Extended Use of S13Cr Materials for Downhole Production Tubing

Abstract

Abstract Historically, martensitic stainless steels (13Cr or Super 13Cr) are known to provide a high strength, corrosion resistant production tubing material for sweet (CO2) corrosion service. The material is generally considered to be susceptible to Sulphide Stress Cracking (SSC) in sour (H2S) production environments. However, the combination of pH, temperature and chloride levels plays a significant role in altering the behaviour of this material under sour conditions. pH is commonly known to be affected by factors such as bicarbonate buffering, the presence of carbon dioxide and acids. The "self-healing" rate of chromium oxide of stainless steels is dependent upon the environment to which it is exposed, affecting its resistance to SSC. By understanding the overall service conditions and testing the martensitic stainless steels material(s) accordingly, the use of this material has been made possible beyond commonly accepted limits without compromising its overall properties. Specific testing (cyclic slow strain rate tests), more onerous than that recommended by NACE, has been conducted for the qualification of identified martensitic stainless steels. The test regime covered both production and shut-in conditions. The results show that under the particular conditions, S13Cr materials cracking resistance differs from the limitations described by NACE MR0175/ ISO 15156. This paper aims to highlight business cases that have led to specific testing of martensitic stainless steel and describes the significant cost savings that have been achieved by using S13Cr materials as production tubing in sour service.