SS304 Corrosion or Byproduct of Thread Lube

[sewerratt]

What is causing this and is it a cause for concern? (See pic) We have 304 stainless pipe, bolts, nuts, & washers (per submittal) submerged in a storage tank holding treated, chlorinated drinking water. pH is 7.7. Chlorine residual is 1.7ppm. Pipe was installed about 6 months ago. Tank was brought off line and drained to inspect another item and this was found. Posts elsewhere suggested a reaction to thread lube, but I found a post here about Chloride induced Stress Corrosion. Any thoughts?

thanks

 

[sewerratt]

Sorry, the picture link didnt quite make it. It should be below

 

[rconner]

Was curious have you confirmed with the installer (or inspector etc.) that "thread lube" was in fact used? If so, what was the generic type or specific brand?

 

[EdStainless]

You need to take a few of these apart and see if you have crevice corrosion. My guess is that the lube was soap based and contained chlorides. You may have a real problem.

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Plymouth Tube

 

[strider6]

one question: this pipe is in 304 L SS and is inside a tank. But what's inside this pipe? the same water?
it seems that you've a terrible welding and that some of the lube is coming out of the weld (the two small ball in the middle of the picture) and also that you've corrosion on the internal wall of tank.
Sure that this is potable water and someone drink it?

S.

http://www.corrosionist.com

 

[sewerratt]

This is an elevated finished water tank. Was blasted and coated in and out within the last year. The SS piping was added with diffusers to distribute incoming water more evenly to prevent stratification. The area in the picture is usually submerged. Finished water inside and out of the pipe. 1 Mgallon tank. See additional pics attached.

 

[sewerratt]

One more pic

 

[rconner]

This is probably a stupid question, but I guess I'll go ahead and ask it (as it was at the heart of my original questions). Why would someone use "lube" to assemble these flanged piping materials?

 

[sewerratt]

Still trying to verify this, but the lube (or loctite) may have been used on the the bolt threads to keep the SS threads from galling when tightening (or loosening after installation).

 

[CoryPad]

Yes, a thread lubricant is necessary to prevent galling.

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[EdStainless]

304 isn't always too happy in potable water. Rough welds, crevices, surface oxidation(or worse someone trying to clean it up with grinding wheels or wire brushes) can all result in poor corrosion resistance.
Nuts and bolts are mass produced crevice corrosion fixtures.

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Plymouth Tube

 

[rconner]

Thanks for the education. I was aware from many years ago that some stainless steel bolting materials, and maybe particularly of the 304 type variety, were prone to "galling" (but as I don't deal regularly with this material as piping I am embarrassed to note I was unaware, however, that "lubricants" were claimed to prevent this -- I believe at least in the past or in other applciations there have been other potential solutions to galling problems, e.g. selection of other bolting etc. alloys maybe less prone to the behavior).

 

[Compositepro]

I think thread lube is a red herring. Looking at the pictures I though that it looks very familiar but it took a while to remember where I've seen very similar deposits before. I've seen very similar deposits in old hot water heaters. These are probably mineral deposits that caused by galvanic currents. I'm only speculating about the cause but that is where I've seen this before - same shape, texture, and color.