LEAK-BEFORE-BREAK ANALYSIS ON HIGH-TEMPERATURE AND HIGH-PRESSURE PIPELINES OF MARINE POWER PLANT

The leak-before-break (LBB) method is applied to the safety assessment of high-temperature/high-pressure pipelines in a marine power system. The characteristics of the pipe loads induced by underwater impact, swing and variation of temperature/pressure are discussed. The fatigue stress spectrum is analyzed for typical π-shaped pipe. Then the fatigue propagation characteristics of a surface crack is predicted based on the fracture mechanics and finite element method to ensure that no leak occur when the pipe is on service. The critical length of a through-wall crack is calculated by the J integral-tearing modulus approach, and then compared with the minimum detectable leakage crack length for the purpose that unstable fracture would not be happened before the leakage is detected. One could draw a conclusion that the effect of swing-induced alternation stress with small stress amplitude should not be neglected, due to its high cycle times. And the maximum stress occurs when the cracked pipe bears underwater impact, which may probably lead to unstable fracture.