Thermal Aging of Cast Stainless Steel, and Its Impact on Piping Integrity

Abstract

A series of experiments were conducted to characterize the effects of high temperature service (550–650°F or 288–343°C) on the mechanical properties of cast stainless steels. The material studied was Type 316 CF8M stainless steel, which has a duplex structure consisting of ferrite and austenite. Recent studies have shown that thermal aging can result in substantial changes in the Charpy impact energy of this material, and this study was designed to further investigate this finding, and to determine what the impact of this phenomenon might be on the failure mode of piping made of it. To do this one heat of material was furnace aged and tested to determine tensile, Charpy and J-integral R curve properties. To investigate the failure mode of thermally aged piping, entire sections of this heat of four inch (10.2 cm) schedule 80 cast piping were aged and tested to failure after the introduction of large flaws. The results of the test program showed excellent agreement with analytical predictions.