Reheat Cracking of Low Alloy Steel During Fabrication and in Service in Oil and Gas Facilities

Abstract

Abstract Reheat Cracking is usually associated with the heat affected zone of restrained welded joints during either post weld heat treatment or elevated temperature service. Cracking is associated with the formation of fine intragranular precipitates. This precipitation strengthens the grain interiors and transfers the strain necessary for the relief of residual welding and system stresses to the grain boundaries. The overall effect is a reduction in creep ductility leading to intergranular failure in creep resistant steels. This mode of cracking poses a considerable practical problem particularly because the microstructural and compositional factors affecting its occurrence have not been clearly defined. In this paper a literature review, case histories descriptions and research in progress are summarized. The case histories include one overhead fluid catalytic cracking reactor overhead line during fabrication post weld heat treatment) and three high temperature high pressure steam piping after long and short term in service. Research in progress includes the developing a testing procedure and the quantification of local strain level leading to stress relief cracking (SRC) during post weld heat treatment (PWHT) of welds in creep resistant steels. The testing approach involved implementation of a digital image correlation (DIC) technique with Gleeble-based SRC test.