Hydrostatic Pressure Testing for Exacerbation of Stress Corrosion Cracks (SCC) in Nurse Tanks (Phase IV)
To collect original data on the safety impact of hydrostatic testing of nurse tanks.
There are three testing methods commonly used to evaluate the safety of nurse tanks, and each has significant limitations. They are: visual inspection, thickness testing, and hydrostatic testing. Industry experts have openly pondered whether hydrostatic pressure testing exacerbates existing cracks, making them more likely to fail in the future. There is no data available on the long-term safety impact. Previous research by Iowa State University established that single angle-beam ultrasonic testing is a non-destructive method for detecting the existence of cracks, but it cannot tell the depth of penetration of the crack within the tank steel. The use of phased-array angle- beam ultrasonic testing may present an opportunity to: 1) map the existence and penetration of cracks in a limited number of test tanks, 2) subject those tanks to hydrostatic tests, and 3) collect acoustic data to determine whether the hydrostatic testing caused the existing cracks to expand.
The purpose of this research effort is to establish the detailed crack map (location and penetration) for a small number of nurse tanks; apply hydrostatic testing to those tanks with the known crack map; use acoustic listening devices to triangulate any sounds from any part of the tank that result from the hydrostatically applied stresses; and then verify with the phased-array ultrasonic angle-beam inspection whether any known cracks were exacerbated by application of the hydrostatic pressurization of the test nurse tank.