The Study on Residual Stresses in OCTG and Its Effect on Pipe Sour Cracking (SSC) Performances

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Abstract It is well known that residual stresses in a structure can have a detrimental effect on its flaw cracking process. Through a three-dimensional (3D) finite element analysis (FEA) on a six-roll cold straightening process, it was found that seamless oil country tubular goods (OCTG) pipe has a unique residual stresses pattern due to its manufacturing process. An X-Ray diffraction through wall residual stress measurement shows that even with hot straightening, there is still a significant amount residual stresses existing in the pipe body with a similar pattern found in the cold straightened pipe from FEA. The residual stresses were found to have a significant effect on the pipe sour cracking resistance through an internal pressure burst test of a full-size pipe with a pre-existing flaw in sour environment in an American Petroleum Institute (API) study. A formula was proposed to include the effect of residual stress on determining the sour cracking (sulfide stress cracking) resistance on OCTG tubulars.

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