Why replace carbon steel bolts with Stainless Steel 1

[Tweetybird]

Auditor insisting all carbon steel bolts be replaced with stainless on SS code vessels, but I have not got a definitive answer why?
Talking thousands of carbon bolts ($$$) that have been in service with no problem for years. I must be missing something
Any dialogue would be appreciated.

 

[JohnRBaker]

Is this an application where food products would be present? In a past life I designed capital machinery for the baking industry (mostly automated production of pan bread) and while we generally were able to get away with zinc- and nickle-plated fasteners, we occasionally were forced to use stainless steel where there might be some corrosive action, such as dough mixers and inside of ovens or where wash-down and sanitation was an issue.

John R. Baker, P.E.
Product 'Evangelist'
Product Engineering Software
Siemens PLM Software Inc.
Digital Factory
Cypress, CA
Siemens PLM:
UG/NX Museum:

To an Engineer, the glass is twice as big as it needs to be.

 

[MintJulep]

Auditors generally are required to audit against something. A spec, a standard, a drawing...

If he can't cite a specific violation or non-compliance just tell him to go away.

Also, it's unusual for an audit process to direct a "corrective action". Typically the audit identifies "findings", and the auditee responds with the corrective action, which may be "it's fine as it it."

 

[moltenmetal]

There are plenty of reasons NOT to use SS fasteners on SS code vessels and code piping: cost, lower stress values, risk of galling and risk of Cl stress cracking. We almost never do- our standard for flange fasteners is B7/2H, zinc coated for < 400 F and black oxide finish for 400-800 F. Some customers want the Zn replaced with a fluoropolymer coating (i.e. Xylan).

There are a few reasons to consider SS fasteners:

1) External corrosion conditions, where you're worried about the CS fasteners being eaten either directly or as a result of galvanic corrosion.
2) Concerns about contamination of the stainless steel surface by contact with the carbon steel, leading to premature corrosion of the stainless steel. This is usually a dumb one- not really a concern.
3) Very high temperature operation, where the temperature limits of the CS fasteners are exceeded.
4) Surface cleanliness/cleanability for high purity applications

No inspector should be telling you what needs to be used without a reference.

 

[Tweetybird]

I concur with your reply. Just needed input. Really appreciate the bullet points
the max plant temp is 450 F but seldom runs at that high of temp.

 

[Tweetybird]

Thanks for some input. The plant is a chemical process plant for refining toxic waste. No food products. Low pressures <300psi; high temp of 450F