Abstract: To find out the leakage cause for the serpentinetube elbow(SA-210C steel) in a supercritical boiler economizer, macroscopic morphology observation, chemical component analysis, stress calculation, mechanical property test, and metallographic observation were implemented on the elbow samples.The results show that the chemical composition of SA-210C, tensile properties at room temperature and hardness of straight pipe met the requirements of relevant standards. There was no obvious abnormality in metallographic structure,but the hardness at cracking part was much higher than the upper limit, and the plasticity and toughness were significantly reduced. Since the tube wall pitted by the crushing of foreign material could not meet the designing requirement,there were microcracks at the bottom of the pit because of stress concentration. Under the action of pressure of medium and thermal stress during operation, the microcracks rapidly expanded and caused brittle cracking.

Key words: tube of economizer, serpentinetube elbow, SA-210C steel, pit, hardness, plasticity, toughness, brittle cracking