Abstract: The gas collecting tube of hydrogen production plant of a company cracked in service. The causes of cracking on gas collecting tube were analyzed by means of chemical composition analysis, metallographic examination, fracture analysis and stress calculation. The results show that the over temperature operation of gas collecting tube resulted in the precipitation of chromium rich carbides at the grain boundary and the sensitization of gas collecting tube tissue, and the stress on the wall of the tube was much higher than the allowable stress, which led to the cracking of the tube wall in the stress concentration area preferentially and presented intergranular cracking.