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After a number of failures in the Oil and Gas industry research works on hydrogen embrittlement (HE) of nickel-based alloys has been quite significant. Much work had been done previously in other industries, nuclear and aeronautic in particular. Despite this work, a lot remains to be understood. Among them, precipitation-hardened (PH) nickel alloys UNS N07718 has been significantly studied and its HE resistance is now better assessed based on its microstructure. Less work has been performed on some of the other PH nickel alloys,although, their HE resistance is better appreciated from recent literature data. The results published at NACE Corrosion 2019 from a large JIP study indicated that PH nickel alloys could be split in three families with less susceptible alloys, like UNS N07718, UNS N09925 and UNS N09935, more susceptible alloys like UNS N07725 and UNS N07716, while alloy UNS N09945 had variable susceptibility. Besides PH nickel alloys, other solution-annealed or cold worked alloys are used in environments where hydrogen can be present. As PH alloys they are also susceptible to HE, but published studies are scarce. This paper is a review of internal and published work setting the base of our current understanding on the HE resistance of various PH, solution annealed and cold worked nickel-based alloys. Consequences on the use of these alloys are discussed for Oil and Gas applications.
The high strength and corrosion resistance of nickel-chromium alloys such as Alloy 718 and nickel-iron-chromium alloys such as Alloys 945 and 945X make them particularly good candidates for use in demanding environments in the upstream oil and gas industry. These materials generally perform well where resistance to sulphide stress cracking and chloride stress corrosion cracking is required. However whilst these alloys are considered ‘NACE compliant' environmentally-assisted failures can still occur.It is generally accepted that for hydrogen cracks to initiate there must be a critical combination of stress susceptible microstructure and hydrogen concentration. In this project the effect of microstructure is explored by heat treating Alloy 718 945 and 945X to standard and non-standard conditions. Tensile specimens were slow-strain-rate-tested in air and under CP to explore sensitivity to hydrogen embrittlement. Finally the effect of a severe stress concentration in the form of a sharp notch was used to determine whether there is an enhanced susceptibility to hydrogen embrittlement due to the presence of local stress raisers. The results are compared with tests undertaken by other authors under various hydrogen-charging conditions.
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This paper presents work in follow-up to the previous study. It is focused on UNS1 N07718, UNS N09925, UNS N07725 and UNS N09946. A series of incremental step load tests of compact tensile specimens were conducted to measure the fracture toughness during testing and cracking was monitored by the Electric Crack Growth Monitoring technique. A new engineering technique, referred to as statistical fractography, was used to investigate the fracture surface morphology and extract from it the fracture properties of the alloys.
In a 1998 study, costs for corrosion in USA were estimated to be about 276 billion US-$. One way to reduce this gigantic amount of money is to use modern stainless steels and nickel alloys with excellent resistance to various forms of corrosion in corrosive environments like seawater, brines, oil and sour gas wells.