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Underground piping operating at temperatures significantly different from the ambient is commonplace. It seems natural that such pipes should be insulated to reduce heat transfer. Not everyone realizes that the earth cover makes a significant contribution to the total thermal resistance when the system is buried more than a foot or so and the soil is not water filled. Additional insulation needed to reduce the heat transfer to an economically acceptable value is, in many cases, very little. Unfortunately, the design of a buried line is not as simple as this statement implies because there are many problems connected with protecting the pipe from corrosion and the insulation from damage. These problems differ sufficiently for hot and cold lines so that it is not convenient to treat the two cases together. This paper deals with hot lines only, though many of the ideas are also applicable to buried cold pipes. It is further assumed that the pipe is buried two or more diameters under the surface and that the soil is sufficiently dry and compacted so that there is no convective heat transfer.
Research and Development Div., Pittsburgh Corning Corp., Port Allegany, Pa.