ABSTRACT

13Cr Super Martensitic Stainless Steel (SMSS) with a specified minimum yield (SMYS) of 110 ksi is commonly used in the Oil & Gas industry.

The present work has been aimed at evaluating the influence of different heat treatment processes on the corrosion resistance of 110 ksi 13Cr SMSS. Bars were produced with a conventional Qt process in gas fired batch furnaces as well as on an integrated forging line with inductive re-heating and direct quenching. The bars were tested according to NACE TM0177 Method A to prove the resistance to SSC. Tests were performed in several environments with different Chloride concentrations, pH levels and H2S partial pressures from 0.01 up to 0.05 bar. First results confirm the potential of new production concepts for SMSS steel bar products.

INTRODUCTION

Due to the combination of high strength and corrosions resistance 13Cr Super Martensitic Stainless Steels (SMSS) with specified minimum yield strength (SMYS) of 110 ksi are used commonly in the Oil & Gas industry. In NACE MR0175 / ISO 15156-3 1 only 13Cr SMSS (UNS (1) S41425, UNS S41426 and UNS S41427) at hardness levels corresponding to 95 ksi specified minimum yield strength (SMYS) are covered. Nevertheless, there is a regular demand for 13Cr SMSS with minimum 110 ksi yield strength from the Oil & Gas industry.

In 2005 the sulfide stress cracking (SSC) resistance of forged 13Cr SMSS 110 ksi bar stock under different chloride concentration, pH and H2S partial pressure was published. Application limits for this material were defined. 2

Further trials with increasing chloride concentrations but lower pH were done with 13Cr OCTG tubing material. The ‘no SSC’ domain for 110 ksi grade super 13Cr steel (UNS 41426) has been proposed as a function of Cl- concentration, pH and H2S partial pressure. The influence of Cl- concentration was larger for the lower pH or for the higher H2S partial pressure environments. 3

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