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Stainless Bolting

Stainless Bolting

I was wondering if anyone could give some advice on what is the best stainless bolting material for long term subsea use in a CP environment. Basically I am required to bolt to a M20 female threaded component made from 431S29 (UNS S43100). I was thinking of using the same material but was unsure of its performance subsea. If I was to use another grade of bolt the female thread would still be 431 and I am most likely stuck with this anyway. Any advice would be much appreciated.

Thank you.

RE: Stainless Bolting

It depends on things including temperature, depth (oxygen content), whether or not it may be exposed to sour production fluids or not, CP voltage, etc. On the least demanding end 316 can be used. Better than that are the super-austenitics (e.g. A286). If highest performance is needed you can move to nickel alloys. I would, however shy away from duplex and super duplex bolting, as these materials are notorious for having low impact resistance if not formed/heat treated properly. After all, if it's going subsea you would hate to scrimp on bolting only to have to pull the equipment back up to replace.

RE: Stainless Bolting

So you are saying I may be ok screwing 316l bolts into the 431 if the environment isnt subject to other potential contaminents? The componet is part of a cable connection system in shallow water depths of about 30m at 30 degrees C, in free flowing seawater. I wouldnt really expect there to be many if any contaminents.

RE: Stainless Bolting

430 might not be the best choice, both from a hydrogen embrittlement and a galling point of view. Probably best to stick with an austenitic alloy and ensure a hardness differential of minimum 50 HRB, unless disassembly is not an issue.

Steve Jones
Materials & Corrosion Engineer

All answers are personal opinions only and are in no way connected with any employer.

RE: Stainless Bolting

Same goes for martensitic 431 rednose

Steve Jones
Materials & Corrosion Engineer

All answers are personal opinions only and are in no way connected with any employer.

RE: Stainless Bolting

ISO3506 A4-70 or 80.

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