Of the technologies available for condition monitoring of rotating equipment, the quickest return on investment is from vibration analysis. For the novice, vibration data seems complex and is generally difficult to assess compared to other techniques. Once trained, however, the novice can recognize the patterns and diagnose a machine problem.
This article highlights a new type of vibration analysis training and implementation. It is directed toward managers and individuals who make the decisions to shut down equipment with vibration problems or keep it in operation until an outage. It is based on the most important techniques used in vibration analysis and is not intended for Level 3 or 4 vibration specialists and consultants.
The goal of this article is to introduce a new approach to implementation of vibration analysis programs. This approach will highlight the active role of decision makers, equipment owners and managers in the analysis of equipment vibration without being experts in vibration analysis.
Present Condition Monitoring (Vibration Analysis) Systems
At present, three major systems are popular:
- Internal vibration analysis team, usually adopted by large companies
- External consultant
- On-line condition monitoring systems
Internal Vibration Analysis Team
This team often performs the studies on equipment reliability and makes suggestions for changes. The advantages of the internal vibration analysis team are:
- Close attention given to rotating equipment issues
- Fast response because they are company employees
- Reports will be well documented and organized in easily accessible files
- High specialization of employees is possible
- All suitable equipment will be covered by the condition monitoring program
- Data collection intervals will be reasonably short
The disadvantages of the internal vibration analysis team are:
- Relatively high cost of implementation
- Condition monitoring equipment installation, update and calibration
- Computers and office equipment
- Training
- Plant equipment modification to allow easy data collection
- Office space allocation for vibration analysis team
- Problems could be exaggerated to emphasize the team's importance. For instance, an analyst might recommend repair for equipment of unclear condition, when no repair is required. Maintenance-induced defects could increase.
The most efficient vibration analysis programs employ highly qualified vibration analysis specialists. An average or below average vibration analyst might be detrimental for the overall maintenance cost and general condition of plant equipment, due to his inability to detect critical problems. This negative effect comes not only from the average analysts, but also from the organizational structure in which the vibration analyst works. The analyst produces reports that provide the production/operation/maintenance management the data required to make decisions regarding equipment: whether to operate at full capacity, restrict the operational parameters, perform preventive tasks or stop the equipment for overhaul.
The equipment covered by vibration analysis reports falls into three categories: suitable for unrestricted operation, unclear condition and not operational. Management may be confused by an "unclear condition" description and require additional meetings, emails, letters and clarifications.
External Consultant
The second solution is to outsource the vibration analysis to an external consultant. The advantages include low implementation cost and access to the knowledge of a highly qualified specialist.
The disadvantages of an external consultant are:
- The program cost is high, due to consultant fees.
- Data collection intervals are generally long.
- The response for specific issues may be slow.
On-line Condition Monitoring Systems
Some companies implement on-line condition monitoring systems for suitable equipment. Some of the new on-line systems, in addition to automatic shutdowns and alarms, also generate vibration data that requires interpretation in one of the two ways described above.
The advantages of online monitoring include:
- Automated scheduled data collection and no need for walk-around
- Minimized need to enter hot and dangerous areas
- Ability to capture data on running equipments only
- Short recording intervals
- Can be part of automated remote monitoring or protection system
The disadvantages of online monitoring are:
- Expensive installation of sensors, cables, instruments and communication infrastructure
- Data can be overwhelming if not managed properly
- Alarm settings maybe less sensitive to changing conditions of the equipment
The New Approach
The reason for requesting consultant services or employing a vibration analyst may be management's lack of vibration analysis knowledge, or the misconception that management does not have time to perform the vibration analysis.
This is valid for large companies, but there are many small to average-size companies where the manager/decision maker has time to perform the vibration analysis. Even a person trained in vibration analysis will spend more time reading the vibration analysis reports, clarifying the equipment condition and determining the corrective action than diagnosing the vibration spectra.
The manager with a good technical background, reasonable scope of work and comfort with computers should be ready to accept the challenge of specialized vibration analysis training. Managers and decision makers can perform vibration analysis, decide whether to keep the equipment operational or schedule the equipment for maintenance.
Vibration Analyst Techniques for Managers
A study of the techniques experienced vibration analysts use shows some methods that are well accepted and used regularly. One essential analysis technique is spectral analysis. Without spectral analysis, decisions based on overall vibration levels, band levels and bearing parameters are not accurate.
Table 1 summarizes the most common vibration analysis techniques and their importance for managers planning to become vibration analysts.
Table 1
| Vibration Analysis Technique | Importance |
|---|---|
| Spectral analysis | Compulsory |
| Overall limits | Important |
| Phase analysis | Important |
| Bump test (resonance) | Important |
| Ramp up (resonance) | Optional |
| Overall trends | Optional |
| Waveform analysis | Optional |
| Real time/live mode analysis | Optional |
| Coast down (resonance) | Optional |
| Bode plots (resonance) | Optional |
| Polar plots (resonance) | Optional |
| Bearing parameter + trends | Optional |
| Orbit analysis | Unnecessary |
| Band trends | Unnecessary |
| Cepstrum analysis | Unnecessary |
| Operation deflection shape | Unnecessary |
| Band limits | Unnecessary |
Selecting the "Compulsory" and "Important" techniques only yields dedicated, achievable training for managers (see Table 2).
Table 2
| Selected Vibration Analysis Techniques |
|---|
| Spectrum analysis |
| Overall limits |
| Phase analysis |
| Bump test (resonance) |
The largest percentage of vibration issues are related to misalignment and unbalance and are easily detected using the selected techniques in Table 2. Looseness, hydraulic deficiencies, bearing failures, lubrication, gearbox-related issues and many forms of resonance are also easily monitored using these same techniques.
Organizational Structure with Vibration Analyst Managers
After learning vibration analyst techniques, the manager/decision maker can analyzes the data that the maintenance technician collects. The manager will make his decision based on his own vibration analysis.
Case Study
One of the world's largest district cooling companies tested this new approach to vibration analysis by managers. The database contained approximately 800 pieces of equipment.
Six maintenance technicians collected data. The availability of the rotating equipment maintained was approximately 97 percent. When the company expanded, the manager performing the maintenance tasks and the vibration analysis became overloaded.
This availability rate was high for the following reasons:
- The equipment was well known by the manager/analyst and any additional tests were promptly organized, until the condition of the equipment was positively clarified.
- The equipment was relatively simple (pumps, fans, centrifugal compressors, gearboxes, etc).
- The manager performing the vibration analysis was an experienced analyst.
- The vibration analysis tools and the regular technicians' training in data collection made possible the use of vibration analysis as an efficient quality control tool for breakdown maintenance.
- The maintenance technicians and plant-room operators' awareness in vibration analysis issues was high.
- The vibration data increased the efficient planning of breakdown maintenance and optimized the preventive maintenance program.
- The vibration analysis reports were simple, and corrective action was quickly taken.
The presence of vibration analysis tools and the regular technicians' training on data collection made it possible to control the quality of the execution of breakdowns. In addition, the maintenance technicians' and plant-room operators' awareness in vibration analysis issues was high. The vibration data had been used in efficient planning of breakdowns and in optimizing preventive maintenance.
Recommendations
Combining the vibration analysis and maintenance responsibilities is recommended for companies with the following conditions:
- The vibration analysis equipment acquisition is not a financial burden and is justified by the savings on the equipment breakdowns.
- The rotating equipment suitable for vibration analysis is limited to 200 to 500 pieces, depending on the equipment complexity and manager's skills. Larger companies can split the scope between two or more managers, but should also consider a specialized vibration analysis team.
- The technical level of the vibration analyst performing the analysis in addition to normal maintenance tasks is appropriate.
- Management is open to new solutions and ready to support the person who is assuming the combined responsibilities in implementing the new system. This person can have either maintenance or condition monitoring background, or, ideally, both.
- The criticality of the equipment is reasonable.
Advantages of implementing vibration analysis as part of maintenance decision-maker responsibilities include:
- Increases the equipment reliability and availability through realistic assessment of condition.
- The maintenance cost will be kept low, without affecting the equipment condition.
- In general, no new employees are required. Since financial justification toward higher management is much easier, the implementation of the program is more probable.
- The manager's time is better used by avoiding time-consuming clarifications between departments.
- Maintenance-induced defects will also decrease.
- Condition monitoring is required for any modern maintenance strategy.
- Vibration analysis continues to gain popularity, with good results for plants with continuous processes.
- Vibration analysis consultants offer support in system implementation and future assistance.
Summary
A maintenance manager can fill the role of vibration analyst since he has the authority to quickly determine if a machine needs to be shut down for repair. This method works for small to medium-size plants. If the program expands beyond the scope of the manager, the duties can be split among area managers.
Pumps and Systems, June 2009