Stainless Process Tubing

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jap said:
Not that I care one way or the other but my issue would be more with the welded joints than stainless vs. mild steel for the simple reason that most stainless lengths of tubing are 10 or 20' long. if you weld the joint together, unless you run a camera inside the tubing to see how the weld turned out.... which I doubt they do..... I don't see how you'd ever really know how smooth the weld turned out on the inside. :)

JAP>
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You inspect them by cutting out a random sample of finished welds and inspecting them. I saw this done in an elevator tower, and they were welds like I will never be able to make. A beauty to behold, and bent completely backwards, cut and polished, and not a flaw to be seen.
 
We've run a lot of rigid in processing plants but it was stainless rigid with stainless fittings, straps etc..... Never run any electrical wiring in stainless tubing like they use for the processing side, although it probably would be a better raceway, just seems that would be odd for some reason.

JAP>
 
iwire said:
The welding of stainless steel process tubing is a lot different than the welding done at the local muffler shop. I highly doubt it leaves anything inside the tube. It is done by highly trained TIG welders and generally has a high level of quality control.
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i've been around a lot of process piping in the food packing industry,
and i'd have zero concern about roughness inside a SS pipe tig'd.

and i've seen UL approved manufactured equipment with SS tube
used as conduit between cabinets welded. field fabrication would be another
thing... that dog won't hunt well, i suspect. you'd have to talk with
your inspector, and explain what you wanted to do, and why. YMMV.

most industrial installs, the inspector comes out, and doesn't dive into
controls and unit piping all that much.
 
petersonra said:
the place I used to work had a pipe welding machine for welding SS pipe for use in pharmaceutical and other applications where the inside and the outside of the pipe had to be perfectly smooth. The thing made very, very smooth welds. Did not require polishing afterwards, either inside or outside.
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That was probably an orbital welder. I used to work in the semiconductor industry, and for process gas piping, you didn't use anything else. Here's a catalog cut for the weld head used for 1/8" to 6" process tubing. Traveling heads for up to 64" pipe are available from some manufacturers.
 
iwire said:
The welding of stainless steel process tubing is a lot different than the welding done at the local muffler shop. I highly doubt it leaves anything inside the tube. It is done by highly trained TIG welders and generally has a high level of quality control.
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And it has to be that way to pass sanitary inspections for the product that will be pumped through the piping. Having rough edges, cracks, crevices leaves a place for product to hang up in the pipe and a place for bacterial growth to happen. Some places are not as particular with the details as others, but still have a similar goal of having a smooth finish on the interior side. Making the outside pretty is impressive to anyone looking at it from outside but the inside is the most critical to product safety.

A good installer does check his work, they use things like mirrors fiber optics, or other inspection devices that can be inserted into the pipe to get a look at their work.

I have tried to weld such piping before but was not even close to being acceptable for sanitary purposes, mostly tried to apply knowledge gained watching others as well as some how to videos found on line. But I don't consider myself a good welder in the first place and probably need much more practice before I would be all that good at something like this. Plus I don't have as steady of a hand as I used to or the patience to take the necessary time to get it done correctly. Knowing what needs to be done isn't the hard part, physically doing it takes practice to be good.
 
gadfly56 said:
It kinda backs up what I'm saying. The steel they tested was standard mild or low alloy steel, not a single mention of stainless. All those distances in the second table would have to be divided by 4. The top distance in those tables is about 400 feet, so you'd be reduced to 100 feet max, all other things being equal.
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So roughly reduced to the same level as a wire type EGC.

I guess I am not seeing the issue. :)



However the OP has not told us if these are line voltage conductors and if they are line voltage has an EGC been run.
 
McMaster Carr sells SS EMT sized conduit which I used on a project and it worked well. Sanitary stainless welds have no sharp edges inside, the lines are purged with argon
during the weld so there is no spattering. I don't know about the legality of using it for conduit but structurally it would be as good or better than rigid. I have seen it used
many times for open ended cable chases. Only issue I might see is to make sure to pull an EGC due to conductivity concerns as noted by others. But we all pull an ECG anyhow
I hope.
 
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