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Impact of Normalizing Temperature on High-Strength Bainitic Steel Pipe

Understanding the influence of normalizing temperature on the microstructure and properties of high-strength bainitic steel pipe is crucial for optimizing its performance in various applications. In this...

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High Pressure Boiler Tubes

Posted: 02/19/2021 16:19:56 Hits: 30

Features of high pressure boiler tubes
The material of the high-pressure boiler tube will creep because it works under high temperature and high pressure for a long time, resulting in a decline in plasticity and toughness, change of the original structure and corrosion. The steel pipe used for the boiler should have the following characteristics: steel pipes used for boilers should have sufficient durable strength and plastic deformation ability, minimum aging tendency and hot brittleness, good resistance to oxidation, coal ash, corrosion resistance at high temperatures in natural gas and steam, stress corrosion resistance, good organizational stability and process performance.

The steel types of high pressure boiler tubes include carbon steel, pearlite, ferrite and heat resistant austenitic stainless steel. In order to improve the thermal efficiency of thermal power generating units and reduce fuel consumption, countries all over the world have developed thermal power units with 1000MW, large capacity and high parameters at high temperature and pressure. The steam pressure has increased to 31.5 to 34.3MPa, and the superheated steam temperature has reached 595 to 650℃, which expand to the ultra-high pressure critical pressure.

This puts forward a higher requirement on the high pressure boiler tube. For this reason, new steel types have been developed to meet the need for high parameter power station boilers. Tubes used for heating surfaces of low and medium pressure boilers should have normally working pressure not more than 5.88Mpa and working temperatures below 450℃. Tubes used for heating surfaces of high-pressure boilers, economizers, superheaters, reheaters, petrochemical industry, etc. should have normally working pressure above 9.8Mpa and working temperature between 450℃ and 650℃.

Manufacturing methods of high pressure boiler tubes
① Generally, the temperature of boiler tubes is below 450℃. Domestic tubes are mainly made from No. 10 and No. 20 carbon steel hot-rolled tubes or cold-drawn tubes.
② High-pressure boiler tubes are often in high temperature and high pressure conditions when they are used. The tubes will oxidize and corrode under the action of high temperature flue gas and water vapor. The steel tube is required to have good enduring strength, oxidation, corrosion resistance and good organizational stability.

The advantages and disadvantages of hot rolled high pressure boiler tubes
Hot rolling is rolling above the recrystallization temperature, while cold rolling is rolling under the recrystallization temperature. Hot rolled high-pressure boiler tubes are divided into general steel tubes, low and medium pressure boiler steel tubes, high pressure boiler steel tubes, alloy steel tubes, stainless steel tubes, petroleum cracking tubes, geological steel tubes and other steel tubes.

The advantages of hot rolled high pressure boiler tubes
The grains of the steel can be refined and defects of the microstructure can be eliminated so that the steel structure can be dense and mechanical properties improved. This improvement is mainly reflected in the rolling direction, so that the steel is no longer isotropic to a certain extent.

Disadvantages of hot rolled high pressure boiler tubes
First, after hot rolling, the non-metallic inclusions in the steel are pressed into thin sheets, and delamination or interlayer occurs. Second, the residual stress is caused due to uneven cooling. Third, it’s difficult to control thickness and width of hot-rolled steel products.

Applications
① General boiler tubes are mainly used to make water wall tubes, boiling water tubes, superheated steam tubes, superheated steam tubes for locomotive boilers, large and small smoke tubes and arched brick tubes.
②High-pressure boiler tubes are mainly used to manufacture superheater tubes, reheater tubes, air guide tubes and main steam tubes of high-pressure and ultra-high-pressure boilers.

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