Application of CFRP Wrap for Reinforcing Undamaged Thin-Walled Pipe Bends under Thermal Expansion Loads

Abstract

Thermal stress analysis is an integral part of the design and integrity assessment of buried pipelines. Pipe bends can be subjected to significant cross-sectional deformations due to bending moments induced by thermal cycles, compared to straight pipes, and therefore are the most crucial component of the pipeline’s structural integrity. Fatigue fracture, which is the primary failure mode in pipelines under the thermal cycle, may occur at the crown region of the pipe bend in the form of a longitudinal crack. This specific failure pattern is primarily the result of excessive circumferential stress that may develop in the crown region of a pipe bend. The present paper suggests a novel approach to reduce the stress range at the crown region of pipe bends using carbon fiber-reinforced polymer (CFRP) wraps. This approach has been used in the pipeline industry to reinforce and repair corroded pipes. However, a very limited study on the use of CFRP wrap to enhance the mechanical behavior of undamaged pipe bends is available in the literature. This study employs an advanced finite element (FE) method to investigate the performance of buried pipe bends reinforced with CFRP composite wraps and subjected to thermal expansion-induced bending moment. A combined beam and shell-based FE model has been used in this study to ensure reasonable accuracy and remarkable computational efficiency for engineering practice. The FE results show that a 6 mm CFRP wrap around the pipe bend can decrease the von-Mises stress imposed by thermal expansion by up to 27.4%. In short, reinforcing pipe bends with CFRP wrap has a strong potential to decrease the stress range imposed in the pipe bend under thermal expansion-induced moments and consequently prevent fatigue failure in pipe bends.