NDLI: Fasteners in Subsea Applications: End User Experiences and Requirements

Content Provider	The American Society of Mechanical Engineers (ASME) Digital Collection
Author	Rørvik, Gisle Haaland, Bjørnar Øvrum Kirkemo, Finn
Copyright Year	2014
Abstract	Fasteners used for critical applications subsea represent a challenge in terms of material selection, quality control, traceability and documentation for manufacture and delivery to ensure adequate performance, integrity and avoidance of costly failures. The definition of critical subsea fasteners are both pressure containing and primary load bearing members, but may in a wider sense also include fasteners which may affect functionality of valves, equipment and instruments for safe, reliable and cost effective operation. The major failure mechanism experienced during the last decades is so-called hydrogen induced stress cracking (HISC) or hydrogen embrittlement (HE) primarily resulting from the hydrogen charging conditions of the cathodic protection (CP) system. The main bulk of fasteners used subsea is of low alloyed steel grade type (e.g. ASTM 320 Grade L7, L7M, L43 bolts with ASTM 194 Grade 4, 7M, 7 nuts) which relies on electrical continuity to the cathodic protection system to avoid sea water corrosion, but may be prone to HISC/HE if the fastener hardness and strength level exceed the specified and established limits. If higher strength materials are needed from design, either cold formed or precipitation hardened CRA’s are usually selected (e.g. Grade 59, 660, 625, 686, 718, 725), but these may also be susceptible to HISC/HE depending on strength level and manufacturing practice. The present paper will give some field experience and typical examples of recent HISC failure case histories for low alloyed steel grades, but also for some CRA type of subsea fasteners. Furthermore, some in-house low alloyed steel grade (L7, L43) fastener HISC test results will be presented to indicate the robustness of today’s hardness and strength level restrictions, and at which loading and pre-tension level a given strength grade may be prone to HISC failure. Finally, some experience from manufacturing stage as well as focus areas in materials specification, quality assurance / quality control and design will be discussed.
Sponsorship	Ocean, Offshore and Arctic Engineering Division
File Format	PDF
ISBN	9780791845455
DOI	10.1115/OMAE2014-24520
Volume Number	Volume 5: Materials Technology; Petroleum Technology
Conference Proceedings	ASME 2014 33rd International Conference on Ocean, Offshore and Arctic Engineering
Language	English
Publisher Date	2014-06-08
Publisher Place	San Francisco, California, USA
Access Restriction	Subscribed
Subject Keyword	Cathodic protection Hydrogen Bearings Fasteners Instrumentation Valves Precipitation hardening Astm international Design Robustness Tension Manufacturing Failure Hydrogen embrittlement Failure mechanisms Seawater Cracking (materials) Steel Pressure Stress Strength (materials) Fracture (process) Corrosion Quality control Ocean engineering
Content Type	Text
Resource Type	Article

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