The structural performance of flexible pipes

Abstract

High density polyethylene pipes have been used for over a decade but little information is available on the in-service behavior of these pipes. At the request of the Minnesota Concrete Pipe Association, an investigation to evaluate the field performance of HDPE was undertaken. The objective of the first part of this dissertation was to investigate the field performance of in-service HDPE pipes using visual information obtained from a remote, motorized video camera. Ten projects with a total length of 12,006 feet were investigated in Minnesota. The performance characteristics considered in this evaluation were cross sectional deformations, wall buckling, wall crushing, wall cracking, joint separation, and sediments. Few major structural problems were noticed due to the effect of granular material used as a backfill. CANDE is one of the commonly used programs for buried pipe analysis; however, the limitations of CANDE include application only to small deflections, and neglect the time effects. The recent tendency of using thermoplastic pipes for deep applications, which increased the need for investigating the effect of large deflections, and the dependency of the properties of such pipes on strain rate and time led to the use of ANSYS. The main advantage of CANDE relative to ANSYS is the use of the nonlinear soil models while ANSYS has the advantage of modeling large deflections. A computer code using ANSYS programming language was written to model the soil behavior using hyperbolic tangent modulus with both power and hyperbolic bulk modulus models. CANDE and the small and large deflection theories of ANSYS were compared with Moser's (1994) results. This comparison showed that CANDE over-predicts the pipe deflections as the soil approaches the shear failure and that ANSYS better describes the pipe behavior. CANDE can be used as long as the shear

A strain energy-based equivalent layer method for the prediction of critical collapse pressure of flexible risers

“…The more flexible the pipe is, the less its collapse resistance becomes. The critical pressure (maximum external pressure before collapse) of flexible risers does not only depend on the pipe material properties but also on pipe geometrical properties (Suleiman, 2002). Experimental tests could be an reliable approach to determine the critical pressure but such kind of the hydrostatic tests usually costly.…”

Pipe Stiffness Prediction of Buried Gfrp Flexible Pipe

“…When a flexible pipe deflects against the backfill, the load is transferred to and carried by the backfill. When loads are applied to rigid pipes, on the other hand, the load is transferred through the pipe wall into the bedding material 2 .…”