[Lone Crapshooter]

Saw this at work. The job was to replace faulty heat tracing 10 watts per-foot. Someone else had troubleshot the problem. Looked at the job just over a year old the problem was local to a pump and about 30' total of piping. No controls other than a manual switch to turn the tracing on because the chemical will freeze at 70F.
The tracing was self regulating and it had gotten so hot that it had melted the tracing. I could not strip it with a knife because where the plastic components had not yet totally destroyed the outer sheath , the brade under the sheath, the black plastic spacing strands, the semiconductor heating and the power conductors were all fused together. The plastic standoffs that support the Chemlex splice box that sits on the top of the insulation GONE . Just 2 puddles of black plastic.
Had never seen this before I never knew that self regulating heat tracing would get that hot.

Replaced the old tracing and it seems to be working fine.
Any ideas as to what happened.

LC

 

[99cents]

What is your supply voltage? Does it match the voltage rating of the original cable?

 

[Lone Crapshooter]

120 volt supply voltage 120 volt cable.

 

[99cents]

Weird. Did the braid somehow become energized? I really don't know. There is suspicion that some manufacturers had problems with burn back on self reg after it was submersed in water for a long time. I don't know if it's true or not.

 

[don_resqcapt19]

Did they purge the pipe with steam? There was a large refinery job near here where they had to replace tens of thousands of feet of heat trace because the purged the piping with high pressure steam after the trace was installed.

 

[glen1971]

One of two things comes to mind.. Over exposure temperature would definately be one, as Don suggestted.. All heat trace has maximum exposure limits and if you exceed them, damage can occur..
The other one that I have seen in the past, and the trace was melted to the pipe and was next to impossible to strip was a small short in the circuit, and no GFI breaker to protect it.. No GFI, an oversized breaker or one that won't regularly trip at its rated ampacity (typcially older FPE pushin) could cause a meltdown...

 

[Lone Crapshooter]

I could see the steam purging being a issue but that is not the case here. No GFCI I will look or talk to my coworker. It is fed from a SQD panel.

 

[Loose Neutral]

Heat trace sucks.

 

[varmit]

I have seen and fixed melted heat trace several times. Usually the trace shorts to the pipe or fittings and there is no low resistance fault path to clear the breaker, so the heat trace sets there and destroys itself. (Think: A #16 wire with a high resistance ground and 120 volts.) I have seem some trace actually catch fire in this scenario. Often times a chemical leak causes the initial failure. If something over heats the pipe, by welding or thawing the pipe, this can cause the problem also.

A GFI can help with clearing the fault, but at chemical plants the home runs can often be very long in sometimes wet conditions. This can cause nuisance tripping if the GFI is located a long distance from the load. In a "perfect world" a local blank face GFI with a feedback indication to a heat trace monitoring panel is the way to go. A proper plant wide bonding of all piping and structures can help but is difficult and expensive to implement.

 

[99cents]

Heat trace sucks.

Yeah, a multi million dollar industry sucks.

Any other suggestions, almighty guru?

 

[Loose Neutral]

Yeah for you to suck it.

Yeah, a multi million dollar industry sucks.

Any other suggestions, almighty guru?

 

[Big John]

:lol:

 

[99cents]

Yeah for you to suck it.

I see the testosterone shots are working...

 

[Semi-Ret Electrician]

Since it's a chemical plant could it be exterior chemical attack? acetone etc?

 

[wcord]

Since it's a chemical plant could it be exterior chemical attack? acetone etc?

I thought that the Fluoropolymer jacket was supposed to be impervious to most chemicals?

 

[Semi-Ret Electrician]

I thought that the Fluoropolymer jacket was supposed to be impervious to most chemicals?

There are hundreds of chemicals that will attack it.

Could you dip a piece of the tracing in a glass jar of the chemical(s) in that area for a few weeks?