51312-01593-Low Stress Connection Design versus Environmental Cracking in Corrosive Well Service Conditions

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Product Number: 51312-01593-SG

ISBN: 01593 2012 CP

Author: Russell D. Kane

Publication Date: 2012

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Horizons for oil and gas production are progressing deeper and into higher pressure formations that require higher strength particularly for oil country tubular goods (OCTG). Concomitant factors in these wells are higher H2S and CO2 partial pressures that require more corrosion resistant alloys. For many deep wells martensitic and duplex stainless steels are the materials of choice due to their combination of corrosion resistance strength and cost. In most cases susceptibility to environmental cracking (e.g. sulfide stress cracking and stress corrosion cracking) is looked upon as a metallurgical property that is defined principally by the materials processing history microstructure alloy content and strength. However just as important are the stresses developed in the threaded connection as connections are usually the most highly stressed location and source of a majority of downhole failures in OCTG. This paper addresses the results of an exploratory full scale testing program that evaluated the resistance of two different connection types (thread-and-couple and integral arrangements) on 13Cr stainless steel production tubing exposed to simulated sour service conditions (0.15 to 15 psia H2S). After the completion of testing a detailed analysis of failed samples was performed to identify the location of failure and fracture modes. The results are discussed in terms of resistance of 13Cr OCTG to environmental cracking in downhole service applications.