Getting to the source

Portable, ultrasonic instruments make it easier to locate heat exchanger leaks

Doug Waetjen

Ultrasound is defined as high-frequency sound waves that are above the range of human perception. They range from 20 kHz to more than one megahertz. Airborne/structure-borne ultrasound ranges from 20 kHz to 100 kHz.

Airborne ultrasound instruments translate ultrasound signals into an audible range electronically by using heterodyning. As a result, they can then be heard through headphones or seen on a meter or display panel.

Leak detection

Uncovering heat exchanger leaks

ULTRASOUND P the In to a that can is sound rushing distinct for listen sheets. tube access removed usually are heads exchanger Heat leak. signifies inspectors situations, both vacuum. in or pressure under heat whether leaks, detect easily translators Ultrasonic exchangers. suitable inspection.

If multiple heat exchangers of the same type require inspection, a contact method may be used. Contact zones are established along the length of the exchanger shell. An inspector touches each zone with a contact probe and compares the sounds to similar zones on other heat exchangers at the same test points. If a leak is present, the acoustic properties are different. It often produces a loud, popping or crackling sound.

Inspectors also can conduct tests when the heat exchanger is off-line. In such cases, the inspector uses a test unique to ultrasound. It incorporates ultrasonic tone generators, which are placed to produce a uniform ultrasound around the tube bundle. The inspector scans both tube ends and listens for an increase in sound level, which indicates a leak or, in some cases, that a tube is thinning.

Airborne ultrasound instruments are an important part of predictive and preventative maintenance. In addition to heat exchangers, they have proven effective for inspecting bearings, seals, gaskets, pipe systems and compressors.

Ensuring product quality

At a 200-acre manufacturing facility, two-man crews were assigned to check two to five heat exchangers per week to ensure that they were not leaking water into the product stream.

Inspectors pressurized the heat exchangers on the shell side, then brushed a soapy water mix over the tube sheet and ends. If bubbles formed, they knew they had a leak. A complete inspection took days. Even then, it was possible for tiny leaks to go undetected.

After adopting ultrasonics, inspection times were cut by two-thirds. Furthermore, ultrasonics significantly improved the technicians' ability to find the small leaks.

Doug Waetjen is with UE Systems, Inc. He can be reached at 800-223-1325.