20G: GB5310-95 acceptance standard steel (foreign corresponding grade: Germany’s ST45.8, Japan’s STB42, the United States SA106B), is the most commonly used boiler steel pipe, chemical composition and mechanical properties and 20 plate is basically the same. The steel has a certain strength at room temperature and medium high temperature, low carbon content, better plasticity and toughness, its hot and cold forming and welding performance is good. It is mainly used in the manufacture of high pressure and higher parameters of boiler fittings, low temperature section superheater, reheater, economizer and water wall, etc. Such as small diameter pipe wall temperature ≤500℃ heating surface pipe, and water wall pipe, economizer tube, large diameter pipe wall temperature ≤450℃ steam pipeline, collection box (economizer, water wall, low temperature superheater and reheater coupling box), medium temperature ≤450℃ pipeline accessories. Because carbon steel will produce graphitization in the long-term operation above 450℃, so the long-term maximum service temperature of the heating surface pipe is best limited to below 450℃. The steel in this temperature range, its strength can meet the requirements of superheater and steam pipeline, and has good oxidation resistance, plasticity, toughness, welding properties and other cold and hot processing properties are very good, widely used. The parts of the steel used in the Iranian furnace (referring to a single set) are the water inlet pipe (28 tons), the water inlet pipe (20 tons), the steam connection pipe (26 tons), the economizer container (8 tons), and the water reducing system (5 tons), and the rest are used as flat steel and derrick materials (about 86 tons).

Sa-210c (25MnG) : Steel number in ASME SA-210 standard. It is a small diameter tube of carbon manganese steel for boilers and superheaters, and a hot strength steel with pearl shape. In 1995, it was transplanted to GB5310 and named 25MnG. Its chemical composition is simple, except for the higher carbon and manganese content, the rest is similar to 20G, so the yield strength is about 20% higher than 20G, and the plastic and toughness are similar to 20G. The production process of the steel is simple and its cold and hot working performance is good. Using it instead of 20G, can reduce the thickness of the wall, reduce the amount of materials, but also can improve the heat transfer of the boiler. Its use parts and use temperature is basically the same as 20G, mainly used for working temperature below 500℃ water wall, economizer, low temperature superheater and other components.
Sa-106c: It is a steel number in ASME SA-106 standard. It is a carbon-manganese steel tube for high-temperature large-diameter boilers and superheaters. Its chemical composition is simple, similar to 20G carbon steel, but the content of carbon and manganese is higher, so its yield strength is about 12% higher than 20G, and the plastic, toughness is not bad. The production process of the steel is simple and its cold and hot working performance is good. Using it instead of 20G manufacturing collector (economizer, water cooling wall, low temperature superheater and reheater coupling box), the wall thickness can be reduced by about 10%, which can not only save the material cost, but also reduce the welding workload, and improve the stress difference when the coupling box starts.
15Mo3 (15MoG) : It is a steel pipe in DIN17175 standard. It is a small diameter carbon molybdenum steel tube for boiler and superheater, and a pearlescent type hot strength steel. In 1995, it was transplanted to GB5310 and named 15MoG. Its chemical composition is simple, but it contains molybdenum, so it has better thermal strength than carbon steel while maintaining the same process performance as carbon steel. Because of its good performance, cheap price, has been widely used in the world. However, the steel has a tendency to graphitization after long-term operation at high temperature, so its operating temperature should be controlled below 510℃, and the amount of Al added in smelting should be limited to control and delay the graphitization process. This steel tube is mainly used for low temperature superheater and low temperature reheater. The wall temperature is below 510℃. Its chemical composition C0.12-0.20, SI0.10-0.35, MN0.40-0.80, S≤0.035, P≤0.035, MO0.25-0.35; The normal strength level σs≥270-285, σb≥450-600 MPa; Plastic delta 22 or higher.