Mating SS Flange to CS Flange

[cheongcm]

Does anyone has any experience and/or advice with regard to corrosion aspect of mating stainless steel pipe flange to carbon steel flange? Will there be any galvanic corrosion? What materails to be used for bolts and nuts?

 

[SJones]

Depends on the fluid on the inside and the environment on the outside. For conductive, corrosive fluids, suitable insulation may need to be incorporated and/or a corrosion allowance provided on the carbon steel in and around the joint. For atmospheric exposure, carbon/low alloy steel bolting is a viable, albeit visually ugly, option (don't galvanise the bolts if liquid metal embrittlement scenarios cannot be tolerated).

Steve Jones
Materials & Corrosion Engineer

http://www.pdo.co.om/pdo/

 

[cheongcm]

Thanks SJones. Will flourocarbon coating to CS bolt/nuts of any good?

 

[unclesyd]

Coating of CS Fasteners is quite common along the Gulf Coast and getting more play in quite number of chemical companies. A lot of companies have standardized on Green or Blue Coatings for all CS fasteners above 1" temperatures permitting.
One problem we and others have run into is with CS/SS flanges in Class 150 especially in the 3" and 8" sizes.

We got into a big trap on several large projects where they used CS backup flanges for SS lines mating with SS flanges.
Just because it works on paper doesn't mean it works in the field, check around and see if your people have any experience in using the combination in certain areas as atmospherics are not the only problem as process can enter the picture.

 

[11echo]

When I run across this situation, I normally use insulating flange kits. This might not work well in wet climates or offshore setting, but here in central Calif. it works very well. ...Mark