Heat Transfer Down an Empty Steel Pipe 2

[ChemicalJasper]

Help!

I need to calculate the heat transfer down a steel pipe, any ideas on how to do this please?

We are replacing a section of line, using a Stopple and bypass. The steel line contained a Hydrogen rich stream and where the new flanges are to be welded, the line requires a Hydrogen bake-out before welding.

Due to space constraints there is only 700-750 mm between the stopple and bake-out heating element. How do I work out if the heat from the bakeout will reach and effect the integrity of the stopple?

The heat will be applied using 2 x 6" wide 45 Amp, 65 volt heating elements at a temperature of 400 C. the pipe is 6mm CS and 6" ID.

Any hints or tips will be greatly appreciated.

 

[prex]

Look at thread391-200151 for the temperature distribution along the pipe.
Assuming the pipe inner wall is not exchanging (but you can use a fan to recirculate some air), and if my numbers are correct, you get n=[√](hP/kA)=5.7 m^-1. This means that in only 1/5.7=0.17 m = 170 mm the temperature difference with respect to ambient is reduced to about 1/3, and that at 700 mm distance the temperature increment is of a few degrees.

prex

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[ChemicalJasper]

Thank you very much Prex

Great advise!

 

[StoneCold]

You have to factor in the lenght of time that you are heating the pipe. I don't have an equation for you but I do have a lot of experience with hot objects from welding and the solution will be time dependant. The longer you heat one end of the pipe the further the higher temperatures will creap down the pipe. There is obviously a limit based on the heat loss of the pipe in open air but I think the solution is a little more complicated than prex has pointed out.