船舶动力装置高温高压管道破前漏分析

将破前漏（LBB）方法运用于船舶动力装置高温高压管道的安全分析。探讨由于水下冲击、摇摆、温度和内压变化引起的管道载荷特性。以典型π型管道为研究对象，统计出疲劳应力谱。基于断裂力学理论和有限元方法，预测管道表面裂纹疲劳扩展行为，确保管道在运行期间不发生泄漏。采用J积分撕裂模量汇交法计算管道穿透裂纹的临界裂纹尺寸，并与最小可监测裂纹尺寸比较，确保即使发生泄漏，也有足够的安全余量在裂纹被发现前不发生失稳断裂。研究表明：尽管摇摆产生的管道交变应力幅较小，但循环次数高，对裂纹扩展的影响不可忽略；在水下冲击载荷作用下，管道承受最大应力，最有可能导致裂纹失稳扩展。

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.