Stainless Fastener Corrosion

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Just curious on your opinions on the cause of this. Customer print called out for STEEL brackets with 18-8 stainless steel nuts welded to it for stainless bolts. Bracket was immersed in lake water for several months and the stainless fasteners rusted together and seized up. Customer is now asking me what's the best way to fix this problem for future brackets. Is this a cause of cross contamination from the steel bracket, or would 316 stainless fix this? Also considering offering galvanized fasteners as an alternative.John 3:16(2) Miller Pheonix 456(2) Millermertic 252Dynasty 210DXHobart 210MVPDoringer D350 SA Cold SawScotchman 350LT Cold SawWebb 10x50 MillWebb 15x40 LatheGeka Bendicrop Ironworker
Reply:Could be a few things. First, 18-8 is about like 304 stainless. It's not as corrosion resistant as 316. Second, welding stainless, as you did with the nuts, can decrease its corrosion resistance because of carbide precipitation. (You also alloyed the SS with the mild steel, which will reduce corrosion resistance.) You really want to get in and get out in a hurry when welding stainless. The less time it spends at elevated temperature, the less its corrosion resistance will suffer.Third, you probably have galvanic corrosion happening. You can reduce this by putting something in the threaded connection (like Permatex Aviation Gasket Sealer, or anything like that) to try to keep water and air out, but you can't eliminate it reliably, at least not in saltwater.I'd go to 316, would weld it only if absolutely necessary, and get it done in a hurry if I did, and seal up those threads with some gasket gook. (You also might consider brazing it, but copper alloys are so noble that generally they accelerate galvanic corrosion, and the SS is what will suffer in that combination.)Good luck.Last edited by Kelvin; 12-22-2014 at 09:57 AM.
Reply:Offshore apps, we use 316SS with Aqualube on equipment. Galvanic corrosion is a beeyotch in the salted sea and requires sacrificial anodes or impressed current systems.  SS against mild steel equals No Dice."Discovery is to see what everybody else has seen, and to think what nobody else has thought" - Albert Szent-Gyorgyi
Reply:The one they have done now is a prototype. So they just want to improve future designs. I know 316ss is more corrosion resistant, but I thought it was only better in the case of acid or salt water? Wouldn't it still corrode just as bad as the current setup? I have several hundred 304 nuts and bolts for this application so I'd really like to stick with this design, but definitely don't want future rusting. I think first I'll recommend using an anti-seize or thread lube for their next test run, and then explore possible material alternatives in the future if it still is corroding. Any paticular recommendations on what anti-seize to recommend? Aqualube and anything else?John 3:16(2) Miller Pheonix 456(2) Millermertic 252Dynasty 210DXHobart 210MVPDoringer D350 SA Cold SawScotchman 350LT Cold SawWebb 10x50 MillWebb 15x40 LatheGeka Bendicrop Ironworker
Reply:@ Econdron - Aqualube or MoS2 (moly disulfide) may aid in corrosion resistance."Discovery is to see what everybody else has seen, and to think what nobody else has thought" - Albert Szent-Gyorgyi
Reply:I always use never sieze on the threads
Reply:I'm not familiar with Aqualube, but most anti-seize compounds contain various metals ... moly, nickel, even copper. In an electrolyte (any water except distilled water), these dissimilar metals are probably going to cause galvanic corrosion. Aqualube sounds like it was was probably made for what you're doing but if you don't have that, I would use some kind of gasket cement or even Loctite rather than anti-seize. The reason they work is because they fill the space between the threads, excluding water and oxygen. Most anti-seizes will fill that space with a mixture of grease and powdered metal of some kind that could make the corrosion worse if submerged. Outboard engine manufacturers recommend gasket sealer, not anti-seize, on their fasteners.I also think the alloying of the SS with the mild steel when you weld them together is going to give you fits.Galvanized fasteners might buy you some time, but eventually, the zinc coating is going to disappear (on boats, zincs are called "sacrificial anodes" because they "dissolve") and you'll get rust. Rust never sleeps.Last edited by Kelvin; 12-22-2014 at 05:14 PM.
Reply:Much better than antisieze... This stuff works wonders.http://www.boatoutfitters.com/tef-ge...FbBm7AodxRcA8wMiller Big 40GMiller HF-251 D High FreqVictor OA Lincoln 135 MigMK 3A CobramaticBridgeport J HeadCronatron OxylanceRadnor ACAG TorchWeldcraft TIG Torches1 blown knee and two 5 Gallon pails away from being a hero.
Reply:Here's a short informative article on thread galling that might be useful.   As one possible solution to galling on stainless it says you shouldn't use the same grade of stainless for both the nut and bolt.   A better idea would be to pair a 304 bolt with a 316 nut (or vice versa).http://www.estainlesssteel.com/gallingofstainless.html
Reply:Braze brass nuts to the steel and use stainless bolts.Mike
Reply:Originally Posted by Cape Cod GaryMuch better than antisieze... This stuff works wonders.http://www.boatoutfitters.com/tef-ge...FbBm7AodxRcA8w
Reply:Duralac (UK) also produces a "Green" enviro version.  The literature says sans Chromate compounds (safer) with increased resistance over the standard Duralac.  Never tried either version."Discovery is to see what everybody else has seen, and to think what nobody else has thought" - Albert Szent-Gyorgyi
Reply:After you weld a nut you really should chase the threads. Use all 316 hardware and it should be fine.Welding/Fab Pics: www.UtahWeld.com
Reply:I think leightrepairs has the best overall solution. The brass nuts holding my aluminum outdrive on don't corrode to the stainless studs at all in salt water. And you avoid all that precipitation stuff trying to weld on stainless that will be immersed.
Reply:You said "lake" so I am assuming completely fresh water.  Brackish or saltwater change 304L to 316L.  Change the brackets to 304L stainless. use 304L fasteners and 304L filler.  DONT over heat the stainless too much, get in and get out.  If you don't all this you are going to get some corrosion in the HAZ.  Are you sure you really have 18-8 stainless fasteners?  A lot of times you don't get what you ask for (seen this many times).
Reply:I would play around with scrap and fasteners, as some have suggested, dunk them in lake water for a week or two, and pull them out.  It may be that the bolts will seize immediately, even without water, and that the water has little to do with it, especially if you use high torque on the bolts.Given that you are in fresh water, I am inclined to think that anti-seize is the key, rather than galvanic corrosion.   The suggestion of 304 nuts and 316 bolts might also work; I understand that if the two parts are of the same alloy they are much more likely to seize.Sculptures in copper and other metalshttp://www.fergusonsculpture.comSyncrowave 200 Millermatic 211Readywelder spoolgunHypertherm 600 plasma cutterThermal Arc GMS300 Victor OA torchHomemade Blacksmith propane forge
Reply:Originally Posted by atgThe brass nuts holding my aluminum outdrive on don't corrode to the stainless studs at all in salt water.
Reply:Originally Posted by KelvinCould be a few things. First, 18-8 is about like 304 stainless. It's not as corrosion resistant as 316. Second, welding stainless, as you did with the nuts, can decrease its corrosion resistance because of carbide precipitation. (You also alloyed the SS with the mild steel, which will reduce corrosion resistance.) You really want to get in and get out in a hurry when welding stainless. The less time it spends at elevated temperature, the less its corrosion resistance will suffer.Third, you probably have galvanic corrosion happening. You can reduce this by putting something in the threaded connection (like Permatex Aviation Gasket Sealer, or anything like that) to try to keep water and air out, but you can't eliminate it reliably, at least not in saltwater.I'd go to 316, would weld it only if absolutely necessary, and get it done in a hurry if I did, and seal up those threads with some gasket gook. (You also might consider brazing it, but copper alloys are so noble that generally they accelerate galvanic corrosion, and the SS is what will suffer in that combination.)Good luck.