Mechanical Behavior of Large Diameter Flexible Pipes Subjected to External and Internal Loading

Abstract

The production of power is of prime important now a days for industries as well as domestic purpose. In thermal power plants, different sizes of pipes are used to transfer the water and steam for process from one place to another. Those lines may be lying above ground or buried (underground).

This dissertation illustrates the structural design of large diameter buried pipeline in thermal power plants, where catastrophic failure is not affordable due to vacuum, due to increase in external loading and due to loss of soil support.

The work focuses on developing analytical approaches to predict behavior of flexible pipes (steel pipes) based on predetermined pipe properties, anticipated soil properties and various operating and loading conditions. The mechanical behavior of flexible pipes is also governed by specific installation configuration. Various load cases like external loading (above ground pipes), internal loading, the influence of live load on back filled surface (buried pipe), pipe deformation during back filling, check for buckling, check for collapse pressure, soil-pipe interaction, external loads, seismic etc. have been studied to see the behavior of large diameter flexible pipes.

Buried pipes may sometimes subjected to typical condition of loosening of support due to various reasons like water seepage, near site excavations etc. Such conditions may create circumferential buckling which may prove fatal for proper operation. Due to unavailability of analytical formulations for such loading condition in the governing pipe design standards, the finite element approach has been used to evaluate the behavior of the pipe. Finally an excel utility has been developed to facilitate the user for selection of large diameter flexible pipes for specific applications considering the effect of above said load cases.