球罐裂纹及不同修复过程的残余应力

ANALYSIS OF CRACK AND RESIDUAL STRESS OF LIQUEFIED PETROLEUM GAS SPHERICAL TANK

壁厚为42mm的1 500m3液化石油气球罐,运行4年后出现大量裂纹,在局部补焊中又反复出现裂纹,最后采用了对赤道带大环焊缝的重新焊接及整圈热处理才使球罐得以修复。用X射线法对该球罐进行了系统的残余应力测试。结果表明,内壁赤道带原始焊缝处残余应力高达0.72sσ,说明球罐建造时的热处理效果较差;而局部修复及热处理后在焊缝附近残余应力接近或达到屈服应力,又表明局部热处理未起到应有作用。在球罐大环重新焊接及整圈热处理后的相同位置又进行两次测试,残余应力水平大幅度降低,整体下降约50%,显示最终的热处理效果良好。

There were a large number of cracks found in liquefied petroleum gas （LPG） spherical tank after servicing for four years, the wall thickness of the tank is 42mm, and the volume is 1 500m^3. Besides, cracks were repeatly found during local patch welding in the process of repairing, finally recovering the spherical tank by re- welding and heat treatment to the equatorial welded zone with half year. Residual stress was measured roundly by X- ray. The results show that the residual stress is as high as 0. 72as at the prior welded equatorial zone. It indicates that the result of heat treatment during producing is not very well. After local repairing and heat treatment, the residual stress reaches or approaches the yield stress. So the local heat treatment didn＇t make the potential result. Taking re-welding and heat treatment to the equatorial zone, and testing the same place for tow times, the residual stress reduce greatly, the average reduce reach about 50%, so the result of final heat treatment is better.