Boiler Header Corrosion Fatigue Cracking Analysis

Boiler is widely used in various fields of industrial production of special equipment, due to the high parameters of the boiler can bring high energy conversion efficiency, so more and more of the boilers are required at high temperature and high pressure environment to run. Long run in this environment, not entirely without risk, as equipment corrosion and fatigue, will significantly reduce the device's safety and reliability. Its security is related to people's lives and property of the boiler to avoid accidents is the premise of normal use. This article was BG35-54-M medium plays high-pressure boiler header to the outer surface of ring mechanism of cracks on the boiler design, manufacture and operation of a certain theoretical significance and practical value.This article find from the actual work of crack body of Boiler Header start on the thick wall cylinder tube header name and temperature stresses were elastic mechanics analysis method was calculated, in Elasticity The method of calculation of thermal stress, respectively, and the internal pressure refrigerant then superimposed. And in accordance with the boiler operation and shutdown of the cycle, analyze the frequency of tension and compression stress cycle, should belong to the scope of low cycle fatigue stress.On the failure of components for the chemical composition and microstructure analysis ruled out the header material deterioration in the crack of the electron microscope, in the internal and edge cracks found containing Al, S, Cl, O, Na and other elements of the corrosion products, by corrosion product analysis and collection boxes cylinder operating environment, we concluded that S, O is a major factor in corrosion.We used electron microscope and metallographic to analysis cracks'shape. The crack extended from the surface to the depth of the side of the morphology and the literature that the crack than the latter belongs to the scope of the fatigue crack, but also has a special type, the crack tip along the grain, crack section with shell ridge.Finally, stress analysis, crack analysis, corrosion analysis, conclusion, our microscopic point of view from the material, combined with metallographic and electron microscope images, made between micro-corrosion and promote the mechanism of fatigue, stress corrosion caused by the surface concentration become the starting point of the crack, the crack advances in process, the cyclic stress level resulted in loss of corrosion products, guaranteed rot caused by the proliferation of channels of material, due to the crack tip phase difference between the organization and grain, but also to promote the crack tip plastic strain differences and further corrosion.Finally the conclusion is: Boiler Header's crack is corrosion fatigue crack.