Inspection/Testing of Conduit Seals (aka Seal-Offs)

[CheMechanical]

Earlier this year we had an incident where failed conduit seals allowed natural gas to seep from a classified location into an electrical panel in an unclassified area, which caused an explosion. The seals appear to have been improperly installed (bunched wires) and have all been replaced.

I'm writing a procedure for my company to implement a new policy for 100% visual inspection of conduit seals to ensure wires are properly separated and the seals properly poured to minimize the chance of this happening again.

I know that conduit seals are not perfect, but I'd like to include a procedure to test seals to verify they are installed properly. One of our electrical engineers said we could use water and let it sit for a few minutes to see if there is significant leakage, but that usually they are just visually inspected. He said that the water could be removed with a paper towel and that the small amount of water that might seep through the seal is inconsequential.

My question for the forum is whether there is an established procedure for testing conduit seals using water (or similar) which I can refer to in my instructions. I understand from looking at other threads that helium detection and pressure tests are also options, but I would prefer something simple that requires minimal special equipment. OTOH, we need to do this properly if we're going to do it at all.

BTW, I'm not cutting out the EE; he's just really busy and doesn't have time to write this procedure so this is the fastest way to get it done. My intention is to finish the draft instructions and route it to our electrical engineer and other folks for review/comment.

 

[itsmoked]

I would think a very reliable way would be to put a single drop of something like perfume or Percapton on the joint on the clasified side and see if you can smell it on the safe side. Smelly chemicals can be detected at insanely low levels by humans, (ppm). If you end up smelling it on the safe side for ANY reason, like it came thru somewhere else, you would know you have work to do.

 

[stevenal]

Seal both ends of conduit run. Use tee, reducers, etc, to install pressure gauge and schraeder valve. Pressurize the conduit and watch gauge. Leave conduit pressurized to see if any failure occurs in the future. Use a low enough pressure so the procedure itself along with heat from loading does not cause a failure. I've never done this, just thought I'd throw it out there for others to shoot down.

 

[itsmoked]

I like it.

A lot of ultralight builders put schrader valves and small gauges into the aircraft frames then leave them pressurized with a few psi. This keeps the moisture out of the inside of the frames and instantly detects cracks.

Having wires running in and out does increase the complexity of this scheme tho.

 

[resqcapt19]

I'm not sure that perfume or pressure testing will work. Look at the FPN after 501.15 in the 2005 NEC.

FPN No. 1: Seals are provided in conduit and cable systems to minimize the passage of gases and vapors and prevent the passage of flames from one portion of the electrical installation to another through the conduit. Such communication through Type MI cable is inherently prevented by construction of the cable. Unless specifically designed and tested for the purpose, conduit and cable seals are not intended to prevent the passage of liquids, gases, or vapors at a continuous pressure differential across the seal. Even at differences in pressure across the seal equivalent to a few inches of water, there may be a slow passage of gas or vapor through a seal and through conductors passing through the seal. See 501.15(E)(2). Temperature extremes and highly corrosive liquids and vapors can affect the ability of seals to perform their intended function. See 501.15(C)(2).

 

[itsmoked]

resqcapt19; Nice reference. About what I'd expect. The system/facility has to be designed such that a few ppt isn't going to cause problems in ajacent areas anyway or positive pressures and other methods would be required.

 

[stevenal]

Certainly an argument against using my method above as a continuous test on equipment not specifically designed to be continuously gas tight. Doesn't argue against using it as an initial test or as a spot check, though. Tires gradually loose pressure too, but even a slow leaking puncture can be distinguished with a pressure check.