(5) Steady-state thermal influences in iso-

period can be calculated from the heating index

during that period (see paragraph 12.9*h*):

tropic, homogenous soils can be summed and geo-

metric modifications and approximations can be

made to the basic steady-state equations. For

example, a layered soil can be represented by an

"effective" soil thickness with the same total thermal

resistance as the layered soil. When pipes are buried

below the area influenced by short-term air

temperature fluctuations, the ground temperatures

around the pipeline resemble a slowly changing

series of steady-state conditions. The heat loss from

where

deeply buried pipes can be calculated from steady-

I = heating index EF (time period).

state equations for a cylinder of material around a

R = thermal resistance hrftEF/BTU.

pipe if the fluid temperature and the soil temperature

at a known distance from the pipe are measured,

and the soil and insulation thermal conductivities are

known. Heat loss from deep pipes can also be

freezing or thawing of soil and the ice thickness on

conveniently estimated by replacing the ground

water bodies are best obtained by field

surface temperature in the steady-state equations

measurements, but they can be estimated using one

with the undisturbed ground temperature at the pipe

of the many analytical solutions available. Because

depth. Heat loss from a buried pipe over a time

of the assumptions necessary in these analytical

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