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Old 09-03-2019, 07:49 PM
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Natural gas line question - max temp?

So... I am wondering what the maximum temperature is for a low pressure indoor NG line? I have a line to my pipe warmer that runs under my GH - I noticed today that it got pretty hot (I was not running the pipe warmer). I hit it with my laser probe and it was reading around 200f. How hot is too hot?
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Old 09-03-2019, 09:09 PM
Eben Horton Eben Horton is offline
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That would make me nervous and I would place some sheet metal between it and the heat source.
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Old 09-03-2019, 09:17 PM
Rick Kellner Rick Kellner is offline
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Will be interesting to see what code says, but anything above around 140 sounds kind of concerning to me.
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Old 09-04-2019, 03:26 AM
George Vidas George Vidas is offline
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if there isn't a leak, and if your gas line is made of metal and won't spring a leak at that temperature, it won't* ignite, because:

A) the autoignition temperature of natural gas is 1076F: https://www.engineeringtoolbox.com/f...res-d_171.html

B) because it needs to mix with air to be combustible. https://www.engineeringtoolbox.com/e...its-d_423.html

*: you should still investigate your worries and building codes.

Last edited by George Vidas; 09-04-2019 at 03:28 AM.
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Old 09-04-2019, 08:55 AM
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When I was studying the temperatures needed for pyrolysis to occur back in the fire dept days, I had thought 165 acceptable. Then I switched after looking at a lot of data. I dropped down to 135F as acceptable.

My point here won't be about the natural gas. It needs a 9/1 ratio to ignite. My concern would be with what other flammables like electrical wire are in that same environment. Insulation cracks and fails and an electric arc doesn't need a fuel ratio to cause damage,

I really try to keep all combustibles out of the hood and monitor the ones that have to be there. Don't have wiring above your tooling, period. The failures on the cable for moly's has just as much to do with the general heat atop the furnace as it does with the internal heat generated.
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Old 09-04-2019, 10:58 AM
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The temp does make me nervous. If I went with sheet metal - I should also add insulation correct so I am not just making a radiator? Regarding insulation, any recommendations on a good thin material?

My new shop space is very small and tight. Luckily it is masonry construction.
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Old 09-04-2019, 11:17 AM
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you would be making a radiator. I think the strip insulation sometimes used on water pipes is both thin and should be effective. Don't use paper backed stuff.
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Old 09-04-2019, 11:22 AM
Rick Kellner Rick Kellner is offline
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What about some of that dip lag type stuff? Like a rewettable fiberglass pipe lagging, over your insulation of choice. Hardens up when it dries out. Rated up to 1000 f.

This just happens to be the first one that popped up in a search:

https://www.buyinsulationproductstor...-pipe-lagging/
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Old 09-04-2019, 11:22 AM
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A search through the archives led me here:

https://www.jm.com/en/hvac/duct-board/

Still an ok product?

Pete - are you talking about the stuff used on boiler pipes? It is split I believe.
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Old 09-04-2019, 11:32 AM
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No, I think that stuff is flammable. I was thinking about yellow fiberglass in thin strips that I've seen used wrapping pipes. You could cut some strips of fiberblanket as well. It may also be that you need some air movement as well. That takes me to those little fans you see in computer cases.

You could approach it from the other end and get some insulation under the gloryhole after allowing for a dead air space.
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