Leak Detective Sleuths Out Trouble (March 26, 2010)
How an ultrasound inspection saved hundreds of thousands of dollars by finding vacuum leaks hidden underneath ...
How an ultrasound inspection saved hundreds of thousands of dollars by finding vacuum leaks hidden underneath thick pipe insulation.
A major industrial facility had an urgent need to locate a vacuum leak in a pipe that was insulated in 1.5-in.-thick rock wool covered by an aluminum outer skin. The cost of downtime at the facility was estimated at $35,000 per hour, and the time the maintenance department had allocated for locating the leak or leaks was one full shift (eight hours). It was going to be expensive!
A service inspector from Enercheck Systems was called in and he asked to have the system pressurized with compressed air. The test pressure was set at 25 psi to 30 psi. The inspector used an ultrasound detection instrument that sensed ultrasound emissions produced by a leak. The instrument then translated these sounds down from the high frequency range.
Through headphones supplied with the instrument, the inspector was able to hear the low frequency or audible range where the leak sounds were coming from, and also could see intensity increments of the sound via a display panel on the back of the instrument.
While scanning the first section of the piping with the ultrasonic instrument, the inspector noted that a 250-lb steam line close by was creating excessively loud ultrasounds. Since it was anticipated that the leak sound would have to penetrate through the insulation and would be substantially lower in volume than the steam-generated noise, the inspector requested that the steam line be temporarily turned off.
After the steam line was shut off, the inspector used a module to sense airborne ultrasounds, referred to as a scanning module, and located three leaks. The leaks were repaired within a few hours by welding them closed. The inspector then noted a drop of pressure in the system pressure gauge and determined that there were still more leaks to find. He resumed scanning the pipe system with his ultrasound instrument, but was unable to identify any more leaks.
Time was short
Speaking of pressure, the facility was depending on the inspector to find all the leaks before the evening shift began. He asked for permission to make test points in the insulation by perforating the aluminum skin with a sharp screwdriver. Out of necessity, permission was granted. The inspector made a series of strategic perforations on each side of the 8-in. piping system.
He switched to a module used to inspect structure-borne ultrasound, called a stethoscope or contact module. This is a module with a solid metal rod on the end that acts as a wave guide to transfer structure-borne ultrasounds produced by a leak to the instrument’s sensor. He carefully inserted the wave-guide into the holes he fashioned and listened for any increases in the sound.
It was not until the inspector came to an elbow in the system that he heard what he believed was the source of the problem. The insulation was removed and to everyone’s relief, a leak at the elbow was confirmed.
Then the problem became evident. Although the majority of the system was constructed in 316 stainless steel, the elbow was not. To temporarily fix the leak, soft putty that hardens in less than 10 minutes was fashioned over the leak. It was hypothesized that because the system was pulling vacuum, the putty would be sucked into the leak site just enough to stop the leak.
While the system was changed from positive to negative pressure, the inspector made a final scan. The supposition was correct. All of the leaks had been identified and repaired, and the facility could resume its process.
The inspector has checked back several times and confirmed that the facility was able to run its process for the two weeks necessary to have the part it had in production completely fabricated. For Enercheck Systems, it was just another success story of using ultrasound detection equipment to spot leaks. For this major industrial facility, the leak detection helped keep order fulfilment on track, potentially saving hundreds of thousands of dollars in downtime.
Bruce Gorelick is vice-president, Enercheck Systems, Charlotte, NC, and Alan Bandes is vice-president marketing, UE Systems Inc., Elmsford NY. For more information, visit enerchecksystems.comand uesystems.com.