09298 Sulphide Stress Cracking (SSC) Resistance of 13% Cr and Super 13% Cr Stainless Steels below pH 3.5 In Low H2S Environment

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Product Number: 51300-09298-SG

ISBN: 09298 2009 CP

Author: Suchada Punpruk, Siriporn Daopiset and Yves Gunaltun

Publication Date: 2009

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According to the NACE MR0175/ISO15156 Standard, the use of martensitic stainless steels is limited to H2S partial pressure of 0.1 bar (0.01 MPa) for pH values above 3.5. However, the steels were successfully used in Field A up to 0.0145 bar (0.00145 MPa) H2S partial pressure at pH below 3.5. It was decided to check the possibility to extend the domain of its use up to 0.035 bar (0.0035 MPa) H2S partial pressure at pH 3-3.2 (Field B conditions) and then up to 0.05 bar (0.005 MPa) H2S partial pressure at the same pH (Field C conditions). Sulphide stress cracking (SSC) resistance of martensitic stainless steel and super martensitic stainless steel were duplicated in two independent laboratories. In one of the laboratories, test samples were placed in both liquid phase and gas phase under condensing conditions. In parallel, H2S concentration variations along the top part of the tubing during shut-in conditions were measured in one well. The paper summarises SSC results on martensitic and super martensitic stainless steels under the conditions of Field B and Field C, in liquid and gas phases, and evaluate the SSC severity during shut-in conditions considering the H2S evolution in gas wells. The tests confirm the suitability of one grade of super martensitic stainless steel (super 13% Cr C95 grade) up to 0.05 bar (0.005 MPa) H2S partial pressure at pH 3-3.2 and martensitic stainless steel (13% Cr L80 grade) up to 0.035 bar (0.0035 MPa) H2S partial pressure at the same pH in case of no chloride. Possible reasons for the successful use of 13% Cr steel in the field A are summarised.

KEY WORDS: Martensitic stainless steel, Super martensitic stainless steel, 13% Cr steel, Super 13% Cr steel, sour service, Sulphide stress cracking, Stress corrosion cracking, H2S partial pressure, chloride