Why are the Pipes for Industrial Boilers All Seamless Steel Pipes?
Industrial boiler tubes are mainly seamless steel pipes, because the various performance indicators of seamless steel pipes can fully meet the requirements of boiler applications. Although the cost is high, its safety and reliability are high. Welded steel pipes are generally used as low-pressure fluid delivery pipes within 2Mpa. Industrial boilers and other high-temperature and high-pressure equipment must use seamless steel pipes, and the wall thickness is also thickened accordingly.
Boiler seamless steel pipes are high-quality carbon steel, alloy steel and stainless heat-resistant seamless steel pipes used to manufacture the heating surface of high-pressure and above pressure water tube boilers. These boiler tubes often work under high temperature and high pressure. Under the action of high-temperature flue gas and water vapor, the tubes will oxidize and corrode. Therefore, the steel pipe is required to have high durability, high oxidation resistance and good organizational stability.
Now due to the rapid improvement of welding technology,
welded steel pipes are also widely used in medium and low-pressure boilers. For example, the friction welded steel pipe joints have consistent organizational structure. After the pipe joints are remelted by butt joints and corner joints, it is difficult to observe the butt marks with the naked eye, but the organization and quality of each part are exactly the same.
What is a seamless boiler tube?
Seamless boiler tube is a kind of boiler tube, belonging to the category of seamless tube, made of carbon steel or alloy steel. The manufacturing method is the same as that of seamless tube, but there are strict requirements on the type of steel used to manufacture steel tube.
Seamless boiler tube is often under high temperature and high pressure conditions during use. Under the action of high temperature flue gas and water vapor, the tube will undergo oxidation corrosion. The steel tube is required to have high durability, high anti-oxidation corrosion performance and good organizational stability. Seamless tubes for boilers are mainly used to manufacture superheater tubes, reheater tubes, air ducts, main steam pipes, etc. for medium pressure, high pressure and ultra-high pressure boilers. They are widely used in steam boilers, power generation, fossil fuel plants, industrial processing plants, power plants, etc.
What are the "four major pipelines" of power station boilers?
1. High-pressure feed water pipe: a pipeline for delivering feed water to the boiler. Including the pipeline from the check valve at the outlet of the feed water pump to the inlet header of the economizer.
2. Main steam pipeline: a pipeline used to transport superheated steam, which is an important device for the output of heat energy by the boiler. Includes the pipeline from the outlet header of the last superheater to the high-pressure main steam valve of the steam turbine (for boilers running in the main pipeline, to the valve before the main pipeline).
3. Reheat steam cold section pipeline: The pipeline that transports steam after one work to the reheater of the steam boiler. Includes the pipeline from the exhaust check valve of the steam turbine to the inlet header of the reheater.
4. Reheat steam hot section pipeline: The pipeline used to transport superheated steam heated by the reheater. Including the pipeline from the outlet header of the last stage reheater to the medium-pressure main steam valve of the turbine
Common standards and materials for seamless steel pipes for high-pressure boilers
The common standards for seamless steel pipes for high-pressure boilers currently used in China include GB 5310 domestic standards, ASME SA106, ASME SA209, ASME SA210, ASME SA213, ASME SA335 American standards, JIS B8230, JIS B8241 Japanese standards, DIN 17200, DIN 2448 German standards, ГОСТ4543, ГОСТ8731 Russian standards, etc.
At present, steel high-pressure boilers have been widely used in petrochemical, machinery, metallurgy, energy, light industry, national defense, environmental protection, ocean, space, life and other industrial sectors and scientific research fields in the world, with specifications of Φ10~1064mm and above. Many enterprises have the production capacity of high-pressure boiler tubes, and the steel types used are also very wide, including high-quality carbon steel 20G, manganese steel SA-106C, SA-210C, molybdenum steel 15Mo3, SA-209T1a, chrome-molybdenum steel SA-213T2, 15CrMoG, SA-213T22, chrome-molybdenum-vanadium steel 12Cr1MoVG, 12Cr2MoWVTiB (steel 102), SA-213T91, chrome-nickel steel SA-213TP304H, SA-213TP347H and other materials.
Comparison table of commonly used seamless steel pipe materials for high pressure boilers
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Seamless steel pipe grades for boilers
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characteristic
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Applicable working conditions
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Production standards
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20G
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① Good process performance, no temper brittleness
② Good anti-oxidation performance below 530℃
③ When operating at 470~480℃ for a long time, pearlite spheroidization and graphitization will occur.
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① Steam pipes and headers with wall temperature less than or equal to 425℃
② Heating surface tubes with wall temperature less than or equal to 450℃
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GB5310
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15CrMoG
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① Good cold working performance and welding performance
② Carbide spheroidization will occur when operating at 500~550℃ for a long time
③ It has high endurance strength and good anti-oxidation performance below 520℃
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① Steam pipes and headers with wall temperature less than or equal to 510℃
② Heating surface tubes with wall temperature less than or equal to 540℃
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GB5310
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12Cr1MoVG
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① Adding a small amount of vanadium to steel reduces the rate of alloy element transfer from ferrite to carbide. Dispersed vanadium carbides can strengthen the ferrite matrix.
② It still has high thermal strength and anti-oxidation properties at 580℃, and has high lasting shaping
③ The process performance and welding performance are good, but it is more sensitive and often has uneven impact toughness.
④ When tempered at 500~700℃, there is temper brittleness
⑤ Long-term operation at high temperature will cause pearlite spheroidization and alloy elements to transfer to carbides, resulting in a decrease in thermal strength.
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① Steam pipes and headers with wall temperature less than or equal to 555℃
② Heating surface tubes with wall temperature less than or equal to 540℃
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GB531
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Common problems in surface treatment and product processing of seamless steel pipes for high-pressure boilers:
1. The surface of seamless steel pipes for high-pressure boilers is inconsistent: only the welds are pickled and passivated, resulting in uneven surface and affecting the appearance.
2. Scratches on seamless steel pipes for high-pressure boilers are difficult to remove: the overall pickling and passivation, various scratches generated during the processing cannot be removed, and scratches and welding spatter attached to the stainless steel surface cannot be removed. Carbon steel, spatter and other impurities will cause chemical corrosion or electrochemical corrosion and rust in the presence of corrosive media.
3. Weld defects: Weld defects are relatively serious and can be compensated by manual and mechanical grinding. The resulting wear marks will make the surface uneven and affect the appearance.
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