View Full Version : Cleaning silicone off S.S. to weld.

oddball racing
03-03-2017, 02:33 PM
Got a job to weld a rectangular stainless water reservoir tank. This tank had seen multiple overpressures resulting flexing that caused welded edge seam to fail.

Before I was called, they attempted to seal cracked seam with silicone sealant and an overcap of stainless angle that was more of less glued over the seam. I've used a 4 inch grinder and cup wire wheel to rid the tank of sealant, but still sort of feel remnants left behind. In trying to get the ultimate cleanliness before welding what should I use to clean remaining residue? Any suggestions/ tips?

Thanks brain trust, Mike

03-03-2017, 02:37 PM

I would turn this job down in a second. High pressure vessels, especially ones that have burst, are no joke. Don't attempt to repair them for a small profit which might be taken away in a liability claim or lawsuit. Be very careful and explain in writing (with customer signature, and give one copy to your customer) that you guarantee absolutely nothing and take no liability in case it ruptures again.

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03-03-2017, 02:55 PM
Liability withstanding..... try a "body solvent" that is used to prep for automotive paint.



03-03-2017, 03:03 PM
And in case you have not heard this before brake cleaner has no place around anything to do with welding. Don't even think about it. ANY residue from the usual ingredients in common brake cleaners can produce deadly phosgene gas.

Mike Burch
03-03-2017, 03:32 PM
You are right to be suspicious. Silicone diffuses into any surface it is on, and the only way to get rid of it all is to grind it out. Horrible bloody stuff - it should be avoided at all costs.

As Andre has said, flag this one away. You are proposing to do a weld repair which you cannot guarantee on a pressure vessel over whose future abuse you have no control. Let someone else carry the liability.

oddball racing
03-03-2017, 08:05 PM
Nope. Not a pressure vessel at all. Simply a reservoir. Stainless steel about 3/32 thick, whatever ga. that is. Problably 25+ years old, but looks good in and out. Recycle tank for a camel-type vacuum pump. SUPPOSED to run at atmosphere.

Over the years, low maintenance of clogged exhaust vents, it would back it up, making it flex. After it happened enough times.... well, here we are.

At work project. No liability issues here. It's all on them.

The question should have been what do I WASH it down with that would best cut the "feel" of any silicone left behind? Yes, I do know about brake clean and phosgene though, thanks.

I have already warned them of contaminated welding issues. We are going into it as an attempt to save them of replacing the tank. Just trying to increase my chances are pulling one out of the hat.

03-03-2017, 08:37 PM
the problem is not the salient. it is why does it keep cracking. sounds to me like metal fatigue. if it is you will have to replace the whole corner.

03-03-2017, 08:57 PM
Dow Corning DS2025 silicone cleaning solvent. A little pricey but it works!


oddball racing
03-04-2017, 07:45 AM
Doesn't keep cracking. It's cracked for the first time. ..and not a fatigued corner, on the original welded seam. I assume the welded seam to be the most brittle part do to the H.A.Z. Stainless doesn't anneal the same as mild steel.

03-04-2017, 09:08 AM
how about burning it off?

J Tiers
03-04-2017, 10:49 AM
how about burning it off?

Actually, YES. It should turn to an ash at several hundred degrees, although the smoke is nasty and you should stay out of the smoke. Just heat it up and it should be gone well before a dull red heat. The ash is not adherent, and will probably blow or brush away fairly easily.

Cleaning solvent works, but if the stuff is in the crack, it won;t work as well. heat will get all of it, although the ash in the crack may be harder to remove, it may float up when welded. You will grind some part of the joint to do the repair, so......

03-04-2017, 01:37 PM
And if all else fails, you can do what they (sort of) did before. Weld in a stainless angle as an overcap. Using the proper size will move your welds outside of where the silicone was applied.


03-04-2017, 01:51 PM
...but if the stuff is in the crack...

This is the real problem right here. And it's not a question of if, there will be contaminant in the crack. Smearing silicone
over the crack, especially if you use a cap of some sort that applies some pressure, will ensure that there's silicone inside.
Some concentrated heat is the best way to get rid of it...

...although the ash in the crack may be harder to remove, it may float up when welded. You will grind some part of
the joint to do the repair...

Yeah, even with a decent pre-clean there's still a good chance that you'll have to grind out some bad spots--just goes with
the territory when you're doing repairs of this nature. How are you doing the repair? Tig? Or? Tig will give you the best
result but it is a bit more sensitive to contamination than other methods...