In the past 10 years, the welding technology of boilers, pressure vessels and pipelines at home and abroad has made remarkable new developments. With the substantial improvement of boiler, pressure vessel and pipeline working parameters and the continuous expansion of application fields, there is an increasing demand for welding technology. The welding method, welding process, welding materials and welding equipment selected should first ensure the high quality of the welded joints, and must meet the requirements of high efficiency, low consumption and low pollution. Therefore, in this field, welding workers are always faced with complex and arduous technical problems, and they are constantly seeking the best solution. Through unremitting efforts, we have made major breakthroughs in many key technologies, and have been successfully applied in actual production, and have achieved considerable economic benefits, bringing the welding technology of boilers, pressure vessels and pipelines to a new level of development. New developments in boiler pressure vessels and steel for pipelines 1 New development of boiler steel Among the three types of steels for boilers, pressure vessels and pipelines, boiler steel is the fastest growing. This is mainly because in the past 10 years, the supply of fuel for coal-fired power stations has become increasingly tight, and reducing fuel consumption has become a worldwide urgent need. To this end, the efficiency of the boiler must be increased. Typically, for every 5% increase in boiler efficiency, fuel consumption can be reduced by 15%. The efficiency of the boiler is basically dependent on its operating parameters - steam pressure and steam temperature. Recently, the steam pressure of the 600~670MW supercritical boiler produced by the Shanghai Boiler Plant is 254bar, the superheated steam temperature is 569°C, and the thermal efficiency of the boiler is about 43%. If the boiler's operating parameters are increased to a very supercritical level, ie a steam pressure of 280 bar and a steam temperature of 620 ° C, the thermal efficiency of the boiler can be increased to 47%. At present, the highest working parameters of the world's supercritical boilers are 350bar/700°C/720°C, and the thermal efficiency of the boiler reaches 50%. It should be emphasized here that as the efficiency of the boiler increases, the emissions of SO2, NOX and CO2 in the boiler flue gas gradually decrease. Therefore, from the perspective of reducing air pollution, it is an inevitable development trend to design and manufacture special supercritical boilers with high working parameters. The increase in boiler steam parameters directly affects the strength properties of the pressurized parts of the boiler. Under supercritical and ultra-supercritical operating conditions, the main components of the boiler, such as membrane water wall, superheater, reheater, high pressure outlet header and main steam pipeline, have reached the creep temperature range of the steel. The steels from which these parts are produced shall have high corrosion resistance and oxidation resistance as well as good weldability and formability in addition to sufficient creep strength (or 105 h high temperature endurance) at specified operating temperatures. From the development stage of the steel for the main components of the boiler, even the water-cooled wall parts with relatively low working temperature must use Cr-Mo steel with more than 2% chromium or multi-component CrMoVTiB steel. According to current boiler manufacturing regulations, such low alloy steels must be heat treated after welding when the wall thickness exceeds the specified limits. Since the shape of the membrane type water wall is quite large, the length of the workpiece generally exceeds 30 m, and the post-weld heat treatment not only prolongs the production cycle, but also greatly increases the manufacturing cost. In order to solve this problem, a new steel grade 7CrMoVTiB1010 dedicated to membrane water wall was developed abroad. Recently, the steel grade has been approved by the American ASME and has been included in the US ASME material standard, the steel number is A213-T24. This steel is characterized by a carbon content of less than 0.10% and a sulfur content of not more than 0.010%, so that it has a fairly good weldability. No preheating is required before welding. When the wall thickness is not more than 10 mm, it may not be heat treated after welding. Under the supercritical steam parameters, when the vapor temperature reaches 700 ° C and the vapor pressure exceeds 370 bar, the wall temperature of the water wall may exceed 600 ° C. Under these conditions, 9%Cr or 12%Cr martensitic heat resistant steel must be used. These steel grades impose strict requirements on the welding process and post-weld heat treatment, and special process measures must be taken to ensure the joint quality of the joint. For boiler superheaters and reheater high temperature components, the operating temperature range is 560~650 °C under supercritical and ultra-supercritical steam parameters. In the low temperature section, 9~12% Cr steel is usually used. From the viewpoint of high temperature corrosion resistance, 12% Cr steel is preferred. In the high temperature range above 600 °C, austenitic chrome-nickel high-alloy heat-resistant steel must be used. According to recent research results, for high temperature superheater and reheater pipe fittings, in order to ensure high high temperature corrosion resistance and oxidation resistance, austenitic steel with chromium content greater than 20% should be selected, such as 25Cr-20NiNbN (HR3C) ), 23Cr-18NiCuWNbN (SAVE25), 22Cr-15NiNbN (Tempaloy A-3), and 20Cr-25NiMoNbTi (NF709). GUANGZHOU SUNPLUS TECHNOLOGY CO.,LTD , https://www.sunplussandpaper.com
In view of the many important industrial sectors involved in boilers, pressure vessels and pipelines, including firepower, hydropower, wind power, nuclear power generation equipment, petrochemical plants, coal liquefaction plants, oil transportation, gas pipelines, beverages, dairy processing equipment, pharmaceutical machinery The contents of welding technology are quite extensive in drinking water treatment equipment and liquefied gas storage and transportation equipment. Due to space limitations, this paper only introduces the following new developments in boilers, pressure vessels and pipeline steels, advanced welding methods and mechanization and automation of welding processes.