Material of the boiler convection tube bank

According to the safety supervision regulations for steam boilers, steel pipes in accordance with GB5310 must be used.

Seamless steel tubes specified in GB5310-1999 \"Seamless Steel Tubes for High-Pressure Boilers\" can be used for manufacturing, in accordance with the technical requirements outlined in JB/T1611 \"Technical Conditions for Boiler Tubes\". This standard applies to fixed hot water boilers, as well as fixed steam boilers with a rated steam pressure not exceeding 13.7 MPa and a rated steam temperature not exceeding 540 degrees; it can also be used for subcritical pressure steam boilers.

In accordance with the provisions for boiler steel pipes in Table 3-2 of Article 23 of the \"Regulations on Safety Supervision of Steam Boilers,\" for convective tube bundles with a working pressure of 10 MPa, grade 20G as specified in standard GB5310-1995 \"Seamless Steel Tubes for High-Pressure Boilers\" can be used. In boilers, the term \"design pressure\" is not used; the pressures that are generally relevant include: rated pressure, calculated pressure, operating pressure, and for hot water boilers, the pressure at the boiler outlet.

Use pipes of type 5310 for strength calculations; as long as they meet the requirements, it is acceptable.

Without considering temperature, it’s not possible to determine this precisely. Generally speaking, when the pressure reaches 10 MPa, the steam temperature is around 540 degrees. Using 20G material is not suitable; alloy steel is generally required in such cases.

Yes, this issue of pipe restraint should be given due attention; when selecting materials, ones that meet higher standards to fulfill these requirements should be used, otherwise accidents caused by extremely high pressures leading to pipe rupture can be very problematic! !

140t/h, 9.8MPa boiler: the water wall, economizer, and desuperheater are made of 20G GB5310; the cyclone superheater and low-pressure superheater are made of 15CrMoVG； Screen superheater, high-temperature type 12CrMoVG

Thank you to everyone above! May I ask if two-way steel can be used?

The temperature is generally between 350 and 500 degrees; what material should be used? If the operating temperature is between 450 and 750 degrees, what material should be used?

With a vapor generation pressure of 10 Mpa, the saturated steam temperature should be around 330 degrees. Is it necessary to use alloy steel?

Lou, you gave a pressure-related piece of information; the pressure is related to choosing the thickness of the pipe. Based on the calculation using a saturated temperature of 330 degrees Celsius corresponding to 10 MPa, and considering that the temperature of the pipe wall is generally 20 degrees higher than that of the fluid, the temperature of the steel pipe is around 350 degrees. At this temperature, 20G is sufficient. The recommended operating temperature for 20G is below 450 degrees Celsius, with a maximum of up to 475 degrees Celsius. At even higher temperatures, alloy steel must be used; for example, the recommended operating temperature for 15CrMoG is below 510 degrees Celsius, with a maximum working temperature of up to 530 degrees Celsius. Choose the material based on temperature. This post was last edited by eddy-8280103 on 2009-3-19 10:31.]

Material specifications: Round steel WG1608-2004 -------------------------------------------------------------------------------- Steel grade, technical requirements, specifications Φmm: Q235-A GB700-88 – 6, 8, 10, 12, 14, 16, 18, 20, 25, 28, 30, 36; 20 GB/T699-99 – 14, 16, 20, 25, 28, 30, 36, 38, 40, 45, 50, 55, 60, 70, 75, 80, 90, 100, 120, 140, 160, 180, 200, 220, 250, 300, 350; 25 – 22, 30, 32, 40, 50, 60, 70, 80, 90, 100, 120; 35 – 12, 16, 18, 20, 25, 28, 36, 40, 45, 50, 55, 60, 70, 75, 80, 90, 100, 120, 160, 180, 300; 45 – 12, 16, 20, 25, 30, 35, 40, 45, 50, 55, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 180, 200, 240, 250, 300, 350. 12Cr1MoV GB/T3077-99 – 8, 12, 16, 18, 20, 25, 30, 36, 40, 45, 50, 55, 60, 70, 75, 80, 90, 100, 120, 140, 170, 220, 250, 300, 350; 15CrMo(A) – 28, 38, 42, 45; 25Cr2MoVA – 18, 26, 30, 40, 45, 50, 55, 60, 70, 80, 90, 100; 25Cr2Mo1VA – 20, 26, 30, 40, 45, 55, 90; 40Cr – 18, 20, 30, 40, 50, 65, 85, 100, 120, 150, 200; 30CrMoA – 26, 28, 30, 36, 40, 45, 50, 55, 60, 70, 75, 80, 85, 90, 100, 120, 140, 160, 220, 250, 280; 38CrMoA1A – 20, 28, 35, 40, 45, 50, 55, 60, 70, 80, 90, 100, 120, 150, 170; 1Cr13 GB1220-92 – 6, 12, 18, 20, 25, 30, 36, 40, 45, 50, 55, 60, 70, 80, 90, 120; 2Cr13 GB1220-92, GB1221-92 – 16, 20, 25, 30, 35, 40, 45, 50, 55, 60, 70, 80, 100, 120, 150, 250; 3Cr13 – 8, 10, 12, 20, 25, 30, 35, 40, 45, 50, 55, 60, 70, 80, 90, 100, 120, 150, 200; 1Cr18Ni9Ti – 10, 16, 20, 25, 30, 35, 40, 45, 50, 55, 60, 70, 80, 90, 100, 120, 150, 180, 200; 20Cr1Mo1V1 – as per agreement – 20, 28, 40, 60, 80, 100, 150; 1Cr20Ni14Si2 GB1221-92 – 12, 35, 80; SA675Gr70; ASME 210. Note: The types, specifications, and allowable tolerances for round steel are in accordance with GB702-1986. 　 --------------------------------------------------------------------------------

The key issue is that we really want to build a waste heat boiler with an operating temperature of around 650 degrees, potentially reaching up to 750 degrees, and a working pressure of 10.0 MPa. What type of tube material should be used?

The key is not to look at the external flue gas temperature, but rather the temperature of the medium inside the pipe. The medium flowing inside the pipe provides excellent cooling for it; generally, the operating temperature of a pipe with good flow and heat transfer is the temperature of the medium plus 20 degrees Celsius. For example, in your convective tube bundle, the temperature of the steam-water mixture at a saturation pressure of 10 MPa is 330 degrees Celsius; therefore, the temperature of your steel tubes is 350 degrees Celsius (there is no need to consider the temperature of the hot flue gases, as that temperature is used to calculate the heat transfer coefficient and the heat exchange area). So, you can use 20G material.

If the operating temperature reaches 650 degrees, Incoloy material could be considered; for our methane conversion furnace tubes, where the temperature at the outlet is 800 degrees, Incoloy 800 is used. It is a solution-strengthened nickel-based corrosion-resistant alloy, and it is a steel grade from the American company Haynes. This steel grade is a standard heat-resistant, corrosion-resistant, high-strength engineering material, commonly used in industrial furnaces, heat exchanger tubes, and other equipment that requires resistance to high temperatures. These steel grades are delivered after being subjected to solution treatment followed by pickling. This steel is very difficult to produce, which is why it is also expensive. Using it in its hot-rolled state represents a huge waste; if such a product is used in that form, it is likely to be fake.

Answer to the question on floor 9: Duplex stainless steel possesses high impact toughness at room temperature, but when it is exposed to temperatures above 300°C for an extended period of time, its microstructure changes, which leads to a decrease in impact toughness. Therefore, relevant foreign standards for pressure vessels specify 250–280°C as its maximum operating temperature. Additionally, –50°C is the low-temperature brittle transition temperature for duplex stainless steel; thus, without taking medium factors into account, the appropriate operating temperature range for duplex stainless steel is –40–250°C. If medium factors are considered, the appropriate operating temperature range becomes even narrower.

Duplex stainless steel is primarily used in environments with high corrosion levels, such as urea plants and nitric acid plants; it is not suitable for use in high-temperature environments. Stainless steels for high temperatures: 304H, 316H, A321, A347, HK40, Incoloy800, etc.

In the ammonia synthesis plant, the first waste heat boiler features a process gas temperature of 950°C in the tube side, with T11 material used; the boiler water temperature on the shell side is 340°C, using 20# material, and the thin tube sheet is equipped with a fire-resistant casting layer. The material selection is directly related to the operating conditions, such as temperature, pressure, and the properties of the medium (whether it contains solid particles, whether there is a tendency for stress corrosion, etc.).

20G/ 12CrMoG/ 15CrMoG/ 12Cr1MoVG/ 12Cr2MoWVTiB/ 12Cr3MoVSiTiB

20G is used, and the applicable standard is GB5310-1999 \"Seamless Steel Tubes for High-Pressure Boilers\"