Hydrogen Induced Cracking of Electric Welded J55 Casing

Hydrogen Induced Cracking of Electric Welded J55 Casing

A sample of high frequency electric welded API 5CT J55 casing obtained during a mill audit exhibited extensive hydrogen induced cracking (HIC) during SSC testing in NACE Solution A.  Although NACE MR1075/ISO 1516 and API 5CT do not require sour service testing of J55 grade materials, SSC testing was conducted because metallographic examination of the casing revealed significant segregation and irregular inhomogeneous microstructure on one side of the electric weld.  Although microstructure was irregular, it was not martensitic in appearance and SSC was not expected and indeed was not observed after SSC testing.  However, sectioning of SSC test samples revealed extensive HIC.  The casing sample was also subject to tensile testing, impact testing, flattening tests and hardness surveys across the weld region.  All hardness and mechanical test results were acceptable and the casing met the stated requirements of API 5CT.  The casing was produced in a mill that was both API licensed and ISO certified, and had recently passed an API audit of its mill quality plan.  The mill quality plan required all products to be manufactured from continuously cast skelp purchased exclusively from mill-approved vendors.  Mill equipment and procedures for electric welding, seam annealing, inspection and testing were all in accordance with industry best practices.

In this instance the unacceptable HIC resistance of a J55 material which was otherwise deemed suitable for sour service can be attributed to poor quality skelp.  While mill audits and mill quality plans are key to improving product quality, there remains the possibility that poor quality skelp will occasionally find its way into the manufacturing process.  Current inspection and testing requirements of governing standards may not effectively mitigate the risk this poses for materials intended for sour service.  Metallographic examination in conjunction with HIC and/or SSC testing is an effective way to assess the sour service performance of H, J, and K grade electric-welded tubing and casing intended for sour service applications.