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Hydrogen Embrittlement Susceptibility in Corrosion Resistant Materials for Fasteners

Product Number: 51323-18763-SG
Author: Hans Husby, Inge Morten Kulbotten, Gisle Rørvik
Publication Date: 2023
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In some cases, the materials selection for subsea fasteners requires resistance to corrosion in seawater and, also, adequate hydrogen embrittlement (HE) resistance due to plausible connection to the cathodic protection system. In this work, selected materials were subject to incremental step loading testing under cathodic protection polarization in 3.5 wt% NaCl solution. Testing of 6 individual heats of Alloy 716 (UNS N07716) and 725 (UNS N07725) showed poor HE resistance for several heats, and a worse performance for all heats than a single tested heat of Alloy 718 (UNS N07718) which was included for comparison. Four heats of Alloy 625 (UNS N06625) showed quite varying microstructures, mechanical properties, and, also, HE resistances – with some HE resistances possibly below preferred levels for fastener applications. Two tested strain hardened austenitic materials were Alloy 830 (UNS N08830) and P750 (DIN 1.4675), that both had high fracture stresses considering the materials high yield strengths around 1200 MPa and they are candidate materials for subsea fasteners. A low alloy steel B7 material, included as a reference, showed high HE resistance, but the test method used herein should be modified when testing materials with high yield to tensile strength ratios.

In some cases, the materials selection for subsea fasteners requires resistance to corrosion in seawater and, also, adequate hydrogen embrittlement (HE) resistance due to plausible connection to the cathodic protection system. In this work, selected materials were subject to incremental step loading testing under cathodic protection polarization in 3.5 wt% NaCl solution. Testing of 6 individual heats of Alloy 716 (UNS N07716) and 725 (UNS N07725) showed poor HE resistance for several heats, and a worse performance for all heats than a single tested heat of Alloy 718 (UNS N07718) which was included for comparison. Four heats of Alloy 625 (UNS N06625) showed quite varying microstructures, mechanical properties, and, also, HE resistances – with some HE resistances possibly below preferred levels for fastener applications. Two tested strain hardened austenitic materials were Alloy 830 (UNS N08830) and P750 (DIN 1.4675), that both had high fracture stresses considering the materials high yield strengths around 1200 MPa and they are candidate materials for subsea fasteners. A low alloy steel B7 material, included as a reference, showed high HE resistance, but the test method used herein should be modified when testing materials with high yield to tensile strength ratios.

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Correlation Of Hydrogen Diffusion And Trapping Behaviour With Hydrogen Embrittlement Resistance In Line Pipe Steels

Product Number: 51321-16564-SG
Author: Ali Smith/ Philippe Darcis/ Emanuele Paravicini Bagliani
Publication Date: 2021
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