51315-5510-Developments on a Modified 1.4418 Stainless Steel for the Oil and Gas Industry

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Product Number: 51315-5510-SG

ISBN: 5510 2015 CP

Author: Martin Monnot

Publication Date: 2015

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Due to their good corrosion resistance as well as a wide range of mechanical properties super martensitic stainless steels are generally used in the petrochemical industry. One example of these materials is the precipitation hardening martensitic grade EN 1.4542 (UNS17400 -17-4 PH) which is largely used in oil & gas applications for wellheadand valve components. However this material showed some environmental cracking problems in service. Therefore the NACETG 299 has been discussing the utilization limits listed in the NACE standard MR0175 for this material.In this context the super martensitic stainless steel EN 1.4418 (15% Cr -5% Ni - 0.8%Mo) which presents good corrosion and mechanical properties could be a candidate grade to replace the 17-4 PH SS in petrochemical applications. In this work the role of different alloying elements on the 1.4418 composition such as Mo W Cu and Nbiselectrochemically and metallurgically discussed in order to determine the optimal chemical composition of this material for oil & gas environments.Therefore this study is based on laboratory stainless steel heats for which the chemical composition was strictly controlled.The corrosion mechanisms for the modified 1.4418are discussed in terms of pitting corrosion sulfide stress cracking repassivation processes and in comparison with those found the 17-4 PH. Moreover the effect of H2S on 1.4418 corrosion propertieshasbeen directly associated different chemical compositions and with the metallurgical investigation.Keywords: Martensitic Stainless Steels Sulfide Stress Cracking Pitting Corrosion and Alloying Elements Effect