Use of Fiber Bragg Grating Strain Gages on a Pipeline Specimen Repaired with a CFRE Composite System

Abstract

Re-establishing the maximum operating pressure of a segment of pipeline with metal loss defects, such as erosion or corrosion defects, can be accomplished either by replacing the damaged segment altogether, or by applying a localized repair system. The present paper deals with laboratory tests conducted: (1) to understand and describe how the reinforcement layers of a carbon fiber epoxy composite material can enable a steel line pipe specimen with a metal loss defect to withstand pressure loading; (2) to compare the test results with those predicted by Mechanics of Materials and by Finite Element numerical solutions developed previously. Hydrostatic burst tests were performed on three pipe (API 5L X65 ERW) specimens: one with metal loss defect, one without metal loss defect, and one with metal loss defect but repaired with a carbon fiber reinforced epoxy composite system CFRE. Fiber Bragg grating FBG strain gages were used to monitor elastic and plastic strains during the tests of the repaired specimen. The strain gages were bonded either directly on the surface of the defect, or were inserted in between some of the composite layers in order to show the reinforcement’s effective contribution to the strength of the repaired pipes. The analytical and numerical results agreed very satisfactorily with experimentally determined burst pressures and pressure-strain curves, showing that the behavior of composite reinforced pipelines can be well predicted by using simple Mechanics of Materials or sophisticated Finite Element solutions.