[Weekly Topic] What are the requirements for boiler materials under critical conditions? (5.7--5.14)
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This post was last edited by zgj2405 on 2011-5-7 at 20:55. Any experienced professionals who have knowledge and practical experience with critical boilers please help me answer my questions. Thank you! ! !
Reply to 1# yingyonghuaxue9: For the heating surfaces in the high-temperature section of supercritical pressure boilers, austenitic steel grades must be used. Such steels not only need to possess high-temperature strength properties but also excellent resistance to high-temperature oxidation.
At the critical state, the temperature of water is only 374°C; as long as the temperature required for the material is higher than this value, there should be no problems. Therefore, there shouldn’t be any issues with the materials used. Generally, 15CrMoG and SA-213T12 are sufficient, and these are indeed the materials commonly used for the water walls of supercritical boilers. However, due to the high heat transfer in the furnace, in order to ensure that the water wall has sufficient cooling capacity, internal threaded tubes are generally used in areas with high thermal loads to guarantee the cooling of the water wall.
The critical temperature of water vapor is 374°C, while the heat resistance of 15CrMoG and 12CrMoV allows them to withstand temperatures up to 550°C. These materials are therefore the most commonly used piping materials for feedwater and steam in high-pressure boilers (critical boilers, supercritical boilers).
The range of steel pipes used in power plant boilers is as follows: for low-pressure boilers with temperatures below 450 degrees, high-quality carbon steels such as 10# and 20# are primarily used. Apart from 20A carbon steel, the steel tubes used for the water wall and economizer in medium and high-pressure units are mostly alloy steel tubes (such as 15CrMo, 12Cr1MoV, 102 steel, etc.). Additionally, boiler pipes can be made of low-alloy heat-resistant steel, martensitic heat-resistant steel, and austenitic heat-resistant steel.
What are the requirements for the material of superheated steam pipes under those critical conditions?
Reply to 2# linweihua6: Not bad, not bad
At the critical state, water has a temperature of 374°C and a pressure of 22 MPa. As long as the allowable temperature of the material is higher than this value, and the wall thickness is sufficient to ensure the required strength under such pressure and temperature conditions, there should be no problems. However, in supercritical boilers, there is an issue of excessively high wall temperatures in the water wall due to boiling heat transfer; therefore, internal threaded tubes are used in areas with high thermal loads to ensure that the water wall receives adequate cooling.
That’s great! I need to learn more*. At the critical point, water has a temperature of 374°C and a pressure of 22 MPa