Stainless Process Tubing

[CTuttle]

I ran into this a few times and i am wonder how it is legal to use stainless steel tubing that is not considered as electrical conduit and is not listed as such. Also, Can this tubing be welded to junction boxes as well as be welded were there should be a coupling. No bending is being done. Basically it is like plumbing lines the way it is. No ELECTRICAL FITTINGS.
Can someone tell me if i am missing something and this is a legal electrical practice. I can't seem to find anything in the NEC or UL codes.

 

[kwired]

Chapter 3 wiring methods all mention that the method they cover and it's associated fittings all need to be listed.

I have seen what you described as well, it is effective in food processing plants as polished welded connections does make sanitation issues better then fittings that have a crack for bacteria to grow in but is still not NEC compliant. FWIW good process piping welders do not leave much for abrasive issues on inside of pipe at their welds - the whole idea of the process they use is to end up with a smooth clean surface inside and outside the pipe to prevent having small cracks or other places for product to hang up in and allow for bacteria growth, so I don't personally have too much issues with the possibility of damage to conductors pulled through such a pipe, which I believe is one main reason raceways are not permitted to be welded in general.

 

[CTuttle]

Thanks for the response.

 

[petersonra]

one could argue that because the NEC is enacted and regulated at a state or local level that federal FDA good manufacturing practices can override them.

 

[just the cowboy]

cables or wires

cables or wires

What is in the pipe cable or wires? If cables could it be considered a sleeve.

 

[iwire]

What is in the pipe cable or wires? If cables could it be considered a sleeve.

I was thinking the same thing.

 

[ActionDave]

What is in the pipe cable or wires? If cables could it be considered a sleeve.

You would need some kind of connector for cable. That does not sound like what the OP has going on.

 

[iwire]

You would need some kind of connector for cable.

That depends on the use of the cable.

 

[gadfly56]

If you're using this as raceway, I'd probably not use it as a grounding means if otherwise allowed. IIRC, stainless steel is a particularly poor conductor of electricity (4X carbon steel) and might not be suitable.

 

[kwired]

If you're using this as raceway, I'd probably not use it as a grounding means if otherwise allowed. IIRC, stainless steel is a particularly poor conductor of electricity (4X carbon steel) and might not be suitable.

I don't see any objection in NEC to use true listed stainless RMC as an equipment grounding means. It may have a lower conductivity level then some other metals, but is still a pretty low resistance and is likely a pretty effective equipment grounding means. Probably better then loose EMT fittings are.

 

[gadfly56]

I don't see any objection in NEC to use true listed stainless RMC as an equipment grounding means. It may have a lower conductivity level then some other metals, but is still a pretty low resistance and is likely a pretty effective equipment grounding means. Probably better then loose EMT fittings are.

Well, OK. It's 40X less conductive than copper on an equal cross sectional area basis. If that's OK with the NEC then so be it.

 

[DougAles]

I ran into this a few times and i am wonder how it is legal to use stainless steel tubing that is not considered as electrical conduit and is not listed as such. Also, Can this tubing be welded to junction boxes as well as be welded were there should be a coupling. No bending is being done. Basically it is like plumbing lines the way it is. No ELECTRICAL FITTINGS.
Can someone tell me if i am missing something and this is a legal electrical practice. I can't seem to find anything in the NEC or UL codes.

I see you are in Wisconsin. Is this in Wisconsin?

Here is what happened in Wisconsin. Kurt Barnard, a electrical engineer with Excel Engineering in Fond du Lac, Wisconsin, a specifying engineering firm that has a strong food & beverage processing client base, wrote a pamphlet and submitted it to the state of Wisconsin requesting a variance. He succeeded at obtaining the variance and that is why you are seeing this in Wisconsin.

I know Kurt personally so if I can help you in any way, please feel free to contact me.

Note: Before posting this reply, I did call Kurt and got his permission to use his name in my explanation.

 

[iwire]

Well, OK. It's 40X less conductive than copper on an equal cross sectional area basis. If that's OK with the NEC then so be it.

But the areas of each are much different. This is why steel conduit can provide a lower impedance path than a copper EGC that would be pulled inside it.

 

[gadfly56]

But the areas of each are much different. This is why steel conduit can provide a lower impedance path than a copper EGC that would be pulled inside it.

Mmmm, OK let's see where this leads.

3/4" RMC is basically schedule 40 steel pipe. It has an OD of 1.05" and and ID of 0.82". The formula for area is Pi*r^2. The area of the annular cross section that is the steel itself is the area of the OD minus the area of the ID or Pi*(1.05/2)^2 - Pi*(0.82/2)^2 or 0.8659 - 0.5281 or 0.3378 sq in. Now since the stainless steel is 40x LESS conductive than copper, we divide 0.3378 by 40 to get the equivalent area of copper that would present the same resistance to current flow: 0.3378/40 = 0.0084 sq in. Solid #10 AWG copper wire has a cross sectional area of 0.0082 sq in which is just a hair under what we're looking for. If we were using mild steel pipe, you'd have a 4x advantage, and now you'd need something just larger than #4 AWG in copper to get the same impedance path.

In mild steel, conduit is the clear winner as an EGC; in stainless steel, not so much.

This of course says nothing about the contact area for any fittings in the conduit run, it's just assuming a straight shot of unbroken conduit vs a single solid copper wire. I have no idea what might happen once you start putting connectors, j-boxes, and couplings into the equation.

 

[jap]

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. Not that its the same type of weld , but, I've seen new muffler installations where the inside of the tailpipe looked like that game where you put a bunch of sticks across the tube and try to pull them out without dropping the marbles.

JAP>

 

[iwire]

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. Not that its the same type of weld , but, I've seen new muffler installations where the inside of the tailpipe looked like that game where you put a bunch of sticks across the tube and try to pull them out without dropping the marbles.

JAP>

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.

 

[iwire]

Mmmm, OK let's see where this leads.

3/4" RMC is basically schedule 40 steel pipe. It has an OD of 1.05" and and ID of 0.82". The formula for area is Pi*r^2. The area of the annular cross section that is the steel itself is the area of the OD minus the area of the ID or Pi*(1.05/2)^2 - Pi*(0.82/2)^2 or 0.8659 - 0.5281 or 0.3378 sq in. Now since the stainless steel is 40x LESS conductive than copper, we divide 0.3378 by 40 to get the equivalent area of copper that would present the same resistance to current flow: 0.3378/40 = 0.0084 sq in. Solid #10 AWG copper wire has a cross sectional area of 0.0082 sq in which is just a hair under what we're looking for. If we were using mild steel pipe, you'd have a 4x advantage, and now you'd need something just larger than #4 AWG in copper to get the same impedance path.

In mild steel, conduit is the clear winner as an EGC; in stainless steel, not so much.

This of course says nothing about the contact area for any fittings in the conduit run, it's just assuming a straight shot of unbroken conduit vs a single solid copper wire. I have no idea what might happen once you start putting connectors, j-boxes, and couplings into the equation.

Check this out.

http://steeltubeinstitute.org/steel...eettheNECRequirementsofEquipmentGrounding.pdf

 

[ActionDave]

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.

Absolutely. I did work in a gas plant with a ton of stainless pipe. The guys who could tig weld were very impressive.

 

[GoldDigger]

Absolutely. I did work in a gas plant with a ton of stainless pipe. The guys who could tig weld were very impressive.

I suspect that one key to avoiding a rough weld bead inside is using a fixture to hold the accurately cut ends together while welding.

 

[petersonra]

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.