Landracing Forum
Tech Information => Technical Discussion => Topic started by: Jonny Hotnuts on February 27, 2011, 12:38:26 PM
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Just recived a bunch of free 18g stainless plate. There is a bunch of stuff I am needing to build but was wondering how SS holds up to the salt.
please no "Robert Steel" jokes.....
~JH
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Just recived a bunch of free 18g stainless plate. There is a bunch of stuff I am needing to build but was wondering how SS holds up to the salt.
please no "Robert Steel" jokes.....~JH
I'm sure that part is for you Bob....
What type SS, some of them are less stainless than others.... and if you leave salt on them long enough you will see some reaction.
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JHN,
Stainless is affected by the salt but much less than normal steel or aluminum. I am attaching a pic of a car being built by the Fergusons that has a stainless frame. This car was originally started by Ermie Immerso (spelling ???)and is powered by two PW gas turbines. No problem here with rust on the frame.
Rex
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How much stainless is affected by salt depends on the type of stainless. 304 will be affected more than 316L. However I was maintenance manager in a pickle factory and we pitted 316L stainless but now where as much as plain carbon steel.
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I just picked up another order and found out that it is in fact 304, but its quite a lot of material (with the second order totals about 400 pounds 18g sheet), it was free and I sure aint gonna look a gift horse!
~JH
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Issues of stainless steel in a high chloride atmoshpere have filled thousands of pages of books. Some people have even devoted their entire careers to studying the problem.
In the case of 304 you face one main issue if you intend to weld it. That problem is sensitization. What happens is that during the weld process a region on the edge of the heat affected zone is raised and held in a temperature range that allows the carbon and chromium to find each other and form carbides. This depletes the region of chromium and leaves it venerable to oxidation since it no longer has the protective chromium oxide layer on the surface. If you have ever seen a weld on stainless steel that has "wagon tracks" alongside the weld that is what happened.
The bad news is that your 304 is much more susceptable than if it were 304L, a low carbon version of the same material. The good news is that not all hope is lost. You can greatly decrease the amount of sensitization by following a few simple rules.
1: Use a low carbon filler. 308L would work well for your 304.
2: Limit the amount of welding. That one is pretty obvious.
3: Use a chill bar behind the weld and even alongside if possible. Copper chill bars will cool the weld quickly and reduce the time the HAZ is in the critical temperature range.
4: Low heat input weld process. Use Mig if you can.
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I have beer at my house, and thus I pose some questions If you will Monsieur Willard....
we have a few stainless bits and pieces around the car...some of the cooling system, some of the vac-u-pan lines, and also some heat shields and covers None of it is structural or very high pressure. Like the hack that I am I just weld them up with mild wire in the mig but there is something I have noticed .
The welds don't rust.
I would have thought the welds on the cooling system pipes would be the first thing ....
what gives?
btw: I make an effort to keep the welds as cool as possible, I tend to weld like I'm butt welding thin plate,bang, bang, bang......very short pulses.
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Your "bang, bang, bang" method of welding, using short pulses, is not allowing the carbides to form. This leaves the chromium to do it's thing, which is to create a chromium oxide layer on the surface that prevents further corrosion. You didn't mention what alloy of SS you were welding on, but if it were a low carbon alloy that would contribute. Typically a mild steel Mig wire will have less than .15% carbon, most are around .07%-.09% which also would prevent some of the Cr from being depleted.
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Great info.........................thanks to all.............................................................................
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Back when i was working on communication towers we used a lot of stainless steel but the problem was never the stainless it was how things where bolted to it. We had a lot of issues with the nuts and bolts after time because of the mixing of metals and people not using never seize or plastic washers to isolate the different metals.
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Last year I put a lot of stainless fasteners on the Triumph. There were no problems with most of them when I took the bike apart this winter. The problems were with stainless bolts or screws in aluminum. The aluminum oxidized around the threads and the fasteners were very difficult to remove. The stainless did not corrode.
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Wobbly
Working on big trucks, I have seen bolts twist off before the aluminum corrosion let them turn (bigger problem then).
I started using silicone gasket maker on the bolts before installation and after chasing threads and cleaning holes, especially in blind holes. It seems the silicone seals out moisture which at least minimizes if not stops the corrosion. The silicone is soft enough to easily shear for removal and not a problem to clean. It also could act to keep bolts from vibrating out if they get loose. I use the clear and wipe the excess off after installation and it's almost invisible.
YMMV
Ron
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One big problem with using stainless bolts in aluminum is that the dissimilar metals generate galvanic corrision but even without corrosion this combination is almost guaranteed to gall, either breaking the bolt or stripping the threads out of the aluminum. :x
These problems can be prevented by using "Never-Sieze" on the threads. It is also useful for header bolts and nuts where oxidation (rust) is a problem.
Regards, Neil Tucson, AZ