Design procedure for uncased natural-gas pipeline crossings of roads and highways

A method for designing uncased natural-gas pipeline crossings of roads and highways is presented. The procedures used are not new, but are adaptations of techniques that have been thoroughly tested and validated. The method involves a combined calculation of the internal hoop stress in the pipe that results from the operating pressure of the pipeline and the external stresses that result from dead load, live load, and impact loading. The internal stress is calculated by the Barlow formula, and the external stresses are calculated by the Spangler formula, which incorporates the Marston theory for the calculation of dead load and the Boussinesq point-load theory for live load. A brief resume of the history of the use of cased pipeline at highway crossings is given to explain the reasons for using it is the past. Advances in the technology of steel making, pipe manufacture, pipeline construction, nondestructive inspection, pressure testing cathodic protection, and maintenance inspection are listed to support the increased use of uncased pipeline. The improved cathodic protection of the carrier pipe that is available in uncased crossings is given as the primary justification for their use. /Author/