Contact corrosion flange - bolting
Contact corrosion flange - bolting
(OP)
I've seen several piping-spec's where galvanised stud-bolts are used in combination with stainless steel flanges.
Therefore I would like to pose a question about contact corrosion between the galvanised bolts-nuts-washers and the stainless steel flanges. Is it not neccesary to worry about this, or are measurements needed (for instance: stainless steel stud-bolts & nuts, plastic washers, protection against electrolite (rainwater))
I also notice that some spec's describe the use of washers, and others don't. What could be an explanation and what is recommended?
Thanks,
Therefore I would like to pose a question about contact corrosion between the galvanised bolts-nuts-washers and the stainless steel flanges. Is it not neccesary to worry about this, or are measurements needed (for instance: stainless steel stud-bolts & nuts, plastic washers, protection against electrolite (rainwater))
I also notice that some spec's describe the use of washers, and others don't. What could be an explanation and what is recommended?
Thanks,





RE: Contact corrosion flange - bolting
Galvanised studbolts used with SS flanges not a good combination. Zinc will attack SS especially if within a fire and compromise the structural integrity of the flanges.
RE: Contact corrosion flange - bolting
The liquid metal embrittlement concern noted above is a little overblown in my opinion. The same spec which calls out the galvanized hardware for the flanges probably requires/permits galvanized pipe shoes etc., and for moderate temperature SS lines, personally I don't see the problem with that.
If you don't agree with that, there's always B8 stainless or fluoropolymer coated hardware as a zinc-free alternative.
RE: Contact corrosion flange - bolting
Our case many be unique as we required the highest possible utility possible since taking a process system down coast many thousands of dollars due to lost production which can't be recovered as the plant is at 100% capacity.
Adding to the galvanized fasteners we have been forced to use ductile iron backup flanges, another bad decision for our process system. Again many thousands of dollars to replace them.
I would go with B* Class 2 under 1 1/8" and B* above. We do use some Green and Blue Teflon coated B7 on SS non-process lines like pure water, process air, etc. We loose a few SS fasteners to galling, but the use of thread lubricants mitigates the problem somewhat.
RE: Contact corrosion flange - bolting
We're perfectly comfortable with galvanized pipe shoes and other galvanized support components in low to moderate-temperature services.
RE: Contact corrosion flange - bolting
The Teflon coated bolting we've used before, but they are quite expensive. (like Stainless steel) SS bolting always needs adequate greasing because of the fast "gripping". But I also think it is wise to use SS bolting on SS flanges.
In certain cases we also use galvanized pipe supports on SS pipes, but we wrap the piping to avoid contact corrosion.