Fatigue Failure Analyses of Three Gas Cylinders of Long-Tube Trailers

Three cylinders of a long-tube trailer leaked during an inspection and typical quality test. Thus, failure analysis was performed to determine the cause of failure. Macroscopic observation, metallographic analysis, and fracture analysis were implemented. Cylinder 1 was found leaking during the inspection. The crack was from the inner to the outer surface of the wall, and stripes from tool marks were found on the inner surface. Metallographic analysis proved that the fatigue crack originated from the tool marks in cylinder 1. Cylinders 2 and 3, which are fiber-reinforced, failed during the typical quality test, with life of approximately 13,000 cycles. The inner surface of cylinder 2 had many folds, and the fatigue crack intensified from these folds. The folds were formed by the shot blasting treatment of the cylinder. The crack of cylinder 3 was found in the position of the cylinder bottle shoulder. The inclusion on the cylinder shoulder was observed, and that on the subsurface could move to the inner surface during the hot spinning process and propagate gradually under cyclic load. The three fatigue failure analyses showed that quality examination is important during the process of cylinder production.