Abstract
The combined effects of time-dependent environmental and stress conditions on IGSCC of sensitized Type 304 stainless steel were studied in high temperature and high purity water. Tests were conducted on small tubular type specimens under cyclic conditions of water temperature, dissolved oxygen concentration and stress with a triangular wave form simulating the start-up and shut-down operations of boiling water reactors.
The test results showed that IGSCC was significantly accelerated by cyclic rise and drop in the temperature range 145 to 290°C, and/or cyclic changes of dissolved oxygen concentration between 0.2 and 8ppm. Whereas, the susceptibility to IGSCC was lower under cyclic stress between 16 and 28kg/mm2 than at a constant stress. IGSCC caused by cyclic changes of temperature is attributed to the rupture of oxide film due to dynamic strain, and/or differences in thermal expansion coefficients of oxide film and metal. It was concluded that control of heating rates and dissolved oxygen concentration during the start-up operation is very important to prevent IGSCC of stainless steel piping.
