Relief Systems – Solar Heat Effects and Considerations

The amount of solar energy a pipe line may absorb and the effect on the pressure build-up from expansion will be essentially the same at all geographic locations between 60°N and 60°S latitudes.

Directional orientation between latitudes 60°N and 60°S does have an effect on the total amount of heat that can be absorbed by a pipe line. A North-South line will absorb more heat than an East-West line, but the maximum rate of heat absorption (at noon) is the same for both.

Wind affects the heat lost by a pipe from convection currents. Wind of 10 mph will double the convection heat losses from bare pipe in still air. Since still air is a possibility at all locations, the theoretical maximum temperatures attainable from solar heating have been calculated assuming natural-convection heat losses without any wind. (See Section 900 of the Fluid Flow Manual for wind heat transfer coefficients.)

Paint and pipe coating will affect the amount of heat a pipe line can absorb from solar radiations. Most light colored paints will reflect 20 to 30% of the solar energy, but only on freshly painted surfaces. Since a line could be painted any color after its initial installation, the theoretical maximum temperatures attainable have been calculated assuming flat-black painted lines with an absorptivity of 1.0.

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