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Combined Loading of Buried Thermoplastics Pressure Pipes

 

Surface Loading & Deformation # 2004 Milan

This paper presents the results of work that was performed at the request of TEPPFA , The European Plastics Pipes and Fittings Association, on the issue of “Combined loading” (external and internal loading) of buried thermoplastics pressure pipes. The work is of great importance for users and designers of thermoplastics pipes. Quite often users are confused about the design of thermoplastics pipes, especially when the design is compared with traditional methods, originally developed for the design of buried linear-elastic pipe materials. Users of water mains for instance, demand a clear relation between the product pressure classification (PN) and the operational pressure (PFA) to be given in product standards. Tests have been performed to check if, and to what extent, tensile stresses induced by internal pressure shall be added to the tensile bending stress induced by external loading. Tests were performed on radially deflected as well as axially bent pipes. The time to failure was recorded. It was shown that the time to failure in these combined loaded pipe samples is the same as for straight non-deflected pipe subjected to the internal hydrostatic pressure only. Recommendations for the design of buried thermoplastic pipes both for pressure and nonpressure applications are given, based on the results found in this study.

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