Heat Transfeer 2

[sigma1]

We have a very hot 12" diameter pipe (960 deg F) supported by the steel structure. Is there a way to determine the heat dissipation or how long the supporting steel has to be to avoid heating the structural steel.

 

[IRstuff]

You need to provide more parameters.

How hot can the structural steel be allowed to get to?

What are the emissivities of the pipe and the structural steel?

What is the airflow?

What is the ambient?

Can you put thermal shields on the pipe?

TTFN

FAQ731-376

 

[vpl]

Is the pipe insulated? (hint, hint)


Patricia Lougheed

Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of the Eng-Tips Forums.

 

[sigma1]

Yes the pipe is insulated and we will have to penetrate the insulation and jacket. My original question to my fellow structural ladies and gentelmen was: how to determine how much heat will dissipate if the support has a certain length, diameter, and thickness (assuming it will be a pipe). If I can determine the rate of dissipation I can size the support accordnigly.

Note: On several occasions I have seen these pipes with welded saddles at the bottom 120 degrees resting on steel beams existing or supplementary. I dont even want to thing what would happen to a hand that will touch the steel while the generator is running.

Thanks for your help.

 

[vpl]

I'm not a structural engineer (but, then, this is a heat transfer forum). If you're looking for structural engineers, you might want to try a different forum.

I know that there is a thermal component to calculating the loads seen by a pipe support. I believe that you will find the appropriate equations in the ASME Code. But, I'm not sure that dissipating the heat is really a consideration. After all, as per your example, sometimes those saddles are only a foot off the structural steel. But then I'm still scratching my head about why anyone would stick their hand on hot steel whether or not a generator is running and, other than the humanitarian consideration, why I would care.

Patricia Lougheed

Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of the Eng-Tips Forums.

 

[IRstuff]

The surface temperature limit isn't necessarily just for deliberate contact, it includes accidental contact, i.e., from a person falling and attempting to use his hand to stop or steady himself.


Even still, there's a range of temperatures that could be designed for.

National Burn Victim Foundation info:
160ºF --> 1 sec to 3rd degree burn
149ºF --> 2 sec
140ºF --> 5 sec
130ºF --> 35 sec
120ºF --> 10 min

The "correct" contact times are a bit uncertain; I've seen varying values for contact times.

Your specific question isn't necessarily easy to answer. The basic calculation involves:
> establishing an allowable surface temperature on the steel
> determining the heat flow given the thermal conductivity and temperature difference across the support
> determining whether the heat flow down the support can be dissipated from the steel, given whatever ambient conditions stipulated, like air temperature, surface area, etc.

TTFN

FAQ731-376

 

[sigma1]

VPL

I was not looking for structural engineers. I was looking for help there because they are the ones that deal with these type of pipes and supports. But they don't and that is why I posted the question on this forum because I assumed nuclear engineers like your self do know how to support a high pressure steam lines.

FYI. People dont stick their hands in hot steel.However, sometimes field personnel do try hold on to something that may be hot. OSHA, lawyers (hint, hint)

 

[EddyC]

Hello sigma,

I did a very crude analysis and used the following assumptions (among others):

a) temperature of pipe support at pipe/support interface = 1000 F
b) pipe support rests on a beam/column with pipe support mass 1/10th the mass of the local beam/column.
c) temperature at the ends of your local beam/column where it connects to the rest of your structure is 70 F

I get a temperature at the pipe support-beam/column interface of 160 F. This temperature will drop to 70 F as you move away from the pipe support to the remainder of your supporting structure. I don't believe that the 160 F will be of any concern to you in the design of your supporting structure. Hope this helps.

 

[sigma1]

Thanks EddyC

Do you mean the temperature at the interface between the pipe support and the supporting structure will drop down to 160 deg F and 70 degrees as you move away from that interface?

Since the mass is critical does length matter? Is it true that a longer pipe support member is better than a shorter one with the same mass. Is that assumption accurate?

Once again thank you very much!!

 

[EddyC]

sigma,

I am in agreement with you about the 160 F being at the interface and the 70 F being away from the interface.

I'm not sure how the length influences the results. I have neglected the effects of convection and radiation, and am using only conduction. This should be conservative.

Regards.