试论含焊接缺陷输油管的失效过程及其安全性

Discussion about Failure Stress and Failure Process of Welded Crude Oil Transmission Line Pipe

正常工艺生产的输油管（不含穿透性缺陷）具有足够的断裂韧性值，但在水压试验时，却全部发生了爆裂．分析表明破坏过程是管中非穿透缺陷由于周围材料流变而变成穿透裂纹，使管子失效，所以失效抗力仅取决于管材及焊缝强度．当穿透裂纹撕裂到临界尺寸时，管子爆裂才发生．仅在这时，断裂韧性和强度才对爆裂应力有影响．因为用在输送线上管子的初始缺陷是非穿透性的，所以提高材料强度减少焊缝缺陷是增加失效应力的有效措施．

The failure process for crude oil transmission line pipes produced under normal manufactureing conditions have enough fracture toughness. But all the pipes bursted under hydrostatic pressure testing. Analyses show that no penetrating defects in the pipe turn into penetraing crack, which results from the flow of the materials around the defects and causes the failure of the pipe. So failure stress depends only on the strength of the pipes and welding.Only when the penetrating crack tears to the critical length, the break up of the pipe takes place. Only in this condition, both the fracture toughness and strength of material have an effect on the break up stress. So the break up stress is related to both the fracture toughness and the strength of the pipes and welding. The initial defects in the pipes used in transmission line are of no penetrating, so an effective way for increasing the failure stress is to decrease the defects size and to increase the strength. The relationship curves between failure stress and crack size were given.