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Corrosion on CSST?


Jim Katen
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I saw something disturbing yesterday. It was condo that was constructed on the Oregon coast, just a few feet from the beach, in 2005. The gas furnace is in the attic. Just above the furnace, the CSST that feeds the furnace had a small spot of rust right on the stainless steel, right on the lateral seam. Gas was leaking from the rust spot.

Has anyone heard of CSST rusting or corroding? It looked like, if I were to flick at this bit of rust with my fingernail, I'd have a sizable little hole in the pipe. I took the liberty of shutting gas to this unit.

Here are some pictures. They're the best that I was able to get. The attic was hot & small and my face was pressed against the hot B-vent. I snapped a half dozen pics, but none came out well.

Download Attachment: icon_photo.gif CSST (1).JPG

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Download Attachment: icon_photo.gif CSST (2).JPG

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I'm not sure what grade of stainless CSST is... to be resistant to corrosive atmospheres it should be 316. I bet it's 304.

That said, the issue in the photo looks like a manufacturing defect where an imperfection or some sort of contaminant was fused into the seam weld.

I had the same thought. It looks like a bit of debris got caught up in the seam. I suppose that their QC program can't catch everything.

I doubt that it's metal fatigue. CSST can take an amazing amount of manhandling before fatigue sets in. Even then, it usually results in cracks, not holes. And I doubt that it's lightning. We just don't get much up here - especially at the coast.

Here's a picture of it before I dribbled gunk on it and wiped it off.

Download Attachment: icon_photo.gif IMG_7724.JPG

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JK - Here's hoping that the CSST had enough clearance from the roof decking and shingle nails as well.

See so much of the "lack of clearance" issue down here.

Thanks for the information on this find ... haven't seen that one "yet".

I remember that. A whole subdivision with the CSST pressed up tight against the underside of the roof deck.

I've never seen that done here.

- Jim Katen, Oregon

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Ramon has got it. The alloy has impurities in it that cannot tolerate the corrosive coastal environment. It would be interesting to see that entire length with the jacket removed to see just how many blemishes there are. As good as he is, I wouldn't think that Jim found the only one. That's scary.

Tom

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Go here and look at the post made at 9:35 pm on October 11

http://www.heatinghelp.com/forum-thread ... -Ward-Flex

Interesting. But not relavent to this particular house. No copper pipe or flux in the place.

No mouse pee either. Where there's mouse pee, there's mouse poop. And I didn't see any mouse poop anywhere in this place.

- Jim Katen, Oregon

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  • 4 years later...

If that's Gastite it's not installed correctly. The jacket should run all the way into the fitting with Gastite. Other CSST fittings don't have this feature. The hole is probably caused by chloride pitting corrosion to which stainless is vulnerable. Chloride is in sea salt, as in NaCl, sodium chloride, or table salt. If chlorides are present, either don't use CSST, use Gastite correctly, or wrap the ends in F4 tape.

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If that's Gastite it's not installed correctly. The jacket should run all the way into the fitting with Gastite. Other CSST fittings don't have this feature. The hole is probably caused by chloride pitting corrosion to which stainless is vulnerable. Chloride is in sea salt, as in NaCl, sodium chloride, or table salt. If chlorides are present, either don't use CSST, use Gastite correctly, or wrap the ends in F4 tape.

Good observations. But there was plain old steel all over the place in this attic and none of it was corroding. If there was an environmental explanation, like corrosion from chloride, why was the plain non-stainless steel in the attic not showing the least sign of rust or decay? Nail heads, nail tips, Simpson fasteners, truss gang plates, furnace jacket - all corrosion free.

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Jim, the first photo is pretty good. The rust spot is right at the weld seam. It looks like there is pitting in around much of the same corrugation. I'd suggest sending that photo to the manufacturer. Maybe they will have input. If not, they should see this.

Do you think a lightening strike could have caused the hole and the corrosion is the result of impurities in the gas?

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Jim, the first photo is pretty good. The rust spot is right at the weld seam. It looks like there is pitting in around much of the same corrugation. I'd suggest sending that photo to the manufacturer. Maybe they will have input. If not, they should see this.

Do you think a lightening strike could have caused the hole and the corrosion is the result of impurities in the gas?

It was 5 years ago.

I doubt that it was from a lightning strike. If it was a direct strike, then the whole thing would have blown up. If it was a nearby strike, then wouldn't there have to be something nearby for the CSST to arc to? There was nothing particularly close to this for it to arc to.

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I know that if too much heat is applied to stainless steel during welding or fab process carbon is created/added to the material,that will cause rust to form in the material.

Im not sure if that's what is causing this problem though.

Either way I think csst/trac pipe is really nasty/sloppy looking stuff no matter how its installed.

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I know that if too much heat is applied to stainless steel during welding or fab process carbon is created/added to the material,that will cause rust to form in the material.

Im not sure if that's what is causing this problem though.

Either way I think csst/trac pipe is really nasty/sloppy looking stuff no matter how its installed.

Carbon is not "created" during welding or fabrication. Chromium carbides can precipitate under certain circumstances during fabrication which depletes the surrounding area of corrosion resistant Chromium oxides.

The corrosion that Jim found is probably the result of an inclusion in the base material at that point or, more likely, a contaminate in the filler material used during welding. These things happen during manufacturing. These things happen much more frequently with Chinese manufacturers.

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