Two 45-degree elbows can not be welded into a 90-degree elbow

　　Two 45-degree elbows can not be welded into a 90-degree elbow for use because the elbow is a concentrated area of stress on the pipe, and most of the stresses of expansion and cooling deformation are released at the elbow. In addition the weld itself should be weak links, fatigue deformation will soon lead to cracking damage, which buried a lot of hidden dangers, so do not figure a moment convenient, and ultimately cause huge losses.