Hydrogen Embrittlement of 25Cr duplex stainless steel exposed to well fluid with H2S - effect of cold working and product form

Abstract

It is known that cold deformation may have detrimental effects on resistance against SulphideStress Cracking/Stress Corrosion Cracking and Hydrogen Induced Stress Cracking. Thoughit is clear that cold deformation should be restricted, it is sometimes necessary due to e.g.reeling installation or cold sizing. However, the most common standards relevant for pipeproduction and fabrication are not specific in how much cold deformation that can be allowed.NACE0175/ISO 15156 and ASME B31.3 allows maximum 5% cold deformation for carbonsteel without subsequent heat treatment, but no limits are given for stainless steels (SS).NORSOK M-101 allows up to 10% cold deformation of austenitic stainless steel (SS)and 5%for duplex SS and Ni alloys, but as this is a standard for structural steel fabrication, thislimit does not consider H2S service.

Testing will be carried out on duplex SS and austenittic SS to get a better understand-ing of limitations on the amount of cold deformation these materials can have in a sourenvironment. 25% Cr duplex SS (wrought) and 22% Cr duplex SS (wrought) will be testedby constant load in NACE Solution A at an elevated temperature of 80oC and H2S-partialpressure of 20kPa. As a base case the materials will be cold deformed to minimum 4.8%deformation before the start of constant load testing. The microstructure of the duplexmaterials will be examined in a Light Optic Microscope (LOM) before and after the initialdeformation and before H2S-exposure, to characterize the ferrite content and the austenitespacing in the materials. If any signs of cracking with the LOM, further investigation witha Scanning Electron Microscope will be done.