Choose the right tool for vibration analysis
Vibration collection is the first step toward reliable equipment.
By Mike Bacidore, chief editor
- Predictive technologies, whether hardware or software, vary in price and analytics, but which tool to use typically depends on the type of failure being looked for and then criticality of the equipment.
- The first step toward embracing vibration monitoring and analysis in an appropriate way is to understand how to assign vibration responsibilities within the plant.
- To analyze vibration data requires software, hardware, training, significant asset information infrastructure, and a disciplined schedule.
Vibration analysis is only as good as the data you collect and what you do to correct problems. Just as a healthcare professional might use a stethoscope or an electrocardiograph to measure heart health, maintenance and reliability professionals have wide range of tools at their disposal. These technologies, whether hardware or software, vary in price and analytics, but which tool to use typically depends on the type of failure being looked for and then criticality of the equipment.
“It takes essentially the same amount of money and effort to collect poor data as it does to collect quality data,” explains Sam McNair, P.E., CMRP, senior consultant at Life Cycle Engineering (LCE, www.lce.com), headquartered in Charleston, South Carolina. “Taking RMS vibration levels at one or two frequencies, such as with a handheld vibration pen, is not vibration analysis. To equate it to full-spectrum vibration analysis is to equate a doctor with a stethoscope to one performing an EKG. Both have their proper place in the scheme of things, but they are not the same by any means. Just as an EKG costs more to use, requires more knowledge to analyze, and gives more accurate and definitive results, so does performing full-spectrum vibration analysis.”
Figure 1. Once the site’s machine population is categorized by the consequence of its failure, the overall level of risk is more clearly defined and monitoring and analysis can be assigned from a financial perspective. (Source: Robert Perez)
The quality or degree of the vibration testing is dictated by risk profile or criticality of the machinery. “Reviewing the overall risk profile of a site should always be the starting point for justification of a machinery condition monitoring program,” says Robert X. Perez, author of “Is My Machine OK?” and staff reliability engineer at Enterprise Products in San Antonio, Texas. “The machinery population can be broken up into the broad categories. Low consequence includes small to medium horsepower process machines with low levels of secondary consequences if they fail unexpectedly. This group usually represents the 90% or more of the site’s machinery population. High consequence includes process machines associated with high levels of secondary consequences. If these machines fail unexpectedly, bad things, such as fires, product releases, production outages, and costly secondary mechanical damage, happen. This group can represent about 10% or less of the sites’ population (Figure 1).”
Once the site’s machine population is categorized in this way, the overall level of risk is more clearly defined, explains Perez. If the site is composed only of smaller, low-risk machines, then analysis performed by a mechanic or operator using a vibration data collector or vibration meter is adequate. This level of analysis is limited to trending and simple spectral analysis.
However, if the site comprises a large population of high-consequence machines, then Perez recommends analysis typically performed by a certified vibration analyst, using advanced vibration data collection and analysis hardware and software. This level of analysis involves spectral analysis, phase comparisons, Bode plots, and correlation analysis, he explains.
Mission-critical, complex machines with many variables require a vibration expert to watch them closely, agrees John Bernet, product & application specialist at Fluke (www.fluke.com). “These machines impact plant production,” he stresses. “Companies with this application have no option but to hire a reliability team or outsource to a service consultant. Industries that find they need to do this are petrochemical, pulp and paper, power and others that can’t afford to have any stoppage in production. The maintenance staff doesn’t have the resources, training required, or time needed to trend and analyze the hundreds of rotating machines not supported by the reliability team. The maintenance staff needs easy-to-use vibration testers where extensive setup, trending, analysis, and on-site experts are not needed to get machine-condition answers.”
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 your organization is large enough to have a dedicated reliability team, then vibration monitoring and analysis should be part of that team,” recommends Wayne Vaughn, P.E., CMRP, principal consultant at Vesta Partners (www.vestapartners.com) in Stamford, Connecticut. “It’s valuable to cross-train a person or more on monitoring who work in the maintenance group, both for scheduling flexibility and to develop the career path of craftspeople. If your site doesn’t have a reliability group and is small, then I like the idea of a partnership with outside help for analysis and initial setup, but using maintenance personnel to take the readings and do quick reviews of data.”
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). “They will be in fire-fighting mode, and therefore their priorities will be associated with fixing today's breakdowns,” he says. “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 not be very effective.”
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 they believe 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.”