Welded Sanitary Tubing Used as Conduit

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BrentB

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Location
Fort Collins, CO, United States
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Engineer
I toured a dairy plant recently that used welded sanitary tubing as electrical conduits (Raceway). All the connections to junction boxes and panels used tubing, those connections were also welded. Although I see the advantage from a waterproofing and sanitary design perspective, (bacteria love small crevices like threads,) I don't see how this could be called compliant to NEC section 300.18B, and sanitary tubing is not an approved raceway. The plant claims that the local AHJ has toured the plant and not raised the issue. Could the local AHJ actually approve something that is in conflict with the Code? Discussions with the plant electrician said that the practice is not uncommon in several of the local dairy plants. I don't want to stir up a hornet's nest, but I can't write up an installation spec for something that I consider non-compliant. Any thoughts?
 

GoldDigger

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Placerville, CA, USA
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Retired PV System Designer
I might have a practical concern about the electrical conductivity of stainless steel tubing if no wire EGC is used. I have not run the numbers as I do not know the wall thickness.
 

synchro

Senior Member
Location
Chicago, IL
Occupation
EE
I don't have a copy of the standard, but UL 797A edition 3 for aluminum and stainless EMT has "certification requirements for raised surfaces (beads) on inside of tubing." UL 6A might also have requirements for the interior surface of stainless RMC.

As an example of this issue, galvanized pipe for plumbing often has a significantly raised weld bead with sharp edges that could cause insulation damage if wire was pulled through it. That being said, a relatively large electrical supply house once told me that they don't stock rigid conduit nipples because everyone just uses the ones made for plumbing (I hope not). :(
 

hbiss

EC, Westchester, New York NEC: 2014
Location
Hawthorne, New York NEC: 2014
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EC
At the very least they do make stainless steel rigid conduit.

Sounds like the guys who do the piping are also installing the conduits? Not sure how the sizes run with "sanitary tubing" either so how would you size it? I also would have an issue with the finish of weld in the inside of a box where the conduit enters.

The plant claims that the local AHJ has toured the plant and not raised the issue.

I think I would give him a call and ask why the method is being accepted.

-Hal
 
Stainless process piping as used for food and pharmaceuticals manufacture is generally seamless, quite smooth inside, and weldable (friend is a retired pipefitter and built pharma plants); has to be so they can keep it really clean.

Was the SS tubing being used as a raceway or as a sleeve for cables?
 

BrentB

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Location
Fort Collins, CO, United States
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Engineer
Sanitary tubing (used for process fluid) is always welded or has tri clamp sanitary connections.
So what do their manufacturers say about weldability? 300.18(B) just requires that the product be designed to be weldable, not that it have a special listing.

Cheers, Wayne
The issue is sanitary tubing is not a raceway as defined in article 110. "Raceway . An enclosed channel designed expressly for holding wires, cables, or busbars with additional functionality as permitted in this code". Sanitary tubing (process piping) is designed for process fluids and is not one of the listed methods described in articles 342-366. The way I read code you can't use sanitary tubing as a raceway and unless welding is specifically covered in one of the articles. You can certainly get SS conduit and fittings that are listed but welding is not one of the allowed installation methods for "connection." REviewing individual raceway requirements, all of them have to be listed components.
 

BrentB

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Location
Fort Collins, CO, United States
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Engineer
Stainless process piping as used for food and pharmaceuticals manufacture is generally seamless, quite smooth inside, and weldable (friend is a retired pipefitter and built pharma plants); has to be so they can keep it really clean.

Was the SS tubing being used as a raceway or as a sleeve for cables?
As a raceway
 

BrentB

Member
Location
Fort Collins, CO, United States
Occupation
Engineer
At the very least they do make stainless steel rigid conduit.

Sounds like the guys who do the piping are also installing the conduits? Not sure how the sizes run with "sanitary tubing" either so how would you size it? I also would have an issue with the finish of weld in the inside of a box where the conduit enters.



I think I would give him a call and ask why the method is being accepted.

-Hal
In this case, the plant didn't say it was accepted, just the AHJ never called it out welded sanitary tubing used as a raceway as an NEC violation. It shouldn't have been missed (in my opinion) but in a plant with lots of sanitary tubing for process fluid piping it may have been overlooked by the AHJ as just additional process piping. Being a consultant, I don't want to open up discussions between the plant and the local authority when it is not part of the job I'm bidding on, I just went to get my pricing and installation specs correct. In this case, I don't see a way to meet code and comply with company practices.
 

wwhitney

Senior Member
Location
Berkeley, CA
Occupation
Retired
Sanitary tubing (used for process fluid) is always welded or has tri clamp sanitary connections.
My question had been about stainless RMC. If the manufacturer of that says it's weldable, then it's a raceway that complies with 300.18(B) that might be acceptable to the plant.

Otherwise, I would think the plant's path to NEC compliance would be to get the AHJ to judge that under 90.4 the sanitary tubing is an acceptable substitute for RMC and may be used as such. Then since the manufacturer obviously deems the sanitary tubing to be suitable for welding, it complies with 300.18(B).

Cheers, Wayne
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
It's pretty common in the food and dairy industry to weld fittings on the side of a stainless steel box. Might not be strictly to code but the important thing and that environment is not meeting the technicalities of the code but making the thing hygienic enough that you don't give somebody food poisoning. There's no way to adequately clean threaded pipe or threaded conduit for that matter.
 

BrentB

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Location
Fort Collins, CO, United States
Occupation
Engineer
My question had been about stainless RMC. If the manufacturer of that says it's weldable, then it's a raceway that complies with 300.18(B) that might be acceptable to the plant.

Otherwise, I would think the plant's path to NEC compliance would be to get the AHJ to judge that under 90.4 the sanitary tubing is an acceptable substitute for RMC and may be used as such. Then since the manufacturer obviously deems the sanitary tubing to be suitable for welding, it complies with 300.18(B).

Cheers, Wayne
An interesting thought. A couple of quick phone calls to SS RMC manufacturers didn't yield any information that said they manufactured the product with the intent weld. They are "checking.
It's pretty common in the food and dairy industry to weld fittings on the side of a stainless steel box. Might not be strictly to code but the important thing and that environment is not meeting the technicalities of the code but making the thing hygienic enough that you don't give somebody food poisoning. There's no way to adequately clean threaded pipe or threaded conduit for that matter.
I agree but the conduit (thread) is not a product contact surface. I think the welding was as much a waterproofing method as it was a sanitary design compliance method. Welding to junction boxes and panels is, in my opinion, inherently difficult to do well, due to the tight clearances inside the boxes and the need to remove internal components before the welding is complete to prevent weld spatter from ending up on unintended surfaces. That said the quality of weld that I could see was good but it would not comply with the surface finish requirements of pipe in dairy applications, sometimes as low as RA 0.5. There is just no way to polish welds inside panels and junction boxes effectively.

In my opinion, this situation probably evolved by somebody with a good background in (the arduous) Dairy Industry Sanitary requirements, setting an installation standard. Threaded connections in piping are never used (or allowed) and whoever set the standard just expanded a food contact/piping standard to conduit installations by stating the plant did not allow threaded connections. That plant standard bumped up against the NEC requirements but those requirements just weren't understood. I have seen threaded SS RMC in dairy and meat plants used successfully, but the craftsmanship in the assembly of the conduit has to be excellent. They wash down everything with high-pressure hoses on a daily basis. Circling back to the beginning of this discussion, I'll spec threaded SS RMC and work on getting the installation details and inspections well documented.
"
 

winnie

Senior Member
Location
Springfield, MA, USA
Occupation
Electric motor research
Why not ask the AHJ what their specific requirements are to permit the welded raceway?

Do you honestly believe that this plant's existing installation is hazardous? Or do you believe that it is 'practically safeguarded' simply not described in code?

I would be concerned about grounding impedance, damage to conductors from sharp edges, damage to enclosures due to the welding process, and radius or number of bends in the conduit. But each of these issues can be addressed if the designer/builder of the conduit system knows about them.

IMHO sanitary tubing used as an electrical raceway is not inherently unsafe, the biggest problem being that a system is being invented from scratch by people who might not know the nuance of electrical installations.

Plumbing elbows and electrical elbows are similar, but are very different in details. But I would expect a sanitary pipefitter to be able to weld pipe suitable for safe wiring if the differences were spelled out.

Jon
 

BrentB

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Location
Fort Collins, CO, United States
Occupation
Engineer
Briefly, no I don't believe it is hazardous, just not code compliant. All of the valid issues you raise are difficult to establish after the installation and at best nuanced, for the application of non-listed materials for an electrical installation. Pipefitters can weld top almost any requirement, but to get a crew doing things consistently correctly for another trade would be in my opinion, difficult. If the plant runs into a compliance issue with the current installation and is cited or called out, wwhitney called out a possible path above. I find AHJ's to be more difficult when confronted with an issue after the fact vs collaborating with the installers/designers to address a specific issue or outage in the current code before the installation.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
There have been a couple cases of contamination that was traced to microbes growing in a plant but not inside the process piping.

A lot of food places no longer allow standard enclosures because they can't be properly cleaned. The enclosure manufacturers now sell enclosures that can be cleaned. They have sloped tops and lips over the doors so water does not pool and the gaskets are made so they shed water too so no bacteria can grow there.

SS conduit that is threaded does not solve the problem of the nooks and crannies that are present where microbes can grow. Threads of any kind are pretty much uncleanable so the only way to deal with them is to get rid of them.
 

steve66

Senior Member
Location
Illinois
Occupation
Engineer
If the tubing isn't a raceway, then just pull in a cable instead of building wire. It could be either single conductor cable, or multiconductor cable.
 

gadfly56

Senior Member
Location
New Jersey
Occupation
Professional Engineer, Fire & Life Safety
An interesting thought. A couple of quick phone calls to SS RMC manufacturers didn't yield any information that said they manufactured the product with the intent weld. They are "checking.

I agree but the conduit (thread) is not a product contact surface. I think the welding was as much a waterproofing method as it was a sanitary design compliance method. Welding to junction boxes and panels is, in my opinion, inherently difficult to do well, due to the tight clearances inside the boxes and the need to remove internal components before the welding is complete to prevent weld spatter from ending up on unintended surfaces. That said the quality of weld that I could see was good but it would not comply with the surface finish requirements of pipe in dairy applications, sometimes as low as RA 0.5. There is just no way to polish welds inside panels and junction boxes effectively.

In my opinion, this situation probably evolved by somebody with a good background in (the arduous) Dairy Industry Sanitary requirements, setting an installation standard. Threaded connections in piping are never used (or allowed) and whoever set the standard just expanded a food contact/piping standard to conduit installations by stating the plant did not allow threaded connections. That plant standard bumped up against the NEC requirements but those requirements just weren't understood. I have seen threaded SS RMC in dairy and meat plants used successfully, but the craftsmanship in the assembly of the conduit has to be excellent. They wash down everything with high-pressure hoses on a daily basis. Circling back to the beginning of this discussion, I'll spec threaded SS RMC and work on getting the installation details and inspections well documented.
"
In order to meet clean-in-place protocols, I believe that such facilities have to minimize all potential sources of contamination. While the threads might not be a direct contact surface, I'm sure there is dust, spatter, and aerosolized product that could lodge in any exposed threads. In addition, these areas are usually subject to high pressure washdown (hence, clean-in-place), and threaded connections are not typically water tight.
 
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