First, the Standard Definition and Scope of Application of
25MnG High-Pressure Boiler Steel Pipes
GB/T5310-2023 is a national standard for seamless steel pipes for high-pressure boilers and above. This standard specifically applies to:
- Key components of high-pressure and ultra-high-pressure boilers, such as superheaters, reheaters, and main steam pipes;
- High-temperature and high-pressure piping systems in the petrochemical, power, and other fields;
- Seamless steel pipes for other high-temperature and pressure-bearing equipment.
Second, the core material requirements for 25MnG high-pressure boiler steel pipes.
1. Chemical Composition:
Carbon: 0.22-0.27% ensures steel strength, but too high a concentration affects weldability and toughness.
Silicon: 0.17-0.37% deoxidizes and increases steel strength.
Manganese: 0.70-1.00% enhances strength and toughness, improving hot working properties.
Phosphorus: ≤0.025, strictly controlled to prevent hot brittleness.
Sulfur: ≤0.015, strictly controlled to prevent cold brittleness.
Chromium: ≤0.25 residual element, improves corrosion resistance.
Nickel: ≤0.25 residual element, enhances toughness.
Copper: ≤0.20 residual element. Elements to control impurity content
Molybdenum: ≤0.15 residual elements, improves high-temperature strength
Vanadium: ≤0.08 residual elements, refines grain size
2. Mechanical Properties: Standard Values and Test Conditions
Tensile Strength (MPa): 485-640 (longitudinal specimens)
Yield Strength (MPa): ≥275 (longitudinal specimens after fracture)
Elongation (%): ≥20 (gauge length, 5 times)
Diameter Impact Toughness (J/cm²): Meets standard requirements, tested in a low-temperature environment
3. Processing Performance
-Heat Treatment: Normalizing (880-940°C) followed by tempering is typically used to optimize microstructure and enhance creep resistance.
-Surface Quality: The surface should be smooth, free of defects such as cracks, folds, and scars. The depth and length of minor scratches and pits must fall within the standard tolerances.
-Dimensional Tolerances: The outer diameter and wall thickness tolerances must be strictly controlled within the standard range to ensure compliance with the installation and use requirements of high-pressure equipment piping systems.
Third, Key Inspection and Testing Requirements for 25MnG High-Pressure Boiler Steel Pipes
1. Chemical Composition Analysis: Verify that the chemical composition meets standard requirements through methods such as spectral analysis.
2. Mechanical Property Testing:
-Tensile Testing: Test yield strength, tensile strength, and elongation.
-Impact Testing: Examine impact toughness in low-temperature environments.
3. Nondestructive Testing:
-Ultrasonic Testing: Detect internal defects in the steel pipe.
-Eddy Current Testing: Detect surface defects in the steel pipe.
-Hydraulic Testing: Verify the pressure-bearing capacity of the steel pipe and ensure leak-free operation.
-Metallographic Observation: Ensure the structural stability of the steel pipe at high temperatures.
Fourth, Applications and Advantages of 25MnG High-Pressure Boiler Steel Pipes
1. Power Plant Boiler Industry: Used in the manufacture of key components such as superheater tubes, reheater tubes, steam guide tubes, and main steam pipes in high-pressure and ultra-high-pressure boilers. The long-term operating temperature should not exceed 550°C to avoid performance degradation due to pearlite spheroidization. 2. Petrochemical Industry: Suitable for high-temperature and high-pressure piping systems, such as cracking furnace tubes and heat exchangers. It resists corrosion from corrosive media and ensures long-term, stable operation of the equipment.
3. Nuclear Power Industry: Used in heating surface tubes, headers, and piping for steam generators in nuclear power plants. It meets the stringent material performance and reliability requirements of nuclear power equipment.
Fifth, Standard Updates and Optimizations for 25MnG High-Pressure Boiler Steel Pipes
GB/T5310-2023 has undergone numerous adjustments and optimizations compared to previous versions of the standard (such as GB/T5310-2017):
-Ordering Details: Relevant clauses in the ordering details have been revised to adapt to market demand and production practices.
-Dimensional Tolerances: The allowable deviations for outer diameter and wall thickness have been refined, improving dimensional accuracy.
-Chemical Composition: The chemical composition requirements for specific grades (such as 25MnG) have been revised, and requirements for the control of harmful elements have been added.
-Delivery Condition: It has been clarified that carbon steel and alloy steel must be delivered in the heat-treated state, while stainless steel pipes must undergo heat treatment, pickling, and passivation.
