High pressure boiler tube is a kind of boiler tube, which belongs to seamless steel tube category. The manufacturing method is the same as that of seamless tube high pressure boiler tubes, but there are strict requirements for the steel grades used in manufacturing steel tubes. High pressure boiler tubes are often used in high temperature and high pressure conditions. High-pressure boiler tubes are mainly used to manufacture superheater tubes, reheater tubes, air ducts and main steam pipes of high-pressure and ultra-high-pressure boilers.
Due to the long-term work under high temperature and high pressure, the material will creep, the plasticity and toughness will decrease, the original structure will change, and the corrosion will occur. As steel tubes for boilers, they should have:
(1) sufficient endurance strength;
(2) adequate plastic deformation capacity;
(3) minimum aging tendency and thermal brittleness;
(4) high corrosion resistance, coal ash resistance, natural gas high temperature corrosion, steam and stress corrosion resistance.
(5) good organizational stability and good process performance. High pressure boiler tubes have carbon steel and pearlite, ferrite and austenitic stainless steel. In order to improve the thermal efficiency and reduce burnup of thermal power generating units, most countries in the world are developing large capacity, high parameter (high temperature and high pressure) thermal power generating units (1000MW or above). The steam
pressure increases to 31.5 ~ 34.3MPa, the superheated steam temperature reaches 595~650 degrees, and develops towards the critical pressure of ultra high pressure, which puts forward higher requirements for high-pressure boiler tubes. A new type of steel has been developed to meet the needs of high parameter utility boilers.
Manufacture and application of high pressure boiler pipe
(1) Manufacturing methods:
① General boiler Tube use temperature below 450 ℃, domestic tubes are mainly made of 10th, No. 20th Carbon-knot steel hot-rolled pipe or cold-drawn pipe.
② High-pressure boiler tubes are often used in high temperature and high pressure conditions when the tube in high temperature flue gas and water vapor action, oxidation and corrosion will occur. The steel pipe is required to have high lasting strength, high antioxidant corrosion resistance, and good tissue stability.
①general boiler tubes are mainly used for manufacturing water wall tubes, boiling water pipes, superheated steam pipes, superheated steam pipes for locomotives and boilers, large and small smoke pipes and arched brick pipes.
②High pressure boiler tubes are mainly used to manufacture superheater tubes, reheater tubes, gas pipes and main steam pipes of high pressure and extra high pressure boilers.
The production process of high pressure boiler tubes varies with different steel grades. Taking pearlite chrome molybdenum vanadium steel as an example, the characteristics of boiler tube production are:
(1) tube blanks should be peeled and the amount of peeling is usually 5mm.
(2) because the steel is hard, the tube billet is mostly cut or sawed by oxygen.
(3) because the thermal conductivity of chrome molybdenum vanadium steel is lower than that of carbon steel, the heating speed should be slightly slower, the heating temperature is 1120~1180 degrees, and the perforation temperature is 1100~1160 degrees.
(4) this kind of steel has good plasticity and low deformation resistance at 1000~1100 degree interval, so the perforation performance is good, and the deformation parameters can be selected as medium carbon steel or alloy steel (for example, 30CrMnSiA).
(5) after normalizing and tempering, the normalizing temperature is 950~980 C, the tempering temperature is 730~750 C, and the holding time is 2 ~ 3H.
(6) steel pipe size tolerance is stricter, so as to ensure the corresponding welding. The length of the pipe is as long as possible, so as to reduce the number of welded joints.