Loading Capacities of Bonded Composite Pipe Joints of Different Structures

Fiber-reinforced composite materials are increasingly used in oil and gas transmission, and joints are the areas prone to failure in pipelines. Damage evolution in the adhesive joints connecting pipes made for basalt-fiber-reinforced polymers (BFRPs) was analyzed. First, finite-element models for three types of adhesive joints (single-lap, sleeve, and scarf ones) were developed. Second, an optimal cohesive zone model (CZM) for the adhesive layer was developed based on the inverse analysis of the results of debonding experiments. Finally, the damage evolution in the adhesive joints was analyzed under internal pressure, tension, bending, and torque, and their pipeline loading capacities were evaluated. Results showed that the single-lap joint exhibited the highest ultimate load-carrying capacity at a unit overlapping length, followed by the sleeve joint, but the scarf joint had the lowest unit ultimate load. For sleeve and scarf joints, the presence of a gap or a weak interface between two pipe adherends led to a reduction in their load-carrying capacity. These findings provide a basis for the design of the composite pipe joints.