A threaded coupling in the production tubing string in an oil well at a tension leg platform in the Gulf of Mexico failed in June 1999. The coupling was a 110 grade, 15Cr martensitic stainless steel. The fracture was longitudinal, through-wall, the entire length of the coupling, and intergranular. Neither harm to personnel nor release of hydrocarbons to the environment occurred because of this failure. This paper presents and discusses the results of a laboratory failure analysis from which it was determined that the fracture was caused by the heat treatment. The fracture was not caused by the production environment or by any other well-bore fluids. The fracture mode was duplicated in unused product in the laboratory. The QA/QC in place for the order did not detect this problem.
In June 1999, a premium threaded coupling of a 5-½ inch (140 mm), 22.54 lbs/ft production tubing failed during service in an oil well at a tension leg platform in the Gulf of Mexico. The well environment was sweet. The tubing and the coupling were made from the same material, a quenched and tempered, 110 grade, 15Cr martensitic stainless steel with a nominal composition of 0.1C-14.5Cr- 1.7Ni-0.4Mo (a subset of UNS $42500). It was the first such use for this grade of this material. The well fluids were safely contained within the riser and no hydrocarbons were released to the environment. The well was shut in and the tubing string was recovered for evaluation. The well had been in service for a short period of time when the failure occurred.
