Zinc Smelting Cooling Pipe Failure Analysis And Countermeasures

Liquid Zinc cooling is one of very important steps in the course of melting Zinc by fire method. Cooling pipe made of 20 steel seamless tubing is widely used to cool liquid Zinc in Zinc smelting industry and its life is especially short that leads to consume of many cooling pipes. In this paper, the life of the cooling pipe of Zinc smelting is discussed in several parts as follows:The relevant thermal stress distribution graphs and regular patterns of the cooling pipe of Zinc smelting are obtained, with using the large-scale finite element analysis software ANSYS. The maximum thermal stress is 337MPa achieving 86% tensile strength of the cooling pipe and the site of the maximum thermal stress is the joint of bent section and linear section that it inclines to bent section. The effective factors such as current velocity and thickness and so on are discussed on the temperature field of the cooling pipe. The temperature of the cooling pipe on cold face is decreased and both the temperature gradient and the thermal stress are increased if the current velocity of the cooling water is increased, while the effect of thickness change of the cooling pipe is comprehensive.The reasons of producing residual stress lie in inhomogeneous plastic deformation and elastic deformation in plastic deformation process in theory. The residual stress is decreased using heat treatment. The data of residual stress are measured by using cut method and the peak value is 181MPa.There are the small surface tension and the strong osmosis and resistance of corrosion about liquid Zinc and it can form Fe-Zn alloy with steel of cooling pipe and can dissolve the C and the Si in cooling pipe. Liquid Zinc is not compatible with cooling pipe. Therefore, the compatibility is a decisive factor on the life of cooling pipe in liquid Zinc.The damage reason of the cooling pipe of Zinc smelting is high temperature corrosion and stress corrosion. Thermal stress plays an important role between the thermal stress and the residual stress to thedamaged site of the cooling pipe of Zinc smelting.The technique measures to improve life of the cooling pipe of Zinc smelting are to improve the corrosion resistance and to decrease thermal stress. The life of the cooling pipe of Zinc smelting is improved effectively by improving stuff such as using Fe-Al alloy and Fe-B alloy, surface treatment such as using surface coated material and surface boronisation treatment.