Chemical composition:

Chemical composition and mechanical properties

The reason why 20G is capable of handling high-pressure environments is due to its balanced chemical composition and excellent mechanical properties.

Chemical composition (%):

Carbon (C): 0.17~0.23

Silicon (Si): 0.17~0.37

Manganese (Mn): 0.35~0.65

Phosphorus (P): ≤ 0.025

Sulfur (S): ≤ 0.015

Residual elements such as chromium (Cr), molybdenum (Mo), and nickel (Ni) are also strictly limited.

Features: The low-carbon design ensures good welding performance and processing plasticity, while the lower sulfur and phosphorus content improves the purity of the steel and enhances its resistance to high temperature creep.

Mechanical properties (taking GB 5310 as an example):

Tensile strength (σ b): ≥ 410 MPa

Yield strength (σ s): ≥ 245 MPa

Elongation rate (δ): ≥ 24%

Impact energy: There are corresponding requirements based on the size.

Characteristics: It has sufficient strength and a good combination of plasticity and toughness, and can effectively withstand internal high pressure and external loads.

Main features and advantages

Excellent high-temperature strength: At the working temperature of the boiler (usually ≤ 450 ° C), 20G can maintain high durability and creep resistance, and is not prone to plastic deformation and fracture.

Good antioxidant properties: Its surface can form a dense protective film in high-temperature water vapor, slowing down the rate of further oxidation and corrosion.

Excellent process performance: including good cold and hot processing performance such as cold bending, hot bending, and expansion, and more importantly, excellent welding performance, making it easy to install and manufacture on site.

High organizational stability: Under long-term high temperature and high pressure, the metallographic structure (ferrite+pearlite) is relatively stable and less prone to aging and performance degradation.

Main application areas

20G high-pressure boiler tubes are widely used in the following key areas:

Power plant boiler:

Water cooled wall: The vertical shaft pipes around the boiler furnace absorb radiant heat and are the main evaporative heating surface of the boiler.

Economizer: uses the heat from the exhaust gas at the tail of the boiler to preheat the feedwater, reduce the exhaust gas temperature, and improve efficiency.

Superheater: Heating saturated steam into superheated steam with a certain temperature.

Reheater: Heat the steam from the high-pressure cylinder of the steam turbine again and send it back to the intermediate pressure cylinder to continue working.

Connecting pipes: such as header connecting pipes, steam connecting pipes, etc.

Industrial boilers: Heating surface pipelines and piping systems of medium and high pressure boilers used in various industries such as petrochemicals, textiles, printing and dyeing, and papermaking.

Other fields: Can be used for pressure bearing components such as high-pressure vessels and heat exchanger equipment.

Production process flow

The requirements for producing 20G high-pressure boiler tubes are extremely strict, mainly using the production process of hot-rolled or cold drawn (rolled) seamless steel tubes:

Tube billet acceptance → heating → perforation → tube rolling → sizing → cooling → straightening → pipe cutting → non-destructive testing (100% inspection) → mechanical performance testing → metallographic examination → hydrostatic testing → surface inspection and length measurement weighing → painting and packaging.

Among them, non-destructive testing (usually ultrasonic or eddy current testing) and hydrostatic testing are key steps to ensure its pressure safety, ensuring that each steel pipe has no internal defects and can withstand more than 1.5 times the working pressure.