The selection of seamless pipes for industrial steam is crucial because it is directly related to the safety, efficiency and life of the system operation. Steam systems usually involve high temperatures and high pressures, so there are strict requirements on the material, strength, corrosion resistance and manufacturing standards of steel pipes. The following is a careful summary of the key considerations for seamless pipes for industrial steam:
Key performance requirements
1. High temperature resistance: Steam temperatures can range from over 100°C for saturated steam to several hundred degrees Celsius for superheated steam. Steel pipes need to be able to withstand long-term high temperatures without creep (slow plastic deformation over time under constant stress) or oxidation failure.
2. High-pressure resistance: The pressure of steam pipelines ranges from low pressure (a few bar) to ultra-high pressure (hundreds of bar). Steel pipes must have sufficient yield strength and tensile strength to withstand the design pressure and ensure that the pipeline will not burst or leak.
3. Corrosion resistance: Steam may contain oxygen, carbon dioxide or other impurities, which may cause internal corrosion of the pipeline. The external environment (such as moisture, chemical exposure) may also cause corrosion. The steel pipe should have corresponding corrosion resistance.
4. Good toughness: Even under high temperature and high pressure, the steel pipe should maintain a certain toughness to prevent brittle fracture.
5. Excellent weldability: Steam pipelines usually require on-site welding connections, so the steel pipe material must have good welding performance to ensure the quality of the weld.
6. Dimensional stability: At high temperatures, the thermal expansion of the steel pipe should be controlled within the allowable range and maintain dimensional stability.
Common materials and standards
Depending on the temperature and pressure level of the steam, seamless steel pipes of different materials will be selected and the corresponding standards will be followed:
Suitable for steam systems with medium to low pressure and medium temperature.
ASTM A106 (or ASME SA-106):
Features: This is the most commonly used seamless carbon steel pipe in industrial steam piping, suitable for high-temperature and high-pressure conditions. It comes in three grades: A, B, and C, with Grade B (A106 Gr. B) being the most commonly used. A106 pipe exhibits excellent mechanical properties in high-temperature environments, including high tensile strength and yield strength. Its chemical composition contains silicon, which can enhance its performance in high-temperature environments.
ASTM A53 (or ASME SA-53):
Features: Suitable for general mechanical and pressure applications, and can also be used for general-purpose steam, water, gas, and air piping. Compared to A106, A53 is typically used for lower-pressure steam systems. It is available in two grades, A and B, and in both seamless and electric resistance welded (ERW) construction styles (seamless is generally preferred for steam applications).
Applications: Low-pressure steam systems and structural pipe.
Carbon steel grades (e.g., 20# steel) in GB/T 8163 "Seamless Steel Tubes for Fluid Transport":
Features: Suitable for general fluid transport, including some low- and medium-pressure steam applications. However, for higher-pressure or high-temperature steam, more specialized boiler tube standards are typically used.
GB/T 3087 "Seamless Steel Tubes for Low- and Medium-Pressure Boilers":
Features: Specially used for manufacturing superheated steam pipes and boiling water pipes for low- and medium-pressure boilers. Typically made of high-quality carbon structural steel.
2. Alloy Steel Seamless Pipe
Suitable for high temperature and high pressure, especially ultra-high pressure and supercritical steam systems, or places with creep requirements, these steel pipes are added with alloying elements such as chromium (Cr), molybdenum (Mo), and vanadium (V) to improve their high temperature strength, creep resistance and oxidation resistance.
ASTM A335 (or ASME SA-335):
Features: This standard specifies seamless ferritic alloy steel pipes for high-temperature use, covering a variety of grades, such as P11, P22, P91, and P92. These grades exhibit excellent strength and creep resistance at high temperatures, making them the preferred choice for core components such as main steam pipes and reheater tubes in supercritical and ultra-supercritical power plants.
P11/P22: A medium chromium-molybdenum steel, widely used in subcritical and supercritical boiler systems.
P91/P92: It is a high-grade martensitic stainless steel with higher high-temperature strength and creep resistance, and is used in ultra-supercritical power plants.
GB/T 5310 Seamless Steel Tubes for High-Pressure Boilers:
Features: High-pressure boiler steel pipes comply with international standards, covering a variety of high-quality carbon steel, alloy steel, and stainless heat-resistant steel grades, suitable for the heating surface of water-tube boilers with high pressure and above, such as 12Cr1MoV, 15CrMoG, etc.
3. Stainless Steel Seamless Pipe
It is suitable for steam systems with extremely high requirements for corrosion resistance, or in special media environments (such as humidity and high chloride ion content) to prevent corrosion and pollution.
ASTM A312 (or ASME SA-312):
Features: Covers a variety of austenitic stainless steel (such as TP304, TP304L, TP316, TP316L, etc.) and duplex stainless steel seamless and welded pipes. 304/316 series stainless steel has excellent corrosion resistance and is used in clean steam, food-grade steam or in the presence of corrosive condensate.
Applications: pharmaceutical, food, fine chemicals, high-purity steam systems, etc.
Other important considerations
Wall thickness (Schedule): The wall thickness selection of steam pipes is crucial and needs to be calculated based on the design pressure, temperature, and material. Common schedules include Schedule 40 (Sch.40), Schedule 80 (Sch.80), Schedule 160 (Sch.160), etc. A higher schedule number indicates a thicker wall thickness.
Connection method: Welding connection is usually used to ensure sealing and overall strength under high pressure. Flange connection is also used to connect equipment or valves.
Heat treatment: Many alloy steel pipes used for high-temperature steam undergo specific heat treatment (such as normalizing, tempering, and quenching and tempering) after production to optimize their mechanical properties and organizational structure.
Non-destructive testing (NDT): Strict non-destructive testing (NDT) is key to ensuring the quality of steam pipelines, including ultrasonic testing (UT), radiographic testing (RT), magnetic particle testing (MT), or penetrant testing (PT).
Water pressure test: All steam steel pipes must undergo a water pressure test before leaving the factory to verify their pressure bearing capacity and sealing.
Read more: Seamless Pipe for Oil Transportation
