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Material requirements used in subsea environment?

asked Jul 25, 2016 in Material by GioTalbott (545 points)
Some rules of thumb to use when selecting materials to be used in the subsea environment.

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answered Jul 25, 2016 by GioTalbott (545 points)
Materials used in the subsea equipment should conform to relevant regulations, industry standards, and codes.

In general term, material selection, coating, and corrosion protection for subsea systems should be designed for life of field. Materials should be suitable for use in seawater in the presence of a cathodic protection system and those exposed to seawater should be suitable for the purpose. The intent is for materials to conform to NACE MR0175, where feasible with adequate ductility to resist fatigue and brittle failures.  Consideration should be given to the carbon equivalent for ease of welding and to minimize fabrication problems.

In term of compatibility and construction, materials selected should be galvanically compatible. Construction should be seamless, unless not practical or otherwise specified. Materials selected should be compatible with all project fluids and chemicals they come into contact with. 17-4 ph material should not be used for valve stems or anywhere it comes into contact with seawater.

Special precautions should be used for Inconel 718 and cladding that is subsequently subjected to tensile forces.
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answered Jul 26, 2016 by GioTalbott (545 points)
Materials used for pressure containing or pressure controlling components should be compatible with the specified fluids.

Ring grooves, seat pockets, and metal seal surfaces should be inlaid with Inconel 625, unless the parent material is of sufficient corrosion resistant alloy (CRA) type. Materials should provide the necessary corrosion and erosion resistance.

The product specification level (PSL) referenced in API SPEC 17D for all hydrocarbon-wetted bore pressure containing equipment should be PSL 3, including Charpy Impact tests at 0°F, per API SPEC 6A (e.g., tree body, tree cap, choke systems, tubing hanger, valve bodies, connectors, etc.).  All other components and pressure containing assemblies should be to PSL 2.

Valve testing requirements should be PSL 3 with gas testing.  All other components and pressure containing assemblies, including final stack up of the tree assembly, should be to PSL 2, through FAT. All valve components, tree assemblies and other equipment (where applicable) should be API monogrammed 17D, PSL3.