Galvanised Bolts on 316L Piping System

[Angsi]

I have another unusual question. Is the use of galvanised cs bolts (A193)acceptable on SS (316L) piping system in view of zinc embrittlement during fire etc?

The second question, is cadmium plated flurorocarbon coated bolts better in terms of performance/durability in an offshore marine environment compared to galvnised bolts?

Thanks in advance.

 

[Metalguy]

Look up the "Flixbourogh" sp? disaster in England some years ago. Involved SS piping filled with rocket fuel (cyclohexane, IIRC) and a fire. All was OK until the galvanized sheet metal on the roof got hot enough to drip liquid zinc on the red hot SS pipes. Expensive way to make a big hole in the ground----.

 

[SJones]

1st Answer: No

2nd answer: Industry is beginning to shy away from cadmium owing to HSE concerns. As to whether fluorocarbon is any good, it will depend on the skills of the fitters employed and the number of times the joints need to be made and broke.

Steve Jones
Materials & Corrosion Engineer

http://www.pdo.co.om/pdo/

 

[mshimko]

Using zinc coated (galvanized) bolting on stainless steel is not recommended: adverse area effect will rapidly consume the zinc and then deteriorate the bolting.

As to what I would recommend - the answer depends on the system, the environment, and the piping system material. Often monel alloys are recommended for immersion or splash zones; and CRES for topside applications, but more specifics may be needed to verify these very general recommendations.

 

[EdStainless]

as Mshimko said, it largely a function of how wet the area is. In places that are rarely wet galv should work. If they are only wet occasionally then stainless bolts should be OK. If they will see seawater regularly then a Ni alloy is in order. Monel bolts are common, so are some other Ni alloys.

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Corrosion never sleeps, but it can be managed.

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