Damage Characterization and Rehabilitation of Fiber-Reinforced-Polymer (FRP) Composite Pipes under Low Velocity Impact.

Composite pipes are gradually replacing the conventional pipes in the industrial applications due to their superior mechanical and thermal properties. However, the frequent failure of composite pipes caused by the mechanical damages is one of the important aspects that need to be addressed. The structural failure of these pipelines can be due to a number of reasons, such as burst, impact, puncture, overload, buckling, fatigue and fracture. These pipes are often very susceptible to foreign object impact during service. These damages can be vulnerable and can go unseen especially in case of low velocity impacts since these are not visually observable. A small dent caused by such impacts can lead to significant underlying damages for example, delamination, matrix cracking, fiber breakage and fiber/matrix interfacial debonding induced within the laminate. It is not always desirable to replace the pipeline with such non-leaking defects due to economic and technical reasons; rather it is preferred to verify its fitness for service. The fitness for service may or may not include remedy of a pipeline containing defects. The decision is made on the nature and severity of the damage. If the decision is to reinforce the defected region then an in-filed repair of the pipe is carried out. However, several challenges need to be met to obtain the desired repair quality. The major considerations are surface preparation, reduction in operating pressure for the repair, the duration required (e.g. for curing of the composite material) for the composite repair to share the load from the pipe, and the most important is the in-field quality assessment and to ensure consistency between several repairs. For this reason, extensive research needs to be carried out, on topics such as, foreign object damage, damage tolerance, impact loading and residual strength, damage characterization, damage classification, damage repair, and related issues. The objective of the proposed work is to develop a design and installation guideline for the rehabilitation of damaged composite pipes based on the damage class. For this purpose, damage characterization using SEM, CT Scan, Thermo-graphy imaging and other available techniques would be first studied and classify the damages in composite pipes under low velocity impact. Next, the methodology for the rehabilitation system would be investigated through available standards and codes to understand the state of the art and to identify the potential areas where existing methods can be improved. The main objective is to focus on the quality related issues during repair and post-repair quality assessment methods. The analysis of composite pipe rehabilitation is a complicated task. The codes usually provide some closed form formulae and only discrete values can be obtained. However a detailed study can be made by a numerical simulation through finite element analysis; nevertheless quality of the results would depend on the availability of actual material properties. An experimental study is therefore useful for validating the numerical results and to identify the practical quality issues and assess the quality of an actual repair. Effect of major parameters (such as surface preparation, composite layer thickness etc.) on the resulting performance of the composite repair can be investigated to formulate some guidelines related to design of the composite pipe rehabilitation system.