Case-History of Environmental Cracking Failures with Alloy K-500 for Downhole Completion Tools

The industry saw a wide use of K-500 material for downhole completion tools in early to mid-1980's. However, certain field experiences which resulted in failure of some downhole components were observed with K-500, which caused most users to shift away from K-500 in favor of other nickel alloys. Recently, there has been a renewed interest to extend the performance limits of K-500 in MR0175/15156-3.  Committee discussion during the ballot process suggested there was very little detail to past experience. This paper will present two case histories never published from early 1980's where K-500 experienced failures as downhole equipment. The first case is about a sub-surface safety valve which failed after two years of service in a well having high H₂S content. The second case deals with the failures and/or deterioration of several downhole tools in multiple wells from nearby fields with small but varying contents of H₂S combined with CO₂ content. Discussion during the ballot also indicated that possibly all past failures were limited to one melt practice. The raw materials for these cases were from several heats produced by different sources and melting practices. This paper puts forward the field conditions associated with the failures and the analysis performed.