External surface crack growth in offshore steel pipes reinforced with CRS subjected to fatigue bending

Abstract

The Composite Repair System (CRS) is an advanced maintenance technique in the pipeline industry. In past a few decades, researchers applied composite materials to repair through-thickness cracks in pipes, which found that the CRS significantly decreased the crack growth rate. However, the investigation on repairing external surface cracked steel pipes is limited in open documents. Understanding the surface crack growth behaviour reinforced with Fibre-Reinforced Polymer (FRP) are of great importance. In this paper, we have experimentally studied the CRS reinforced external surface cracked steel pipes subjected to cyclic bending. In total, nine groups of 27 surface cracked pipes have been tested, containing three different sizes of the initial notch and four different CRS reinforcement schemes. The results show that the CRS has significantly decreased the crack growth rate and prolonged the residual fatigue life. Using more layers of CFRP can evidently facilitate the reinforcement effectiveness, while the surface crack growth is insensitive with the bond length. The inversely diagonal wrapping pattern performs less effective than the other reinforcement schemes. The experimental investigation in this paper is of instructive value to facilitate the further application of CRS in the offshore pipeline industry.