Specifying Material Toughness to Avoid Brittle Fracture Initiation in Pipe Fittings and Components

Abstract

Recently, there have been a few failures with brittle fractures occurring during hydrostatic or pneumatic proof testing in pipe fittings that rekindled the need for paying attention on how to specify the toughness for pipe fittings and other components such as valves. This paper shows how an analysis procedure called the “Master Curve of Fracture Transition Temperatures” can be used to specify a Charpy shear area percent at some target temperature so that ductile initiation behavior occurs for either a surface or through-wall cracks in fittings, components or pipe material at the minimum design temperature. Due to differences in thickness, loading rate, and constraint conditions, the Charpy test transition temperature will not be at the same temperature as the minimum design temperature. In addition to the background and summary of prior efforts, several examples of full-scale pipe and fitting/valve fracture tests on different materials will be presented to show that the methodology works well. It is also possible from this method to specify the Charpy shear area percent at some temperature to ensure that brittle fracture propagation will not occur. There are some limits on this methodology for some newer steels that have very high Charpy energy values, and those conditions are also summarized.