Inspectioneering Journal

Utilities' High Energy Piping Systems - Utility Industry's Application of Acoustic Emission Yields Measurable Improvement in Inspection Program Cost and Overall System Integrity

By Charles L. Foster, Staff Engineer at Pacific Gas & Electric. This article appears in the March/April 1995 issue of Inspectioneering Journal.
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High energy piping (HEP) systems, main steam lines, and hot reheat lines (typically low chrome molybdenum 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 $190,000 in net savings, using acoustic emission (AE), at one site, alone.

The use of AE was studied 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.

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