在停车检验期间某混烃球罐下极带环焊缝处存在大量表面裂纹，采用X射线应力测定仪对裂纹集中部位的残余应力进行测试，并通过化学成分分析、力学性能测试、断口微观形貌观察等方法对球罐开裂的原因进行了分析。结果表明：球罐下极带环焊缝熔合线和热影响区处发生了硫化物应力腐蚀开裂；在腐蚀介质及较大的残余拉应力作用下，裂纹在残余拉应力最大的下极带环焊缝热影响区萌生，随后以穿晶和沿晶形式扩展至熔合线。焊接前应合理选材，选择适合的焊接和热处理工艺，提高球罐安装后去应力热处理的质量，以降低残余拉应力；焊接后通过隔绝腐蚀介质、除去介质中硫化氢或水的方法降低开裂敏感性。

During the inspection of a hydrocarbon mixing spherical tank, a large number of surface cracks were found at the lower plate girth weld position. The residual stress at the crack concentration position was tested by X-ray stress tester, and the cause of cracking of the spherical tank was analyzed by chemical composition analysis, mechanical property test and fracture micromorphology observation. The results show that the sulfide stress corrosion cracking occurred at the fusion line and heat affected zone in the lower plate girth weld of the spherical tank. Under the action of corrosive medium and large residual tension stress, the cracks initiated in the heat affected zone of the lower plate girth weld with the largest residual tension stress, and then propagated to the fusion line in the transgranular and intergranular forms. Reasonably selecting materials before welding, selecting suitable welding and heat treatment technology and improving the quality of stress relief heat treatment after spherical tank installation should be taken to reduce the residual stress; isolating corrosive media and removing hydrogen sulfide or water from the media were used to reduce the sensitivity of cracking.