Cracking causes of heat exchanger tube of circulating oil steam generator

Cracking occurred at the middle expansion part of the outermost heat exchange tube on the upper part of the circulating oil steam generator of a company. The reasons for the cracking of the heat exchange tube were analyzed by means of macroscopic observation, analysis of scale composition, metallographic examination, hardness test and scanning electron microscope analysis. The results show that the cracking of the heat exchange tube was mainly caused by alkali stress corrosion. Alkali embrittlement cracks had been formed on the outer wall of the heat exchange tube before the fracture. Under the axial tensile stress, the alkali embrittlement cracks expanded rapidly, and finally led to the cracking of the heat exchange tube.