alignment. Balancing reduces rotating forces that can damage bearings and the machine structure. And shaft alignment reduces the stress on bearings, couplings, and the shaft itself. Even if the vibration analyst doesn’t perform the shaft alignment or balancing function, vibration readings should be taken before and after the work to ensure it’s done right.

Set targets when performing shaft alignment and field balancing, recommends Tranter. “Stan-dards from the ISO, API, and the U.S. Navy are readily accessible and provide an indication of bal-ance quality,” he says. “While the G 6.3 standard is recommended in ISO 1940, G 1.0 should be the target, if precision maintenance is your goal. The equivalent API standard is G 0.7.”

Rotating-machinery OEMs will often provide shaft alignment tolerances, and the laser alignment manufacturers will provide guidelines. “One standard that shouldn’t be used is the specification provided with certain flexible couplings,” warns Tranter. “These very loose specifications provide an indication of what the coupling may survive but they don’t provide an indication of what’s best for the long-term operation of the machine.”

Resonance occurs when a machine generates vibration at a frequency close to a natural frequency of the rotor or structure. Resonance increases the vibration amplitude, and a high vibration ampli-tude reduces the life of the bearings and the machine structure.

The vibration analyst can identify the source of the vibration that’s exciting the natural frequency and seek to reduce that vibration amplitude. For example, if there’s unbalance that’s exciting the natural frequency, then one solution is to balance the machine.

The vibration analyst also can help by performing tests that identify the natural frequencies and then proposing modifications to the structure so the natural frequencies no longer correspond to the frequencies being generated by the machine. The most common situation occurs when the running speed of the machine corresponds with the natural frequency; however, other sources of vibration such as the pump vane rate or blade passing frequencies can excite natural frequencies. “It may be necessary to increase the stiffness of the structure to increase the natural frequency, so that it’s no longer excited by the vibration generated by the machine,” recommends Tranter.

Root-Cause AnalysisUnbalance, misalignment, incorrect belt tension, poor lubrication practices, incorrect machine operation, and resonance are common root causes of failures in rotating machinery, but many others exist. “When the vibration analyst detects a fault in the machine, the root cause should be determined so measures can be taken to eliminate it,” says Tranter. “The ability to detect a bear-ing defect is clever, but not if the same bearing exhibits the same fault condition months later.”

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Mobius Institute provides unique and easily understandable vibration analysis training and certification to Predictive Maintenance (PdM) technicians and Reliability Engineers, allowing companies to operate at higher levels of availability and profitability.

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