Boiler tube is a type of seamless tube. The manufacturing method is the same as that of seamless pipes, but there are strict requirements on the steel grades used to manufacture steel pipes. According to the temperature of use, it is divided into two types: general boiler tubes and high-pressure boiler tubes.
The mechanical properties of boiler tubes are important indicators to ensure the final performance (mechanical properties) of steel, which depends on the chemical composition and heat treatment system of the steel. In the steel pipe standard, according to different use requirements, the tensile properties (tensile strength, yield strength or yield point, elongation), hardness and toughness indicators, as well as high and low temperature properties required by users are specified.
1) Generally, boiler tubes are made of hot-rolled or cold-drawn tubes with a temperature below 350 °C.
2) High-pressure boiler tubes are often used in high temperature and high pressure conditions, and the tubes will be oxidized and corroded under the action of high-temperature flue gas and water vapor. The steel pipe is required to have high lasting strength, high oxidation corrosion resistance, and good organizational stability.
Folding specifications and appearance
1) Specifications of steel pipes for structural boilers, with an outer diameter of 10~426mm, a total of 43 types. There are 29 types of wall thicknesses ranging from 1.5 to 26 mm. However, the outer diameter and wall thickness of superheated steam pipes, large smoke pipes, small smoke pipes and arch brick pipes for locomotive boilers are otherwise specified.
2) The outer diameter of the hot-rolled tube is 22~530mm, and the wall thickness is 20~70mm. The outer diameter of the cold drawn (cold rolled) pipe is 10~108mm, and the wall thickness is 2.0~13.0mm.
3) Appearance quality: There are no cracks, folds, folds, scars, delaminations and hairlines on the inner and outer surfaces of the steel pipe. These defects should be completely removed. The cleaning depth shall not exceed the negative deviation of the nominal wall thickness, and the actual wall thickness at the cleaning place shall not be less than the minimum allowable wall thickness.
Quality Control of Boiler Tubes
1) Tube blank control
The tube blank has a great influence on the production of seamless boiler tubes, mainly in terms of the stability of the chemical composition of the steel and the purity of the steel. In recent years, with the substantial improvement of the level of metallurgical technology and equipment, the production process of continuous casting and rolling of tube billets has been rapidly promoted due to its advantages of high efficiency, low consumption, high quality and low cost. In order to ensure the surface quality, the tube blank factory is generally equipped with testing methods such as magnetic flux leakage detection of steel rods, ultrasonic phased array flaw detection or infrared flaw detection, and related supporting means such as surface peeling when defects are found.
2) Control points of heat treatment process
In the production process of seamless steel pipes for boilers, heat treatment is the key process.
Heat treatment has an important impact on the inherent quality and surface quality of seamless steel pipes, especially for the production of alloy seamless steel pipes, and has a great impact on the lasting performance of high-pressure boiler tubes for power station boilers.
Stable metallographic structure and good inner and outer surface quality represent the manufacturing level of steel pipe enterprises.
3) Control of non-destructive testing
Generally, the non-destructive testing of high-pressure boiler tubes generally adopts eddy current and ultrasonic automatic flaw detection, which requires eddy current flaw detection of steel pipes one by one.
The mechanical properties of boiler tubes are important indicators to ensure the final performance (mechanical properties) of steel, which depends on the chemical composition and heat treatment system of the steel. In the steel pipe standard, according to different use requirements, the tensile properties (tensile strength, yield strength or yield point, elongation), hardness and toughness indicators, as well as high and low temperature properties required by users are specified.
1) Generally, boiler tubes are made of hot-rolled or cold-drawn tubes with a temperature below 350 °C.
2) High-pressure boiler tubes are often used in high temperature and high pressure conditions, and the tubes will be oxidized and corroded under the action of high-temperature flue gas and water vapor. The steel pipe is required to have high lasting strength, high oxidation corrosion resistance, and good organizational stability.
Folding specifications and appearance
1) Specifications of steel pipes for structural boilers, with an outer diameter of 10~426mm, a total of 43 types. There are 29 types of wall thicknesses ranging from 1.5 to 26 mm. However, the outer diameter and wall thickness of superheated steam pipes, large smoke pipes, small smoke pipes and arch brick pipes for locomotive boilers are otherwise specified.
2) The outer diameter of the hot-rolled tube is 22~530mm, and the wall thickness is 20~70mm. The outer diameter of the cold drawn (cold rolled) pipe is 10~108mm, and the wall thickness is 2.0~13.0mm.
3) Appearance quality: There are no cracks, folds, folds, scars, delaminations and hairlines on the inner and outer surfaces of the steel pipe. These defects should be completely removed. The cleaning depth shall not exceed the negative deviation of the nominal wall thickness, and the actual wall thickness at the cleaning place shall not be less than the minimum allowable wall thickness.
Quality Control of Boiler Tubes
1) Tube blank control
The tube blank has a great influence on the production of seamless boiler tubes, mainly in terms of the stability of the chemical composition of the steel and the purity of the steel. In recent years, with the substantial improvement of the level of metallurgical technology and equipment, the production process of continuous casting and rolling of tube billets has been rapidly promoted due to its advantages of high efficiency, low consumption, high quality and low cost. In order to ensure the surface quality, the tube blank factory is generally equipped with testing methods such as magnetic flux leakage detection of steel rods, ultrasonic phased array flaw detection or infrared flaw detection, and related supporting means such as surface peeling when defects are found.
2) Control points of heat treatment process
In the production process of seamless steel pipes for boilers, heat treatment is the key process.
Heat treatment has an important impact on the inherent quality and surface quality of seamless steel pipes, especially for the production of alloy seamless steel pipes, and has a great impact on the lasting performance of high-pressure boiler tubes for power station boilers.
Stable metallographic structure and good inner and outer surface quality represent the manufacturing level of steel pipe enterprises.
3) Control of non-destructive testing
Generally, the non-destructive testing of high-pressure boiler tubes generally adopts eddy current and ultrasonic automatic flaw detection, which requires eddy current flaw detection of steel pipes one by one.
