Ultrasonics Tool Averts Costly Breakdowns

By: Alan S. Bandes

These days, the value of predictive and preventive maintenance programs is indisputable.  Yet few power plants take the time to shut down an entire system to check for leakage, signs of corona, incipient bearing failure and other often invisible problems.  Increasingly, facilities professionals are using ultrasonics technology in conjunction with other inspection tools.  This method allows for comprehensive surveys of all equipment without interruption of service.   One advocate of such an approach is Jon Thompson, manager in charge of inspections for Bodine Engineering Services & Technology (BEST), in Decatur, Illinois.  The engineering firm provides industrial and commercial businesses with ultrasonic and thermographic surveys and electrical testing services.   Thompson's crew routinely checks everything from compressors, motors, blowers and valves to shafts, bearing rods, steam traps, commutators and electrical systems.  His crew tags every leak and notes the exact nature of each of them.  Finally, Thompson prepares a full report (including infrared color photographs) that flags existing or potential problems.   Customers usually make their own repairs, and an engineer then returns to ensure that all problems have been corrected.  When making a power-on evaluation of a power plant, BEST's primary focus is on electrical distribution systems.   Thompson first uses thermography to scan systems for differences in temperatures.  These detailed infrared color pictures show what the temperature is at a particular point compared to ambient temperatures.  These pictures help Thompson to detect heat loss in buildings or to identify a contact or point of connection that is starting to loosen up.  (Heat is created when the condition of a junction changes.)  At this point, BEST brings in an airborne ultrasonic instrument that is more portable than a thermographic camera.  The tool is used to listen for telltale signs such as corona, high voltage discharge, arcing and leakage.  "In medium and high voltage situations, this tool allows us to listen for tracking on the outside of a cable or tracking over an insulator," Thompson said.  "These problems are not visible to the thermographic camera because we're not looking at a steady state situation where temperatures remain constant.  The ultrasonic instrument hears the sounds -- popping and cracking -- and pinpoints the exact location.  These problems are harmful to the insulator or the jacket of the cable and, if not repaired, could result in either a breakdown or a blow up With preventive maintenance technologies, our customers can make repairs and avert an expensive clean-up after a major burn.  That translates into a savings of thousands of dollars."

OPERATING AN ULTRASONIC INSTRUMENT

Using the ultrasonic scanner, BEST technicians aim the instrument directly at the part of the machine under inspection, making small cross-pattern movements along all exposed sections.  The more sensitivity levels an instrument has, the better it will perform.   If, for example, Thompson suspects that a one-inch pipe is leaking, he waves the gun an inch or two in each direction, moving parallel to the pipe until the leak is discovered.  Then Thompson uses the instrument's close-focus adapter to hone in on the exact location of the leak (the problem may actually be in the fitting.)  For problems out of easy reach, technicians use the ultrasonic instrument with special scanners to test equipment up to 100 feet away.  When testing for leaks in air or blow-off applications by open air tubes, for example, the trick is to focus away from interfering noise and isolate the ultrasonic sounds to locate a leak.  Every leak the technician identifies is tagged with the location and an identification number.  He also records a description of each leak, including its size.  Thompson said it is also a good idea to note the make and serial number of equipment, such as quick couplers, filters, regulators and lubricators that may be causing a chronic leakage problem.  Then the plant maintenance staff can avoid purchasing this part in the future.  It is also important to use the ultrasonic scanner to double check each leak.   The use of confirmation and shielding techniques, such as sealing, always pay off when checking out the entire connection one final time.   Confirmation techniques include moving the ultrasound scanner back and forth over the leak site to confirm the loudest point.  The technician places the rubber focusing probe over the suspected area to seal it off from the environment.  If this is the leak site, the sound will continue; if not, the sound will diminish.  For the shielding technique, the technician uses the rubber focusing probe.   After the repair is made, the technician removes the tag and gives the recording sheet to the power plant so that maintenance people may compare future readings with previously recorded readings to note any differences.

AIR COMPRESSORS

Studies show that compressed air waste and its detrimental effects on energy budgets and profitability are costing manufacturers thousands of dollars each year.    Typically real production demands may only account for 50 percent of the total demand for compressed air.  The remainder is lost.  It is important to identify uncontrolled demand and improper pressure regulation.  It also is important to address poor applications for air, including conventional blow-off. BEST technicians begin each survey by checking the kinds of loads the air compressors are operating on.   They use the ultrasonics tool to establish the sound patterns of properly operating equipment.  Slowly they scan the entire air-line system and identify and pinpoint all air leaks.   Next, they evaluate the system's distribution and storage, and review problem areas with the facility's maintenance people.   "When you have a lot of equipment packed into a small area the ultrasonic instrument can help to identify and isolate 50 to 60 leaks." said Thompson.  "Some of our customers who were contemplating adding an additional compressor learn that there really isn't any need to incur the added expense."

STEAM TRAPS AND BEARINGS

Leaking steam traps can raise a company's operating expenses by as much as a third.  Energy surveys and repairs often save companies hundreds of thousands of dollars.   On almost all surveys, the technicians use airborne ultrasound to quickly reveal the condition of each steam trap.  The ultrasonic test allows the user to hear what is happening within a steam system while it is in operation.  A contact probe used to localize the sound coming from the trap will not pick up other pipe noises since ultrasound intensity drops off rapidly as it moves away from its source.

AIPE FACILITIES

Thompson also uses the Ultraprobe to test for wear in bearings.  "The tool allows us listen for any unusual noise," he said.  " Sometimes it's a little bit of bounce; sometimes we'll hear a flat spot on the ball as it hits the raceway of the bearing.  We can also hear if a bearing is running dry or if there is a small particle of dirt on the ball."  The surveys encourage maintenance crews to schedule periodic greasing of the bearings and they help crews plan convenient times to replace worn ones.

CONCLUSION

Facilities should schedule maintenance surveys of all operating equipment at least once a year, Thompson recommends.  The best plan is to inspect the entire plant department by department always following the same pattern.  Airborne ultrasonic tools and infrared testing are two of the most frequently used methods to conduct surveys and audits.  "Every industrial or commercial business also could profit from a program that educates its maintenance people about testing procedures and sure-fire technologies that eliminate waste and allow the facility to operate more efficiently in the future," Thompson said.

Alan S. Bandes is Vice President of Marketing for UE Systems Inc., Elmsford, New York. He has given workshops throughout the world on the technical and practical aspects of airborne ultrasonic instrumentation.