Caustic resistant wire and conduit?

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MattG0311

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Illinois
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Apprentice Wireman
Hi all,

Worked on a motor this week in a hydrochloric acid containment pit. Small three HP motor was grounded out and being replaced. Upon removing the sealtite, it was clear the acid had worked its way inside and continued through the conduit rotting it from the inside out. The conduit used was vinyl coated rigid, however the inside enamel coating did nothing to stop the corrosion. Wiring off motor back to the first fitting about 8ft away also was also megging to ground so it was replaced as well. I think fiberglass or pvc conduit would be better in this environment. Anyone know of a wire that is resistant to extremely caustic conditions? Previous appeared to be THHN/THWN-2. Replaced it with the same thing. Don’t ask about stopping the acid leaking...out of our control besides maybe a different conduit run. Safety rangers don’t fret, we were in full chemical exposure suits. It was amazing how fast that stuff will corrode your tools though!
 
Can’t answer for your wire situation. But if it were me I would install a seal off right next to the motor terminal box, that away even if it gets in the raceway again it can’t enter the motor.
 
petersonra said:
Is Teflon insulated wire in chapters 3 somewhere?
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Yes, TFE.

It’s usually used for the higher temperature properties. I’d go for the pure Teflon version though not the fire alarm blends. The only hassle is that it’s tough to strip but pulling it is a breeze.
 
210626-2007 EDT

Other interesting characteristics of Teflon are:

(1) It is not real flexible, but it is a good insulator in thin sections, and requires no plasticizer to be adequately flexible. Thus, nothing to leach out from immersion in oil. PVC requires a plasticizer for flexibility, and when saturated with oil becomes brittle.

(2) Teflon is a thermal plastic with a high melting point.

(3) Teflon is not inexpensive.

.
 
THHN/THWN is nylon coated PVC insulation. The copper inside is still copper.

As mentioned fiberglass or PVC raceways should withstand the corrosion, but that don't mean things can't get inside. I think cables with glands is likely better deal than flex to motors and other items. They may still allow transmission but will be lesser and take longer to migrate through.

There is also stainless raceways and enclosures. Also stainless body motors are available though the magnetic core will still be mild steel.
 
Never saw Teflon but I have seen XHHW in a lot of corrosive environments. It seemed to hold up well. I think you can get a version of it with nickel plated copper conductor but not certain.
 
jmellc said:
Never saw Teflon but I have seen XHHW in a lot of corrosive environments. It seemed to hold up well. I think you can get a version of it with nickel plated copper conductor but not certain.
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You probably have but don't realize it. Some fixture wires and machine tool wire is teflon.
 
kwired said:
THHN/THWN is nylon coated PVC insulation. The copper inside is still copper.

As mentioned fiberglass or PVC raceways should withstand the corrosion, but that don't mean things can't get inside. I think cables with glands is likely better deal than flex to motors and other items. They may still allow transmission but will be lesser and take longer to migrate through.

There is also stainless raceways and enclosures. Also stainless body motors are available though the magnetic core will still be mild steel.
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Conduit by definition is not and does not need to be sealed, except for installing glands. That’s why plumbers use pipe door or anaerobic thread sealants. Robroy SOUNDS good but in practice still not sealed. And rigid right to a motor…maybe but usually not a good idea.

Mild steel is reasonably resistant to high pH. But PVC: have you actually seen what it does to it? It gets extremely brittle. If you are really going down this route PVDF (Kynar) IS highly resistant to bases and is somewhat more expensive and recently approved. The big truck is solvent welding doesn’t work. Like HDPE you heat it with an iron and weld it together. VERY solid connections.

Caustic on metals is a strange animal. It doesn’t so much corrode it like acids as it just sort of dissolves away. This is speaking from experience working at lots of chemical plants and lime plants.
 
High PH and bases? Where did caustics enter the discussion?

TFE with nickel wire might be the ultimate but is it needed? IMHO the goal should be to keep the fumes out of the raceway.
 
Russs57 said:
High PH and bases? Where did caustics enter the discussion?

TFE with nickel wire might be the ultimate but is it needed? IMHO the goal should be to keep the fumes out of the raceway.
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Read OP: caustic…

At least caustic, soda ash, lime, and most other alkalis don’t tend to generate fumes quite like say sulfuric, hydrochloride, or nitric acids. It tends to be more of an issue that they leave precipitates everywhere. Dry material is fairly innocuous but if it’s wet it becomes very reactive.

Nickel isn’t that much more caustic resistant than copper. It is usually added in small amounts (a few percent) for heat, not corrosion. Corrosion protection has more to do with chrome or gold.
 
"Worked on a motor this week in a hydrochloric acid containment pit"

I figured the "Anyone know of a wire that is resistant to extremely caustic conditions" was a mistake in wording. I disregarded it to such a degree I didn't even remember him saying it. My bad. Regardless I think we are talking acid here.

PVC and rubber would be acceptable, are cheap, and readily available. Stainless isn't a good choice. If metal must be used, best to use a high nickel content alloy. That stuff isn't cheap. I have paid for Inconel before.
 
Russs57 said:
"Worked on a motor this week in a hydrochloric acid containment pit"

I figured the "Anyone know of a wire that is resistant to extremely caustic conditions" was a mistake in wording. I disregarded it to such a degree I didn't even remember him saying it. My bad. Regardless I think we are talking acid here.

PVC and rubber would be acceptable, are cheap, and readily available. Stainless isn't a good choice. If metal must be used, best to use a high nickel content alloy. That stuff isn't cheap. I have paid for Inconel before.
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I caught that as well and was like you just mentioned both ends of the spectrum. Not that I never run into both ends, food processing plants use both caustic and acid products for cleaning purposes as well as additives to products to change pH levels or other purposes during production.

The storage areas might be where you find the extreme effects of these, the production area they are usually diluted enough that PVC and stainless are not deteriorating at a significant enough rate to consider alternatives.
 
If I had a serious situation where I wanted to ensure proper corrosion mitigation, I’d hire an NACE certified engineer to design the solution.
 
Well, in additional to being involved with water treatment I dealt with a medical waste incinerator for several years. It produced a lot of acid so we used a lot of caustic to neutralize it. You had to be careful about materials used.
 
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