Fracture Toughness Testing of a Low Alloy Steel in Geothermal Environments

Abstract

The resistance of a steel to hyarogen assisted cracking is an important design parameter when choosing a steel for use in a geothermal environment. Hydrogen embrittlement arises because of the presence of hydrogen sulphide in the geothermal steam. Other types of environmentally-assisted cracking probably also occur especially at higher temperatures. determination of fracture toughness using a fracture mechanics approach provides a material parameter, the stress intensity for onset of sub-critical cracking, which is independent of specimen size and crack geometry. exposures of test specimens to the geothermal can be used to calculate maximum design stresses and/or allowable flaw sizes for power station components which are to be subjected to the same environment. A program to determine the stress intensity for the onset of subcritical cracking, for a low alloy steel heat treated to different strength levels and exposed to Broadlands steam under simulated turbine conditions is described and discussed.