Utilities' High Energy Piping Systems - Utility Industry's Application of Accoustic Emission (AE) Yields Measurable Improvement in Inspection Program Cost and Overall System Intergrity

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By Charles L. Foster at Pacific Gas & Electric. This article appears in the March/April 1995 issue of Inspectioneering Journal

High energy piping (HEP) systems, main steam lines and hot reheat lines (typically low chrome molydbdenum steels), are susceptible to creep damage. Such damage can lead to leaks, and in extreme cases, catastrophic failure. To ensure safe and reliable operations as plants age, utilities periodically inspect critical components. Conventional inspection methods for HEP systems are radiographic (RT), ultrasonic (UT), field metallography and replication, and magnetic particle (MT) testing.

These methods are labor intensive, require extensive scaffolding for access and removal of insulation. Costs are estimated at 2.6 million per inspection cycle for the 5,000 of hot reheat piping in 5 fossil units. Conservative estimates show at least a 190K, net savings, using AE, at one site, alone.

Use of AE was studies as a global screening technique due to potential benefits. Material defects when stressed by operating conditions emit acoustic energy (elastic strain waves). AE piezoelectric transducers can detect and locate the source of this energy. Centrally located data acquisition equipment collects and analyzes incoming emissions. Follow-up, localized UT or RT inspections, are conducted only at these identified AE source locations.

Less labor intensive than conventional inspection practices, AE requires the installation of waveguides, at 15' intervals, to handle the 950 to 1,000 0 surface temperatures. Sensors are attached to the waveguides. A 4" diameter hole is cut in the insulation at each attachment point where the 1/4" diameter rods are stud welded to the exterior pipe surface.

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