By Douglas J. Smith, IEng, Senior Editor
RECENTLY, ROBERT J. DELAUNE, Senior Technical Specialist, Entergy Inc. was asked to identify the location of a leak inside the furnace of a boiler at Entergy’s Little Gypsy power plant. “Because the unit was using an excessive amount of make-up water to keep up with the boiler tube leak it was important to resolve the problem quickly,” says Delaune.
Entergy owns and operates nuclear and fossil power plants in the east, south and southwest U.S. The company also has several fossil-plant support offices that supply engineering, outage management, project design and diagnostic services. Delaune is one of three technical specialists who provide plant support for the fossil operation’s 12-unit division in the Baton Rouge area of Louisiana.
Although the Little Gypsy plant had pressurized the boiler tubes with air and drained the water level below the leak, they were unable to locate the leak. However, using an ultrasonic instrument Delaune was able to scan and locate the leak within a few minutes. The unit was then taken off-line and the leak repaired.
Entergy’s Ultrasonic Testing Program
Ultrasonic instruments detect high-frequency emissions and translate them into the audible range. When a unit is suspected of having a tube or casing leak, Entergy uses the ultrasonic instrument to detect and locate the leak. Using the instrument a technician scans an area and listens through headphones for a distinct rushing sound. With continued adjustments of the instrument’s sensitivity control the technician inspects the leak area until the loudest point is heard.
A rubber-focusing probe, attached to the ultrasonic instrument, allows the technician to pinpoint very small leaks. According to Delaune, when used in conjunction with an infrared camera, the ultrasonic instrument is also able to locate hot spots within the boiler.
When Entergy takes a unit off-line they perform a boiler-casing air test. On the first day of an outage the boiler furnace is pressurized and an infrared camera is used to identify and locate any casing hot spots. After locating the hot spots the technician uses the ultrasonic instrument to locate the leaks. This method helps the technician to identify leaks that may be several feet away from where the hot gases are escaping from the boiler insulation, says Delaune.
Entergy also uses ultrasonics to find leaks in the boiler re-heater tubes. However, since this area is difficult to pressurize, and the tubes are closely spaced, the re-heater tubes are put under a vacuum. Using the ultrasonic instrument the technician is then able to identify the location of any reheater tube leaks by listening for the sound of air being sucked into the tubes.
Ultrasonic leak detection. Photo courtesy of UE Systems.
After documenting the leaks and noting the locations, the technician writes the work requests and transmits them, by email, to the appropriate department for action. Entergy has been using ultrasonic testing since 1985 when they developed their own leak detection diagnostic programs.
According to Delaune, even though the benefits of using ultrasonics are difficult to quantify, the technology is used extensively and plays a major role in Entergy’s comprehensive predictive/preventive maintenance program. “The bottom line is that whether we have boiler-tube or casing leaks we’re wasting energy,” says Delaune. In Delaune’s opinion, ultrasonic technology has helped the utility to reduce controllable losses and reduce the cost of operating and maintaining their plants.