The influence of using CFRP wraps on performance of buried steel pipelines under permanent ground deformations

Abstract

In this study, using FRP wraps to reinforce buried steel pipelines under permanent ground deformations is investigated. For this purpose, carbon/epoxy composite wrap was used on API 5L grade X65 pipeline which is the typical material for oil and gas transportation pipelines. Mechanical behavior of the pipelines under strike-slip faulting was studied using nonlinear finite element code ABAQUS. The pipeline was supposed to be perpendicular to the fault plane. Proper performance criteria were used to determine critical fault displacements. According to defined performance criteria, critical fault displacements for different diameter to thickness ratios, various composite wrap thicknesses, and for both non-pressurized and pressurized pipelines were determined. Percentages of increase in critical fault displacements compared to non-wrapped conditions were calculated. In some pressurized pipelines, increasing strain in the ruptured area of composite wrap on the pipeline led pipeline to rupture at ultimate tensile strain of the pipe material. Results indicate that using 1-mm-thick composite wrap for non-pressurized pipelines leads critical fault displacement to increase about 100%. In addition, by increasing the thickness of composite wrap, the value of critical fault displacement increases significantly, so that applying composite wraps with thicknesses of 1 and 10mm on pressurized pipelines with diameter to thickness ratio of 144 caused critical fault displacement to increase by 154% and 892%, respectively. According to results of this research, using FRP wraps to reinforce buried steel pipelines under permanent ground deformations is recommended.