Alloy K-500 saw widespread use as a high strength material for sour service in the oil field up to the mid-1980s. Its use declined after that, however, following field failures that were published in the literature of wellhead stems, subsea bolts, and drill stem tools. These failures appear to be unrelated to sour service. In the authors’ company, unpublicized failures of downhole tools made from Alloy K-500 were observed in sour service, causing the company to abandon Alloy K-500 for downhole tools in favor of other nickel alloys. As evidenced by the ballot to the NACE/ISO Maintenance Panel to extend the performance limits of Alloy K-500 in NACE MR0175 / ISO 15156-3A, it is obvious that there has been renewed interest by the industry in Alloy K-500. This ballot was based upon laboratory testing, and two attempts at passing the ballot failed. Committee discussion during the balloting suggested there was insufficient detail in the past field experience to compare directly with the laboratory data, and questions were also raised concerning the melt practice and metallurgical condition of the material that had failed in the field. These issues prompted the authors to conduct a historical review of their company’s past failures with the alloy. This paper will present three case histories from the early 1980's where Alloy K-500 experienced failures in downhole equipment. The intent of the paper is to put forward the field conditions under which the failures were seen and report the analysis done on the failed components. This could help the reader better understand the issues facing the use of Alloy K-500 alloy for downhole completion tools and shed additional light on the Maintenance Panel’s decision to reject a ballot for extended limits in NACE MR0175 / ISO 15156-3.

Subject
Test methods, Energy dispersive X-ray spectroscopy, Corrosion failures, Materials, Corrosion resistant alloys, Valves, Nickel based alloys, Fracture surfaces, Tools, Monel alloys, Fracture, Alloys, Hydrogen
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2009
Association for Materials Protection and Performance (AMPP)
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