Abstract: A heat-transfer oil pipe of a company fractured during use. The methods of macroscopic observation, chemical composition analysis, metallographic inspection, hardness testing and fracture analysis were used to analyze fracture reasons of the heat-transfer oil pipe. The results show that:the heat-transfer oil pipe was repaired by liquid iron containing high carbon, and it increased the brittleness of the material; under the exogenic action, the heat transfer pipe cracked at the position of the thin wall, which led to the heat-transfer oil leak; under the action of the heat-transfer oil pressure, the heat-transfer oil pipe cracked along the cross section.