Stainless Pipes + CS Stud & Nuts + Coastal Rain = Corroded Studs

[racookpe1978]

Fluid = Hot fuel gas at 410 Deg F, modest pressure (about 225 psig). Flanges are insulated with wrap-around pads, so they are not watertight, not under a solid sheetmetal cover.
Stainless pipe and Class 600 A182/F304 flanges with Flexitallic Gasket, pipe-pipe electrical connectivity is pretty good.
carbon steel B7 studs with 8GR 2H nuts.

The flanges are installed under an open area in coastal FL just off the Intercoastal Waterway, so modest salt but significant rain exposure.
Every flange is corroding rapidly, as you would expect, even those exposed for only a few weeks.

What is a better material for the studs and nuts?

 

[gerhardl]

Coastal experience from Northern Europe (Scandinavia/Norway): flanges bolt and nuts exposed whole and partly to coastal atmosphere will corrode unless at least similar stainless quality as the pipeline.

 

[Dhurjati Sen]

Dear racookpe1978,

Absolutely agree with gerhardl.

Change the MOC in the relevant drawings, change the same in manuals and standards of your organisation and current / future purchase orders.

Note that this is a serious design error and could be taken up at the designer level.

Regards.

DHURJATI SEN

https://www.nace.org/people/dhurjatisen

 

[MJCronin]

I agree with the two comments above ....

This is a serious, expensive newbie error that an experienced piping engineer would not make. When MBAs assign people with zero experience to a project, this kind of thing will happen !!

Another alternative to consider in this semi-marine environment is PTFE coated carbon steel fasteners.

https://www.eng-tips.com/viewthread.cfm?qid=325662

https://www.whitfordww.com/

MJCronin
Sr. Process Engineer