Material for basering and anchor chair

[jtseng123]

Dear all,
We have a short skirt 5' long so we make it all stainless steel for a SS vessel. Is there any concern of contamination for CS base ring/anchor chairs that are fillet welded to the SS skirt since they are in contact ?

If we make basering/anchor chairs to SS, is there any concern of galvanic corrosion due to galvanized anchor bolts specified by structure group for the concrete foundation ?

What do you normally do on your own design ?

 

[fegenbush]

I would have no reservations with welding a carbon steel base ring and anchor chair to the stainless steel skirt so long as the weld was made with appropriate filler and the carbon steel and weld were properly coated. Your client may think differently of this detail.

There is known glavanic corrosion issues between stainless steel and galvanized carbon steel. It is possible this will cause problems. Solutions to this problem are to either make the anchor bolts from stainless steel or install electrical isolation kits between the anchor bolts and chairs.

 

[jtseng123]

Disimilar weld is not the concern. My concern is the direct contact of SS skirt to CS basering/gussets/top ring since it is not full penetration weld. For a 20 years service life, will this direct contact weaken the strength such that I shall split the skirt into two sections, SS top/ CS bottom even it is very short ?

 

[NBrink]

Is there a large temperature swing or something that's got you concerned about the joint? Just the two being in contact on a properly designed joint shouldn't be a problem.

 

[r6155]

When I design S.S. pressure vessel all external structural and attachments are S.S. too.
Anchor bolts, and nuts, are S.S. (no corrosion allowance is added). The cost is minimum, instead of carbon steel, and zero future problems.
Regards
r6155