The purpose of the paper is to present the role of the internal reinforcing on the structural integrity of steel pipes, based on numerical and experimental investigations. For FE analysis of unreinforced case three mechanical models were applied: multilayered elastic shell, 3D elastic solid and 3D elastic-plastic solid FE models. The aim of the numerical analysis was to clarify deformations, stresses and strains in the surrounding area of defects both in the steel pipe and on the composite reinforcement. A further task is to determine numerically the width of reinforcement and the number of layers needed for the repair. For experimental investiga-Tions internal reinforcement was developed using glass fibre polymer matrix composite. Fa-Tigue and burst tests were performed on pipe sections containing artificial metal loss defects. Both unreinforced and reinforced pipeline sections were examined. The applicability of the hybrid structure was demonstrated by means of the numerical and the experimental results.

The lifetime management of different engineering structures and structural elements is one of the important technical-economic problems nowadays. The purpose of the paper is to present the role of the external reinforcing on the structural integrity of industrial and transporting steel pipelines, based on experimental and numerical investigations. External reinforcement was developed using carbon fibre polymer matrix composite (PMC). Fatigue and burst tests were performed on pipeline sections containing natural and artificial metal loss defects, and girth welds including weld defects (passed and not passed quality). Both unreinforced and reinforced pipeline sections were examined. For the FEM investigation of the problem three groups of mechanical models are applied: multilayered elastic shell, 3D elastic solid and 3D elastic-plastic solid FEM models. The aim of this numerical analysis is to clarify the deformation, stresses and strains in the surrounding area of defects both in the steel pipe and in the composite reinforcement. A further task is to determine numerically the width of the reinforcement and the number of layers needed for reinforcement or repair. The applicability of the hybrid structure (steel + PMC) was demonstrated by means of the experimental and the numerical results. © 2010 Published by Elsevier Ltd.