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Hydrogen Embrittlement Resistance of Oil Patch Alloy 718 and Its Correlation to the Microstructure

Picture for Hydrogen Embrittlement Resistance of Oil Patch Alloy 718 and Its Correlation to the Microstructure
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Product Number: 51321-16393-SG
Author: Julia Botinha/Bodo Gehrmann/Helena Alves
Publication Date: 2021
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$20.00
$20.00

Alloy UNS N07718 (known as Alloy 718) is a precipitation hardening nickel alloy containing additions of chromium, niobium, titanium, aluminum and molybdenum. This combination of elements provides an alloy with a combination of high yield strength and corrosion resistance required in sour service applications. Through the precipitation hardening heat treatment, the alloy precipitates the intermetallic Gamma Prime (ordered fcc Ni3Al) and Gamma Double Prime (bcc tetragonal Ni3Nb) phases, which are responsible for elevating the yield strength of the material. Additionally to the importance of these both phases in the hardening process, previous studies showed that the microstructure of Alloy 718 may also have a direct influence on its susceptibility to Hydrogen Embrittlement. Laboratory melts with modified compositions based on Alloy UNS N07718 were produced and tested to correlate both mechanical and hydrogen embrittlement properties. The testing plan included mechanical testing, Slow Strain Rate Tensile (SSRT) tests under cathodic protection and numerical thermodynamic simulations.

Key words: Nickel alloys, Corrosion Mechanisms, UNS N07718, Alloy 718, Hydrogen Embrittlement, Neutron Diffraction, Hardening Phases, Slow Strain Rate Tensile Test, Oil and Gas industry

Alloy UNS N07718 (known as Alloy 718) is a precipitation hardening nickel alloy containing additions of chromium, niobium, titanium, aluminum and molybdenum. This combination of elements provides an alloy with a combination of high yield strength and corrosion resistance required in sour service applications. Through the precipitation hardening heat treatment, the alloy precipitates the intermetallic Gamma Prime (ordered fcc Ni3Al) and Gamma Double Prime (bcc tetragonal Ni3Nb) phases, which are responsible for elevating the yield strength of the material. Additionally to the importance of these both phases in the hardening process, previous studies showed that the microstructure of Alloy 718 may also have a direct influence on its susceptibility to Hydrogen Embrittlement. Laboratory melts with modified compositions based on Alloy UNS N07718 were produced and tested to correlate both mechanical and hydrogen embrittlement properties. The testing plan included mechanical testing, Slow Strain Rate Tensile (SSRT) tests under cathodic protection and numerical thermodynamic simulations.

Key words: Nickel alloys, Corrosion Mechanisms, UNS N07718, Alloy 718, Hydrogen Embrittlement, Neutron Diffraction, Hardening Phases, Slow Strain Rate Tensile Test, Oil and Gas industry

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Hydrogen Embrittlement of High Strength Precipitation Hardenable Nickel Alloys

Product Number: 51319-13161-SG
Author: Michael Dodge
Publication Date: 2019
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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.
Picture for Comparison Of Hydrogen Embrittlement Testing Methods Of Alloy 718
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Comparison Of Hydrogen Embrittlement Testing Methods Of Alloy 718

Product Number: 51321-16821-SG
Author: Brian Kagay; Stevew Coryell; Kip Findlet; Steve McCoy
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Picture for Hydrogen Embrittlement of Additively Manufactured Inconel 718
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Hydrogen Embrittlement of Additively Manufactured Inconel 718

Product Number: 51319-13453-SG
Author: Liu Cao
Publication Date: 2019
$20.00

Precipitation hardenable nickel alloys are commonly used in oil and gas offshore structures where requires outstanding mechanical strength and corrosion resistance. In seawater galvanic coupling to steel or cathodic protection promotes the formation of atomic hydrogen on the surface of Inconel 718. Hydrogen atoms further dissolve into the metal matrix and cause hydrogen embrittlement. The unconventional Additive Manufacturing (AM) process generates fine microstructure and alters surface finish that affect hydrogen intake process and the subsequent hydrogen embrittlement. The effects of hydrogen embrittlement are investigated on different build orientations and surface finish of AM Inconel 718 by slow strain rate (SSR) testing in seawater environment under cathodic protection. The susceptibility of AM 718 to hydrogen embrittlement is discussed based on the SSR results and metallography analysis with respect to its wrought counterpart.
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