Fundamental Study on the Application of Laser Peening for Residual Stress Improvement in Marine High-Pressure Fuel Pipes

In marine engines, high-pressure fuel pipes are subjected to extremely high pressures exceeding 1000 bar, which results in fuel injection. Due to the high operating pressure inside the pipes, the stresses acting on them are increased, making the pipes prone to failure. To reduce the stresses imposed on the high-pressure pipes, residual stresses are introduced through pre-stressing processes tailored to the operating pressure. However, in the bent sections of the pipes, some residual tensile stresses from the bending process remain, potentially leading to cracks. Therefore, this study applied laser peening to assess its effectiveness in improving the residual stresses of marine high-pressure fuel pipes. Initially, basic experiments were conducted by applying laser peening to SCM440 plates, which are the main material for marine high-pressure fuel pipes, to understand the effects of laser peening. It was found that changes in the laser beam overlap rate had a greater impact on residual stress reduction than increases in laser output. Subsequently, laser peening was performed on the bent sections of actual high-pressure fuel pipes, and it was confirmed that the residual tensile stresses present inside the pipes were improved with increasing laser beam overlap rate.