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Hydrogen Stress Cracking Resistance Of High Strength Alloys For Subsea Fasteners

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Bolted connections for subsea flanges and other components must be reliable as they are often used for pressure containing components (subsea Christmas trees, connectors …). When possible, the primary choice for bolting is low-alloy steel with a limitation of actual yield strength (135 ksi) and a maximum hardness of 34 HRC to prevent HSC.

Product Number: 51321-16709-SG
Author: Thierry Cassagne, Dominique Thierry
Publication Date: 2021
Industries: Coatings and Linings , Coatings
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Sacrificial aluminum-indium anode cathodic protection is commonly used for protecting offshore and subsea structures. As a consequence, all metallic fasteners are hydrogen charged under high tensile stresses at the thread roots. This means that material selection must prevent the occurrence of hydrogen stress cracking (HSC) under these conditions. For most equipment where low strength fasteners are
sufficient a low alloy steel can be used provided a maximum yield strength and hardness are specified. When higher strength fasteners are required, low alloy steels must be replaced by corrosion resistant alloys which must be qualified with regard to their susceptibility to HSC. In this work, precipitationhardened nickel alloys from API 6ACRA, work hardened austenitic stainless steels and nickel alloys with yield strengths up to 200 ksi (1240 MPa) have been tested under cathodic protection using a specific test methodology. The objective was to quantify their resistance to HSC and identify their limits of use when exposed to cathodic protection. The results are presented and discussed in the light of current knowledge on HSC for subsea fastener applications.

Sacrificial aluminum-indium anode cathodic protection is commonly used for protecting offshore and subsea structures. As a consequence, all metallic fasteners are hydrogen charged under high tensile stresses at the thread roots. This means that material selection must prevent the occurrence of hydrogen stress cracking (HSC) under these conditions. For most equipment where low strength fasteners are
sufficient a low alloy steel can be used provided a maximum yield strength and hardness are specified. When higher strength fasteners are required, low alloy steels must be replaced by corrosion resistant alloys which must be qualified with regard to their susceptibility to HSC. In this work, precipitationhardened nickel alloys from API 6ACRA, work hardened austenitic stainless steels and nickel alloys with yield strengths up to 200 ksi (1240 MPa) have been tested under cathodic protection using a specific test methodology. The objective was to quantify their resistance to HSC and identify their limits of use when exposed to cathodic protection. The results are presented and discussed in the light of current knowledge on HSC for subsea fastener applications.

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Picture for 04151 High Strength Fasteners for Subsea
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04151 High Strength Fasteners for Subsea Applications

Product Number: 51300-04151-SG
ISBN: 04151 2004 CP
Author: Khlefa A. Esaklul, BP Exploration; John W. Martin, BP Amoco
Publication Date: 2004
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Laboratory testing to qualify several materials for high strength fastener applications for two projects has shown that, in the presence of cathodic protection, nickel alloys 718 and 725 offer the best resistance to hydrogen embrittlement and are available in the strength/size required for high pressure and moderate temperature applications for sub-sea applications.

 
Picture for A Fracture Mechanics Approach To Characterizing Hydrogen Embrittlement Of Fasteners
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A Fracture Mechanics Approach To Characterizing Hydrogen Embrittlement Of Fasteners

Product Number: 51321-16798-SG
Author: Herman E. Amaya, Behrang Fahimi, Ramgopal Thodla
Publication Date: 2021
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Materials properties that are used in specific oil and gas environments are de-rated due to the risks associated with hydrogen embrittlement cracking. In oil production environments the concern is for the onset of stress corrosion cracking (SCC), while in seawater environments the concern is for Hydrogen Induced Stress Cracking (HISC). Both are hydrogen embrittlement phenomena with the distinction being the source of hydrogen for each. In SSC the source of hydrogen is from the presence of H2S in the oil production fluids, and in HISC the source of hydrogen is from the dissociation of water from the cathodic protection system. This paper is focused on the latter phenomena and aims to characterize the susceptibility of carbon alloy steels as applied in fastener applications, in a seawater environment under cathodic protection.
Picture for 03017 A review of offshore experiences with bolts and fastenner
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03017 A review of offshore experiences with bolts and fasteners

Product Number: 51300-03017-SG
ISBN: 03017 2003 CP
Author: Karl P. Fischer
Publication Date: 2003
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A joint industry project "Corrosion protection and maintenance of bolting and fasteners" was initiated in 2001. The main part of the project is a 10 year testing program of pretensioned stud bolts in the marine atmospheric zone, splash zone and submerged zone in Norway and in the US.
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