Using SS bolts on CS 1

[AA Abdullah]

The CS vessel i am designing has an SS stack on it. There are two flanges joining the stack to the vessel, one flange is CS (attached to vessel) and the other is SS (attached to stack). Now I am confused that at this junction which bolt material should I choose; CS or SS?

 

[XL83NL]

Typically CS, but the correct answer is difficult to give as a lot of details are missing. What service conditions do you have for example?

Huub
- You never get what you expect, you only get what you inspect.

 

[Christine74]

I'd first point out that all of the Code bolting materials that I'm familiar with (SA-193, SA-320, etc.) used for pressure equipment are actually considered to be low alloy materials, not carbon steel.

I don't know the specifics of your particular application but my experience has been that low alloy bolts are routinely used with stainless equipment provided that the bolts are not exposed to the fluid being processed/stored.


-Christine

 

[AA Abdullah]

The vessel service is Caustic, temp is 100C and pressure is 150 psig. So far taking ASME VIII Div I UG 44 into consideration I have decided to use SA 193 B8 CL2 bolt material which is SS. Although, I do wonder, doesn't CS material cause contamination in SS material? I mean when we manufacture the materials we make sure that SS equipment are kept separate from CS to avoid any kind of contamination, won't that be an issue here?

 

[AA Abdullah]

or as per @Christine bolt materials are low alloys and not CS so there is no chance for contamination regardless of using SA 192 B7 or SA 193 B8 Cl2

 

[Dhurjati Sen]

Make everything CS, including stack and flange (which you intend to make SS).

Go for internal painting at the stack location to prevent dew point corrosion.

Else, you would be inviting galvanic corrosion of the CS.

DHURJATI SEN
Kolkata, India

 

[SJones]

What is the atmospheric classification of the site? If it is C5, or CX, maybe avoid B8. B7 with suitable corrosion protection will suffice. Note: suitable protection is one that either will provide cathodic protection or one that will not suffer degradation that exposes small areas.

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/in/drstevejones

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

 

[r6155]

Some data: shell and stack diameter, height of stack, wind, seismic....?

Regards.

 

[Krausen]

I would go with CS bolts (SA193-B7s) still. They will be cheaper than SA193-B8Cl2s & will match all your other vessel studs. They also will perform better from a stud relaxation standpoint (if that becomes as issue). And you won't have to worry about the potential of galling SS bolt threads

 

[mk3223]

Q: How the Caustic vessel connected to the SS stack (vent to ATM?) under the 150psig pressure? And, it's helpful if a picture can be shared?

IMO, the bolting on the flange (CS to SS material) is acceptable in the dry ATM environment. it may consider to have a protective coating if it's in the wet and coast environments.

 

[georgeverghese]

Use an insulating pipe flange joint arrangement - commonly used for these applications to avoid galvanic corrosion. Speak to a piping engineer if not familiar.

 

[PersonalProfile]

I am not familiar with the application etc, though the following may be of interest in principle:

Carbon steel bolts in stainless steel members should be avoided because the ratio of the area of the stainless steel to the carbon steel is large and the bolts will be subject to aggressive attack.

https://www.newsteelconstruction.com/wp/ad-339-stainless-steel-in-contact-with-other-metals/

 

[r6155]

An alternative is to use both CS flanges.

Regards

 

[myname_earl]

teflon coated CS bolting will better avoid galvanic corrosion and is the only bolting we use now

Mechanical Integrity Specialist (Year 1)

 

[r6155]

Search in internet "Flange Isolation Kit for Cathodic Protection".

Regards

 

[Muhaka22]

B7 material is usually sufficient