Materials for high temperature boilers (marketing department of Shanghai HY Industry Co., Ltd)
In order to meet the development needs of ultra-supercritical units, boiler steel has undergone a series of changes. Especially when the secondary reheat unit is put into production and operation, the main reheat steam temperature and pressure increase, and the conventional boiler steel used in the early stage can no longer meet the actual demand, and cannot effectively guarantee the safe and stable operation of the unit. This paper mainly introduces several Materials for high temperature boilers that have been applied to ultra-supercritical units.
Boiler steel has developed from early carbon steel, carbon-manganese steel (such as: 20G, 106C, etc.) Type T91, T92, T122, etc.) and new austenitic alloy steels (such as: TP347HFG, super304H, HR3C, NF709, etc.), and even 700 ℃ nickel-based alloy steels that have not yet been put into operation (such as: Inconel617, Inconel740, etc.) , has formed a complete boiler steel system, which basically meets the needs of different grades of boiler steel from low parameters to large capacity and high parameters. The new steel grades are basically developed on the basis of T91, TP304H, TP347H, and TP310H by refining grains or adding strengthening elements such as W, Cu, B, and Nb. The comprehensive performance is more superior, and it is more suitable for high-parameter units. Pressure and temperature requirements, and can reduce the cost of steel.
When selecting the Materials for high temperature boilers tube, in terms of technology, the following factors should be considered comprehensively: one is high temperature creep performance, the other is flue gas corrosion resistance, and the third is steam oxidation resistance. In addition, processing performance, welding performance, mechanical performance, material cost and operability during mass acceptance should be considered comprehensively. The metal temperature of the heating surface tube in the furnace is about 25°C-38°C higher than the steam temperature, and the maximum wall temperature of the metal is the limit temperature it can withstand. The difference between metal temperature and steam temperature should be fully considered, and reasonable materials should be selected according to actual operating conditions.
T92 steel is on the basis of T91 steel, the content of Mo element is appropriately reduced, a certain amount of W is added, and a small amount of B is added in a controlled manner. Through alloying improvement, T92 steel is compared with other 9Cr series heat-resistant steels. , the high temperature corrosion resistance and oxidation resistance have not improved much, but the high temperature creep strength has been greatly improved. T92 steel has been applied to the superheater tube panel of the partition panel, and the metal wall temperature of the application section should not exceed 650°C. P92 steel is widely used in the main steam pipes of ultra-supercritical units, large-diameter pipes such as primary reheating and secondary reheating.
Super304H is an austenitic stainless heat-strength steel. On the basis of TP304H, cheap Cu, Nb, and N are added to organize the growth of austenite grains and obtain a smaller grain size. The dispersion strengthening of Cu-rich phase particles greatly improves the high temperature creep strength of Super304H. Super304H has a very high cold deformation ability and stable welding process performance. It has been applied to the inlet section of the inner ring of the tube panel of the final stage reheater and the outlet section of the rear panel superheater. The metal wall temperature cannot exceed 700°C.
TP347HFG is developed on the basis of TP347H through the precipitation of NbC to achieve grain refinement. Its high temperature steam corrosion resistance and creep rupture strength are improved compared with TP347H. It has been applied to the inlet section of the rear panel superheater and the inlet section of the front panel of the high temperature reheater, and the metal wall temperature cannot exceed 650°C. However, since TP347HFG and TP347H are not very different in terms of element content, they cannot be tested by spectral analysis in the mass acceptance stage, but can only be distinguished by the grain size of the metallographic structure, which greatly increases the workload of acceptance.
HR3C is developed on the basis of TP310H by adding N and Nb elements. Creep rupture strength is enhanced by the precipitation of fine and stable nitrides during aging. Its anti-steam oxidation performance is the most prominent among the applied steel grades. It has been applied to the outlet section of the tube panel of the final superheater and high temperature and high pressure reheater, and the metal wall temperature should not exceed 700°C.
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