galvanic corrosion: C937 Bronze/Stainless Steel
galvanic corrosion: C937 Bronze/Stainless Steel
(OP)
I have been asked if stainless steel bolts can be used to fasten together a two part C937 Bronze (80%Cu, 10%Pb, 10%Sn) sealing ring without risking galvanic corrosion (water (80 deg C) on one side, hydrocarbon vapour on the other side). I've tried to consult the galvanic serious but find myself confused.
Stainless steels are listed in their active and passive forms. I realize that the passive form indicates a chrome-oxide coating. Can it be assumed that a stainless screw would be passive? Do you consider a material active only when it is being eroded causing removal of the passive layer?
Does it make sense to use stainless steel fasteners for bronze material? Any advice would be helpful as my knowlege of galvanic corrosion is a bit lacking. Thank you.
Stainless steels are listed in their active and passive forms. I realize that the passive form indicates a chrome-oxide coating. Can it be assumed that a stainless screw would be passive? Do you consider a material active only when it is being eroded causing removal of the passive layer?
Does it make sense to use stainless steel fasteners for bronze material? Any advice would be helpful as my knowlege of galvanic corrosion is a bit lacking. Thank you.





RE: galvanic corrosion: C937 Bronze/Stainless Steel
Can we assume the bolts get wet? How pure is the water? Can't you find bronze bolts?
RE: galvanic corrosion: C937 Bronze/Stainless Steel
I believe the thought was to go for stainless bolts out of convenience but I can look into it and see if we can get some bronze bolts in.
How do I determine if the bolts will be active or passive? My thoughts are that if they are passive then I should be fine - bronze will be the anode and will be a lot bigger than the cathode so it shouldn't cause any problems. But, if the bolts are active (still trying to figure out what kind of stainless they want to use by the way) then I may have a tiny anode and large cathode which in my mind wouldn't be a great idea.
Thanks for the help, I look forward to hearing more.
RE: galvanic corrosion: C937 Bronze/Stainless Steel
Given your temps. and Cl level, I'd be concerned with the usual 304/316 bolts, especially when you consider the crevices. McGuire will probably jump in here, but I'd say use 2205 SS as a minimum if you can't find bronze bolts. Do NOT use common brass bolts-they will be the anodes against your bronze.
RE: galvanic corrosion: C937 Bronze/Stainless Steel
RE: galvanic corrosion: C937 Bronze/Stainless Steel
http://www.bulten-stainless.se/eng/index.htm
RE: galvanic corrosion: C937 Bronze/Stainless Steel
Thanks again.
RE: galvanic corrosion: C937 Bronze/Stainless Steel
Ken
RE: galvanic corrosion: C937 Bronze/Stainless Steel
RE: galvanic corrosion: C937 Bronze/Stainless Steel
Copper-based alloys are not really my bag...I thought I would let others comment upon suitable bronze alloys for this application.
RE: galvanic corrosion: C937 Bronze/Stainless Steel
Look at thread 124-71885 concerning Si-Br fasteners.
RE: galvanic corrosion: C937 Bronze/Stainless Steel
On a side note: Metalguy - in your first reply you mentioned that you should never assume SS bolts are passive. I'm guessing you would consider them active if corrosion or erosion is destroying the passive layer - is this correct? Are there any other times that you would assume a metal is active?
RE: galvanic corrosion: C937 Bronze/Stainless Steel
So, the bottom line is to always assume that something like bolting is active, and make sure it will readily repassivate during use. Crevices are especially bad for 304/316, because they concentrate ions, esp. Cl to far higher levels than the bulk fluid.