热应力作用下LNG储罐外罐裂缝及失效时间分析

Analysis of the fracture pattern and failure time of LNG outer tanks under the action of thermal load

对于大型液化天然气储罐,内罐泄漏时,由于内外表面温差产生的巨大热应力对于外罐裂缝开展及储罐失效有非常重要的影响。为了获得外罐裂缝的开展规律以及储罐失效时间以便指导实际工程的设计与维护,利用传热学与弹塑性力学相关理论,提出了一种应力叠加方法,近似计算在内罐泄漏时外罐出现裂缝的内外温差,并且结合数值模拟结果进行对比分析,验证理论方法的准确性,确定裂缝开展规律,最终求得内罐从最不利泄漏点开始泄漏到外罐内侧混凝土开裂的储罐失效时间。结果表明:①内罐泄漏时,热应力巨大,不可忽略,热应力和其他荷载共同作用导致外罐产生大量裂缝,裂缝首先在外罐顶部内表面产生,并迅速向外表面开展,最终贯穿罐顶,导致储罐失效;②首次求得了储罐从内罐开始泄漏到外罐产生裂缝的最小时间,在此时间内采取有力措施及时处理,对控制事故发展、避免发生严重灾害具有重要意义。

For large LNG storage tanks, when leakage occurs in the inner tank, the thermal stress due to the temperature difference between the inner and outer surfaces has a very significant effect on the cracks development and failure of the outer tank wall. In or- der to obtain cracks law and failure time of the external wall and further to guide the design and maintenance of the actual project, the heat transfer theory and elastic-plastic mechanics were used to propose a stress superposition method to approximately calculate the temperature difference of the outer tank when it cracks in the inner tank leakage state. And numerical simulation results were compared to verify the accuracy of the theoretical method, determine the law of crack development, and calculate the time from the leak of the most disadvantaged inner tank leak point to the concrete cracks of the outer tank. The results show that： ①in the inner tank leakage state, the temperature stress is enormous and cannot be ignored; cracks first appeared in the inner surface of the top of the tank wall, and quickly developed to the outer surface, and ultimately ran through the top of the tank wall, causing the tank fail- ure; ②obtaining the time from the inner tank leaking to the outer tank cracking for the first time and taking effective measures with- in the above time is of great significance to avoiding serious disasters.