SA213-TP347H stainless steel original manufacturing process make the steel with big grain size , the grain size of G.S No4-5 level. The coarse grain TP347H stainless steel is used in the boiler superheater and reheater components, and in the case of high temperature operation, the oxide formed by the oxidation of the inner wall of the tube is easily peeled off. The oxide is deposited at the elbow of the pipe, causing the tube to overheat or even explode. What is more serious is that the exfoliation of the scale into the gas turbine will cause serious corrosion damage to the gas turbine. Studies have shown that the prevention of austenitic stainless steel tube surface corrosion of an effective measure is to reduce the grain size, fine grain of austenite structure can accelerate the diffusion of chromium in the grain boundary migration and formation of a layer of oxygen in the steam Dense chromium-rich chromium oxide (Cr2O3), this chromium-rich oxide layer can prevent high temperature steam on the tube wall further oxidation. In order to improve the high temperature strength of austenitic stainless steel, it is necessary to increase the melting temperature. However, to improve the melting temperature will lead to greater grain size, in order to solve the high temperature strength and grain larger contradiction, Sumitomo company through the improvement of TP347H manufacturing process, access to high temperature strength fine fine grain TP347H. The difference between the fine grain process and the coarse grain process is that the new process conducts the softening annealing of the tube at a temperature higher than the final solidification temperature before the last extubation. The precipitation of a large number of Nbc particles during the high temperature softening annealing hinders the obstruction of the austenite grain growth during the final solidification process. The grain size of the fine grain of TP347H stainless steel is G.S No8. Ie SA213-TP347HFG.
In order to further improve the high temperature creep strength, high temperature corrosion resistance and steam oxidation resistance of stainless steel tubes for boiler, Japan has invested a lot of manpower, material and financial resources. For the existing SA213-TP304H, SA213-TP347H, SA213-TP310H three (TP347HFG), HR3C (TP310HCbN) three kinds of new stainless steel. It is a new type of stainless steel with super-supercritical boiler with stainless steel.
