Abstract: Causes of leakage from cylinders of high-pressure separators of Yuanrun Company in Henan oilfield are analyzed. It is found that all the leakage occur at the commissures on cylinders and are caused by weld defects. Welding residual stress and some specific corrosive medium also contribute to the failure of weld beads. This paper presents several specific remedy measures and some proposals concerning quality control during manufacture of high-pressure containers.