Abstract: It is very important to study the appearance defects and cause analysis of large diameter hot bending pipe for elbow quality control. The thermal processing defects of raw materials were mainly analyzed from the aspects of steel plate scab, steel plate surface inclusion, steel plate scratch and rub, steel plate folding, steel plate pockmarks and pockmarks, straight seam steel pipe weld defects. The causes of hot processing defects of the bending pipe were analyzed from the aspects of wave form on the arc side of the elbow袁and cracks or fracture on the outer arc side during the hot bending process, and collapse of the pipe end or arc section during the heat treatment process of elbow pipe.