External Temperature of Steel Pipe in Air. 1

[Neocorr]

I am looking for a rule of thumb that will dictate whether the surface temperature of an uninsulated steel pipe in air will be a similar temperature to the temperature of the fluid in the pipe (in particular, well emulsion lines prior to their entering the ground). I know that this depends on several factors, and is not a trivial problem to solve accurately. But, if anyone has any practical experience dealing with this issue and is able to give me some advice I would really appreciate it.

 

[KernOily]

Ahh, finally, another oil patch facilities engineer... I was beginning to think I was the only one on the forum here... ;-)

Here's what I've found from field measurements. The temperature drop across the pipe wall varies with temperature (duhhh...). In field measurements of a vessel with a deep thermowell, using a digital handheld TI, not an infrared gun, we found that for a 8' Ø, 3/8" wall vessel operating at 250° internal temperature, the vessel wall temperature was about 12° less, or 233°. This was on a still day with ambient T at about 60°.

For steam lines, I use the rule of thumb that the pipe surface temp is about equal to the fluid process temp inside the pipe. This is plenty accurate enough for your heat loss/insualtion calcs.

For production lines I have sort of linearized my field measurements, i.e. if the pipe surface T is about 150°, I've assumed the internal T is about 155° or so. This will be plenty close enough for your fluid and transport property calcs since that is usually well past the point that the crude viscosity curve takes off exponentially, at least for heavy crudes (13.5° API).

The process engineering text I refer to frequently says that you can usually assume that the fluid temperature inside a pipe is about the same as the pipe external temperature "within a reasonable error margin". I guess you are the one that gets to define what a reasonable error margin is. My field measurmements tend to back this up. Thanks!
Pete
P. J. (Pete) Chandler, PE
Principal Engineer
Mechanical, Piping, Thermal, Hydraulics
Processes Unlimited International, Inc.
Bakersfield, California USA
pjchandl@prou.com