Letter 19760

Weld Corrosion of 316L Marine Grade Stainless in Salt Water  

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I am working with 316L stainless steel to build my own ornamental fence around my beachfront property. I have been arc-welding stainless steel 316L, and have been having problems with corrosion of the welds. I have tried annealing. I have tried shot-blasting the welds. I have tried a passivation and pickling solution. The results to date have been mediocre ... I still get rust on the welds, particularly in the crevices between the two joined pieces. Now I am not certain a coating would work. It probably would not get into the crannies between the welded pieces. Also I am afraid that any paint veneer will start to peel, creating a crevice in which corrosion will form. Any ideas?

Thanks for your feedback.

Stephen Law Ryan
Homeowner. - Singapore

Hi Stephen,

This has sure come up before on finishing.com and you sure seem to have the proper things, much more so than most people do.... and you were using the L grade of 3l6.

If nothing works, may I suggest you don't use a stainless weld rod at all .... but just nickel, ie. overweld.

3l6 ss contains 4 main ingredients, Cr, Ni, Mo and Fe ... and these all have DIFFERENT melting points.

So if you weld it, use as low a weld heat as possible ... but even so, some ingredients, notably Mo, will 'evaporate' and metallurgists will talk of carbides forming (which doesn't quite make sense to me) but the ss structure at the welds will perforce change. I have heard of Argon, ie. inert gas welding of stainless, but doubt that that would be eradicate the problem because that just occludes oxygen and wouldn't contribute to a low welding temperature, I think.Go and ask a s.s. expert, OK?

Food for thought, anyhow. Let me have your thoughts, please.

Freeman Newton
- White Rock, B.C. Canada .... plastics, chemical plant, background

Dear Mr. Newton,

This is EXACTLY the kind of response I wanted ... thoughtful, intelligent, one that really addressed my problem.

Don't know if you are ever out this way, but if so give me a call for some real Asian hospitality.

Thanks again.

Stephen Law Ryan
- Singapore

Hi Stephen ! Well, I'm flabbergasted. Someone who actually had the courtesy to reply. Sure makes it worth while to try to answer some of the questions which come up. Thanks for the invite but I was already in Singapore a few years ago. Ultra clean city. Looked purposefully for debris and could only find ONE cigarette package under a bush. The tour guide was the best, highly informative lady ... far better than the Hong Kong guy. We were impressed with your bird zoo park. Very impressed. Wished sometimes we had your corporal punishment laws for certain motorists, ie. 12 year old kids who steal cars. That would sure CURE them. Have a look at # 7099 and # 12044. They might interest you. Freeman Newton - White Rock, B.C. Canada ... overlooking the Pacific ocean ... & the USA

Well, thanks a lot again. 'Glad you like my city. We say that we have a fine city, because we FINE people for dropping litter or cigarette butts on the street. We even fine them for not flushing a public loo (that may seem extreme, but it makes some sense if you have ever been to a public loo and been greeted by the residue/deposit of the previous tenant).

As for corporal punishment, we caned an American kid named Michael Fay some years back. He and his gang had spray painted 18 cars during the course of a night of vandalism. Seems that did not make us too popular ... even Bill Clinton weighed into the fight with a plea for clemency (hey, don't worry, I wanted to reassure Bill ... we are caning the kid for vandalism, not acting out perversions with a cigar). In any case, I saw the other two letters. I having been using a mild citric acid solution to pickle/passivate the welds. Do you want me to use a full-strength HCL solution instead? Or do you want me to go a get a dog?

Thanks again, buddy.

Stephen Law Ryan
- Singapore

I have been toying with the idea of just painting the welds. The only question I have is whether this won't do more harm than good. If the paint starts to scab or flake, won't it just create a cosy little cranny in which crevice corrosion will form? Anybody out there have any thoughts? Anybody out there ever try a paint product on Stainless Steel 316L Marine Grade that truly worked? Hey, thanks for the help!

Stephen Law Ryan
- Singapore

Stephen,

Re paint, not a bad idea ... but only use a Tremclad, I think (that's if you know that trade name)which might be well better than some other 'silver' paints.

Re that Michael Fay twit, he sure deserved what he got! And I believe he wasn't caned all that much ... you sure got the world's attention! A lot of hype ... in my time we always got caned for misdemeanours. This was the appropriate punishment in Public Schools (UK type). Seeing that you appreciate dawgs, sorry, dogs ... maybe there are some other sites of interest to you, maybe! Try 8367, 11868, 17085 and 17205 for a few minutes of humour.

Lastly, the next time you build a fence, use PVC ... there are some real smooth PVC fittings (made by George Fischer) versus the standard ones. Tremendous choice of colours ... white, grey, white, grey, white or even grey!

Freeman Newton
- White Rock, B.C. Canada

Hey, thanks a million ... again!

I found the address for Tremclad:
TREMCO CANADA DIVISION, RPM CANADA ADDRESS : 220 Wicksteed Avenue, Toronto Ontario
Canada M4H 1G7 EMERGENCY TELEPHONE NO. : 613-996-6666

From what I saw on a few chatlines, Tremclad appears to be a combined primer and topcoat (no priming necessary .... just spray on a few fine layers).

I don't think Tremclad is sold out here, though. Can you tell me what properties it has (i.e., what makes it so good) ... perhaps I can find something similar.

Thanks for the words of support regarding Michael Faye. You are right that we took a heck of a lot of flack on that one. But there is a difference between an essentially good kid who made a small mistake and someone with a bad streak in him. Ole Michael Faye was just plain bad to the bone. I used to have a German Shepherd of my own. Good dog, always trying to do right. Come to think of it, he was much better behaved than Michael Faye!

Thanks again!

Steve

Stephen Law Ryan
- Singapore

Dear Stephen,

If you have already welded the whole thing out then there is not much you can do at the moment. But if you ever have to do this in the future try TIG welding small portions at a time and then cooling immediately with some sort of oil. I have used WD-40 in the past with acceptable results. But there may be something better. I have experience minor rusting and discoloration of stainless in the past of all types. There is another condition which contributes to the corrosion problem and that is called chromium fallout. This occurs, if my memory serves me correctly, between 800 and 2000 degrees farenheit. TIG welding will concentrate the heat into a smaller area and reduce the heat affect zone and if your joints are tight enough make the weld faster and reduce the heat affect zone over stick welding. Also this will eliminate any grinding cleanup and there can be no reaction with the flux and the metal since it does not exist. Molybdenum may contribute to the corrosion resistance of stainless but my understanding is that the main ingredient is chromium. This also gives the silver color. Same thing as chrome on a bumper. There is oxidation that takes place but it is very slow and very hard. That is why stainless takes so long to corrode. But it will eventually corrode even if never heated after manufacture. If it is required that everything oxidize at the same rate the simplest solution would be to develop a good mechanical method of attachment. Of course this would require stainless brackets and hardware. The bottom line is that no metal can be heated and not change the basic grain structure of the metal or it elemental composition. And the critical temperature is different for each alloy. Of course welding of any kind exceeds those critical temperatures. If you would like more information on the subject and some photos of weld affected grain structure then you should contact the American Welding Society. I'm not sure of address, phone, or web site but they should not be to hard to find.

Paul McCord
- Mableton, GA, USA

Thanks, Paul. That was a very thoughtful and helpful reply. I see that you have been doing your annealing with WD40. I was planning to use water, but that sounds like a good idea.

You have a great day ... you certainly deserve it!

Take care,

Stephen Law Ryan
- Singapore, Republic of Singapore

If your fence is in the water for any period of time, it may be that it forms a voltaic cell much like a battery hence the extra corrosion.

I have heard of this occurring in yachting marinas where boats continuously moored and attached to the same jetty exhibit accelerated corrosion. Some sites exist on the web covering this phenomenon.

Oliver Williams
- London

Thanks, Oliver. It was very nice of you to write. This is another issue which I will immediately check out. Thanks again. You have a great day.

Don't forget to contact me if you are ever in this part of the world.

Stephen Law Ryan
- Singapore

Hi Stephen.

I don't know if you're still having problems with your fence but me and a friend here at the University of British Columbia think your problem with corroding 316L is very interesting.

316L is not subject to sensitization (carbide formation in the heat affected zone)and has ok chloride corrosion resistance at room temperature but it is very sensitive to chloride corrosion at high temperatures (~60 C).

You may be losing your alloying elements at the weld site to oxidation (Chromium and Molybdenum) so you can try welding at the lowest temperature possible.

Feel free to quench your weld too, 316L is stable in its austenitic phase and shouldn't go brittle. Quenching it in water with baking soda in it will help prevent pitting corrosion. Leave it in a baking soda solution for 5 minutes or so.

It's got everything to do with that damn seawater and perhaps heat (is there any chance your fence is getting really hot?).

You could always use aluminum if you really want, but it's no fun to weld.

-cheers

Cameron Rout
- Vancouver, BC, Canada

Hello. Please allow me to preface my comments with a bit of background information. I work for a manufacturer of extremely high quality condensing boilers and water storage tanks. We use 316 ss tiantium based material. We have some storage tanks installed in a marine fish hatchery. Boilers raise the salt water inside the tanks by a few degrees to accellerate the germination of Salmon eggs. These tanks have been in service for approximately twelve years without signs of corrosion.

All of our SS products are manufactured in facilities that have no ferrous metals near them. Our SS fabricators do not work with ferrous metals. The hand and power tools that are used in the facility have never been used with other metals. If you detect a corporate paranoia concerning the possibility of cross contamination between teh SS and other materials then I have communicated correctly.

We allow the cleaning of our products only with non-chlorinated cleaners. Do NOT use HCl. Do NOT use a wire brush. Do NOT use grinding or polishing wheels that hacve been used previously. Do NOT use a filler rod when welding. Use ONLY TIG or fusion methods to weld 316. Protective (shielding) gasses must enclose all surfaces of the welded material, inside as well as the outside of the tubing.

There is only one product that can adequately passivate 316 ti SS and that is made in Switzerland. In Canada the product is called Antox 75E.

The rusting that you are experiencing is not stoppable with barrier methods such as paint. Please do not apply aluminum based paints to 316SS either. Not only are you waisting your money but Aluminum is not too well matched to SS electrically.

Thanks for posting an interesting question.

Fred Meiewr
- Chilliwack, BC, Canada

One main problem that you may have is cross contamination from carbon steel to stainless.
Most shops in our area including ours segregate stainless fabrication from carbon steel.
In other words when you are fabricating any stainless steel you need to keep it away from any carbon steel product otherwise the stainless weldment will bleed rust if it came in contact with a carbon steel product.
That applies to using stands and or carbon tables to weld on while preparing your stainless weldment.
A real true stainless shop will have stainless tables and stands to fabricate with.

Peter Hayes
- Beaumont, Texas, USA

In the kitchen equipment fabrication industry we electroplated all Stainless Steel TIG welds with a portable plating unit. It is just like the ones the gold platers use in the car business. It was required for USF approval. We made freezers, refrigerated cabinets, serving tables, waitress stations etc. The welds do not corrode in any case.

I believe all you are really doing is vaporizing out all the nickel in the weld joint when you weld it, and the plater adds enough back to keep it corrosion free, if done properly.

I think that may have been referenced above in another response.

Hope the memory helps.

Google ss weld plater and see what comes up.

It just gets better and better :-)
(Say that 3 times without smiling)

Larry Howle
- Columbia, SC, USA

I don't know if you are still dealing with that fence...You could try welding the whole thing with Monel 67 tig wire. Just run it over the existing welds after cleaning them up.

Red Brown
- Appleton, Wisconsin, USA

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