Abstract: The internal pipeline components of a certain type tactical vehicle cracked during service. The cracking causes of the internal pipeline components were analyzed by means of macro observation, macroscopical examination, chemical composition analysis, tensile test, metallographic examination and micro analysis. The results show that the cover plate not welded in the thickness direction was the main cause for cracking failure of the pipeline components. The introduction of oxygen, sulfur and other typical corrosive elements in coolant was the secondary cause of cracking failure of the pipeline components. Under the combined action of stress and corrosive medium, the pipeline components cracked and failed.