Precipitation-hardened nickel-based alloys have been used for decades in the oil and gas industry. Among these alloys, UNS1 N07718 has received the most attention for use in upstream applications such as tubing hangers, production stab plate, multiphase flowmeter bodies, and valve stems because of its performance in sour wellbore fluids (SWFs) and hydrogen-charging environments.
Low alloy steels (LASs) combine relatively low cost with exceptional mechanical properties, making LASs commonplace in Oil and Gas equipment. However, the strength and hardness of LASs for sour environments and for applications that generate atomic hydrogen at the surface, e.g., cathodic protection, is limited to prevent different forms of hydrogen embrittlement (HE) such as hydrogen stress cracking (HSC) and sulfide stress cracking (SSC). As a result, the specified minimum yield strength (SMYS) of forged LASs for, e.g., subsea components, rarely exceeds 550 MPa (80 ksi), while the most common pipeline steels are API(1) X65 to X70, with a SMYS of 450 MPa (65 ksi) and 482 MPa (70 ksi), respectively. Moreover, ISO(2) 15156-2 restricts LASs to a maximum of 1.0 wt% Ni due to SSC concerns. The LASs that exceed the ISO 15156-2 limit have to be qualified for service, lowering their commercial appeal.
In this work, the HSC resistance of the high-nickel (3.41 wt%), quenched and tempered (Q&T), nuclear-grade ASTM(3) A508 Gr.4N LAS was investigated using slow strain rate testing (SSRT) as a function of applied cathodic potential. Results showed that the yield strength (YS) and ultimate tensile strength (UTS) were unaffected by hydrogen, even at a high negative potential of -2.0 VAg/AgCl. HE effects were observed once the material started necking, manifested by a loss in ductility with increasing applied cathodic potentials. Indeed, A508 Gr.4N was less affected by H at high cathodic potentials than a low-strength (YS = 340 MPa) ferritic-pearlitic LAS of similar nickel content. SSRT results were linked to microstructure features, which were characterized by light optical microscopy (LOM), scanning electron microscopy (SEM) coupled to electron backscatter diffraction (EBSD).
NEW TITLE AVAILABLE NOW!! The main objective for Dr. Ali Morshed's new book, A Practical Guide to Microbiologically Influenced Corrosion (MIC) in the Upstream Oil & Gas Sector, was to produce a practical MIC guide to facilitate the identification, monitoring, assessment, and control of bacterial activity and MIC that might arise within assets associated with the upstream oil and gas sector.
“Practical” refers to content that can be readily related to various bacterial and MIC scenarios, which are likely to arise for any upstream operator and (a content which) can be easily used to resolve, rectify, or improve such MIC scenarios.
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Five relevant and informative case studies are also included.
2023 AMPP, 114 pgs
New for 2018! This NACE International state-of-the-art report contains information about materials that provide a corrosion-resistant alternative to plain carbon steel reinforcing bar (rebar). The report is intended for use by engineers when considering the use of alternative concrete reinforcement and post- or prestressing strand materials with higher corrosion resistance than that of conventional carbon steel alloys.