Carbon Steel Studs and Bolts for SS Fittings

[nickypaliwal]

Our vendors are offering CS studs and Bolts for Valves with SS body. They are supplying the same to our client since quite long.

Also the piping class of our client says CS studs and Bolts. But the details for valves asks for SS studs and Bolts.

For Non-standard valves, we do not have any specification to follow, so we recommend SS studs and bolts.

Can we accept CS studs and Bolts offered by vendors ? Also where can/do we actually go for CS studs/bolts in place of SS in SS/DSS body ?

Is this acceptable for the fittings as well ?

 

[CoryPad]

If the fasteners are not exposed to the same environment, it is possible to use carbon steel fasteners to join stainless steel components. There still is the problem of different thermal expansion coefficients.

 

[nickypaliwal]

But the piping class states CS studs and bolts ..

 

[nickypaliwal]

DO we need any external coating such as ENP (Electroless Nickel Plated) or PTFE or any other coating in CS Nuts and Bolts to avoid dis-similar metal contact ?

Vendor proposes that they use CS studs and Bolts due to high tensile strength..

Also skid package vendor is offering CS studs and bolts for chemical injection package with all piping and equipment of SS316

 

[desertfox]

Hi nickypaliwal

If there is any electrolyte which comes into contact with both the carbon and stainless steel you will get corrosion.
There is no point in having high tensile steel bolting because if you tighten the bolts close to their yield value, you will probably find you have embedded the nuts/ washers into the stainless steel fitting as the yield strength of stainless is less than that of carbon steel.

 

[CoryPad]

Yes you should consider coating the fasteners.

 

[nickypaliwal]

Hi deserfox,

I have been thinking the same but it is not a single vendor and not a single equipment but i have been experiencing the same situation(CS studs and bolts for SS body for valves, fittings etc).

If coating is to be provided then which type? What coating is required?

 

[desertfox]

hi nickypali

you can hot dip galvanise or zinc plate,chrome plate the fasteners,chrome plate see this site:-

https://www.boltdepot.com/fastener-information/materials-and-grades/materials.aspx

My reference to the strength of the bolts and stainless was in response to your comment that, vendors had stated to use carbon steel fasteners because of the high tensile strength, well there is no point if your limited by the strength of stainless.

 

[SJones]

If your client is the usual one, then DEP 30.48.00.32-Gen would be worth a look.

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/pub/8/83b/b04

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

 

[CoryPad]

For this application, I would not use a metallic plating on the fasteners. Zinc phosphate plus organic topcoat (e.g. Xylan) is an option.

 

[Duwe6]

Rule #1 -- the Customer is always right
Rule #2 -- when the Customer demands something strange in writing, refer to Rule #1.

Unless there are significant temperature swings during operation, I have gotten good service using B7 c/s studs on S/S flange pairs. And it still looks 'wrong' to me; but it works.