CBM ultrasound testing is performed using an ultrasound listening device in conjunction with data capture software. By recording the sound characteristics of a component under test, the software will make a note of any changes from previous testing or variations against a set threshold. The variations are specific to the conditions of the component under test, and are not compared to a measurement scale or to the sound from similar components (comparative testing). Any significant change will trigger a call to action for further inspection or a warning for pending failures.
When an appropriate ultrasound detection device is coupled with data collection and analysis software such as InCTRL, test results using the CBM method are instantaneous, and can allow the technician to isolate the source or a problem that may not yet be detectable with other technologies. This provides time for corrective action to occur before damage to the equipment and resulting downtime. Another benefit of ultrasound CBM technology is early detection: studies have shown that ultrasound can detect anomalies sooner than other common PdM technologies such as infrared and vibration analysis.
Consider the following summary from a third party evaluation team for the integration of ultrasonic technology in a single organization with over 500 sites:
More than 100 applications were identified in use for various equipment at each site such as boilers, heat exchangers, compressors, motors, pumps, valves, and steam traps.
The total savings for the organization would be approximately$3.7 million annually.
he return on investment for the integration of ultrasound with this cost avoidance would be approximately 15:1.
The annual man-year savings caused by the reduction of time spent diagnosing and troubleshooting would be approximately 45 man-years.
Another adopter of the technology – in this case, a large polyethylene terephthalate plastics recycling facility – is using the InCTRL Condition-Based Monitoring (CBM) program to great success. A full-time employee dedicated to the use of ultrasound has been using ultrasound technology and data collection software to trend 1,300+ test points on a monthly basis for almost five years. The data collected from the software has allowed the maintenance department to get ahead of potential equipment failures and regularly avoid unscheduled downtime.
Step 1: Identification of Critical Components
Critical components are those that can shut down production when they fail or that have a history of premature failure and/or need for frequent replacement. To identify these components, use your CMMS program to generate a history report of past work orders or trace the history of unscheduled shutdowns to pinpoint problem areas. Questions to ask to help determine if components are critical: Would the failure of this component result in reduced plant safety? A halt or decrease in production? Defects in product? A regulatory violation? Adverse environmental effects? If the answer to any of these questions is yes, then the component should be monitored on a regular basis. Generate a list of the most critical components and assign a unit ID number to each component for tracking purposes. It is recommended to initially start out monitoring approximately twenty components. Depending on the size of your organization, this number might be higher or lower. Over time, as the process becomes more natural and you have more experience with the test equipment, the number of components can be increased.
Step 2: Development of an Inspection Schedule
The inspection schedule can either be integrated into a current PM or CBM program, or set up as a separate process. The key is to perform inspections often – once or twice a month for optimum results. If using a current PM or CBM route, select a cycle that is performed during normal operation of the equipment. Equipment must be operating to obtain results with ultrasonic technology. For example, choose a bearing lubrication PM that requires bearings to be rolling when lubricated. Add steps to the PM for ultrasonic CBM inspection. If developing a new CBM schedule, choose a sequence of testing, as well as a frequency and designated time for testing. Test intervals can be automatically set in a program such as InCTRL.
Step 3: Development of an Inspection Schedule
Using the ultrasonic inspection device and a compatible data collection software such as InCTRL, take initial baseline readings of each critical component (InCTRL requires five such samples). When taking the recordings, the sensitivity and gain settings of the ultrasonic device should be set at the lowest possible setting. These settings should be entered into the recorder so that for future inspections, the same settings are used when testing each component and results can then be properly compared. (It is important to note that when testing, settings and operating conditions, such as rpm and load, should be as similar as possible each time, as any variations can affect the reading.)
The individual establishing the threshold samples and performing inspections should be familiar with the equipment and will be able to determine if the recording will provide a good starting point. The manufacturer of the system should also provide guidelines for determining a good baseline. Future recordings can be compared to these baseline recordings for equipment condition analysis.
Step 4: Inspection & Analysis
Following the steps of the inspection schedule and the predetermined settings and attachments, perform regular inspection of critical components. When first starting the
program, take several (four recommended) 20-second long readings/recordings of each component. This will ensure that you get a good recording for accurate trending and analysis. As you become more comfortable performing the inspection, the number of readings per component can be reduced to one or two.
Once recordings are made, replay the files and review both the audio and visual characteristics of the ultrasonic signal to evaluate and analyze the condition of each component. Compare the signal to the baseline and previous recordings. There are very clear differences in the sound and appearances of components in normal versus abnormal condition. For example, a normal bearing typically produces a soft whirring sound. If a bearing is under-lubricated, there will be increased presence of friction. The sound intensity of the bearing will increase, and it will emit an intense scraping sound.
The RMS (root mean squared) value of the signal will also increase and the height of the waveform will visibly increase.
If a bearing is damaged, you may hear intermittent pops or grating depending on the rotation of the bearing and the degree of damage. InCTRL will reflect a heightened crackle count (EPS – Events Per Second) and abnormal spikes in the waveform will be visible.
Step 5: Documentation
All original suspicions should be documented prior to testing. During inspection, any significant changes should be noted. Following inspection, a wave file display of each recording should be printed and filed for future reference and comparison. Acceptable parameters should be established for each critical component. Any changes in condition that warrant special monitoring, further inspection, or repair should be filed in a separate file marked appropriately to reflect urgency. Work orders should also be generated if necessary.
Step 6. Action
Finally, take the necessary action to repair or correct any problems. A CBM program serves no purpose if action is not taken once warning signs of failure become apparent. After the repair is completed, use the ultrasonic device to insure that any new component is installed properly and that the equipment is operating properly.
With a properly implemented predictive maintenance program in place, unnecessary costs may be avoided and the life expectancy of equipment extended. The upfront time investment to implement such a program will be significantly outweighed by the time saved on troubleshooting, shutdowns, and repairs, coupled with increased profit from heightened production and product quality.
In addition to using ultrasonic technology for predictive maintenance, the added benefit is the versatility and diverse application opportunities. High quality ultrasonic inspection devices can also be used for trouble-shooting suspect areas, for verification of repairs and proper component installation, and for air and steam audits.