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Hydrogen Embrittlement Susceptibility in Corrosion Resistant Materials for Fasteners

Picture for Hydrogen Embrittlement Susceptibility in Corrosion Resistant Materials for Fasteners
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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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Hydrogen Embrittlement of SS316L Instrument Tubing in a Hydroprocessing Unit

Product Number: 51320-14357-SG
Author: Siew Leong Waia, Rajaram Chidambaramb, John Richertc, Jorge Perdomo
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An unexpected failure of 316L Stainless Steel instrument tubing occurred in a high pressure Hydroprocessing unit resulting in a shutdown of the unit. The tubing system consisted of a compression type fitting commonly used in instrument systems and had only been in service for 3 years when the failure occurred. The failed tubing samples were removed for metallurgical analysis and determination of damage mechanism.   

Metallurgical analysis and finite element analysis of the tubing identified excessive cold working leading to hydrogen embrittlement as the primary mode of failure. This paper details the investigation into the failure to arrive at the root cause and the preventive measures adopted to assess the installed population of tubing in similar service.  

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

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Picture for Improving Hydrogen Embrittlement Resistance Of Precipitation Hardened Nickel-Alloys
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Improving Hydrogen Embrittlement Resistance Of Precipitation Hardened Nickel-Alloys

Product Number: 51321-16673-SG
Author: Luca Foroni, Carlo Malara
Publication Date: 2021
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Precipitation hardened (PH) Ni-alloys are widely used in the oil and gas industry since they provide an excellent combination of corrosion resistance and mechanical strength. Their use in the manufacture of API1 6A pressure-containing and pressure-controlling components is subject to the stringent requirements of specification API Standard 6ACRA. However, matching the requirements of API Standard 6ACRA does not preclude susceptibility of some PH Ni-alloys to hydrogen embrittlement (HE) and this in some cases has led to premature and unexpected failures of components made from such
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