Requirements, Inspection Details, and Applications of 25MnG High-Pressure Boiler Steel Pipes

First, the Standard Positioning and Scope of Application of 25MnG High-Pressure Boiler Steel Pipes

GB/T 5310-2023 is a national standard for seamless steel pipes for high-pressure boilers and above. It was issued on September 7, 2023, and officially implemented on April 1, 2024. 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 requirements of 25MnG material.

1. Chemical Composition: Element Content Range: Carbon (0.22-0.27%), a key element, ensures steel strength, but excessively high levels affect weldability and toughness. Silicon (0.17-0.37%) deoxidizes and improves steel strength. Manganese (0.70-1.00%) enhances strength and toughness and improves hot workability. Phosphorus (≤ 0.025%) is strictly controlled to prevent hot brittleness. Sulfur (≤ 0.015%) is strictly controlled to prevent cold brittleness. Chromium (≤ 0.25%), residual elements, improve corrosion resistance. Nickel (≤ 0.25%), residual elements, enhance toughness. Copper (≤ 0.20%), residual elements, and control impurity content. Molybdenum (≤ 0.15%) and residual elements improve high-temperature strength. Vanadium (≤ 0.08%), residual elements, refines grain size.

2. Mechanical Properties: Standard Values and Test Conditions: Tensile Strength (MPa): 485-640; Yield Strength (MPa): ≥275 for longitudinal specimens; Elongation (%): ≥20 for longitudinal specimens; Gauge length: 5 times the diameter; Impact Toughness (J/cm²): Meets standard requirements. Low-temperature testing.

3. Processing Performance

Heat Treatment: Normalizing (880-940°C) and tempering are typically used to optimize the 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 be within the permitted ranges specified in the standard.

Dimensional Tolerance: 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 and piping systems.

Third, Key Inspection and Testing Requirements for 25MnG High-Pressure Boiler Steel Pipes

Chemical Composition Analysis: Spectroscopic analysis and other methods are used to verify that the chemical composition meets standard requirements.

Mechanical Property Testing:

Tensile Testing: Yield Strength, Tensile Strength, and Elongation are tested.

Impact Testing: Low-Temperature Impact Toughness is tested.

Nondestructive Testing: Ultrasonic Testing: Detects internal defects in the steel pipe.

Eddy Current Testing: Detects surface defects in the steel pipe.

Hydraulic Testing: Verifies the pressure-bearing capacity of the steel pipe to ensure leak-free operation. Metallographic Observation: Ensures the structural stability of the steel pipe at high temperatures.

Fourth, Applications and Advantages of 25MnG High-Pressure Boiler Steel Pipes

Power Plant Boiler Industry:

Used in the manufacture of key components such as superheater tubes, reheater tubes, steam guide tubes, and main steam pipes for 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.

Petrochemical Industry:

Suitable for high-temperature and high-pressure piping systems such as cracking furnace tubes and heat exchangers.

Resists corrosion from corrosive media, ensuring long-term stable operation of equipment.

Nuclear Power Industry:

Used in heating surface tubes, headers, and piping for steam generators in nuclear power plants.

Meets the stringent material performance and reliability requirements of nuclear power equipment.

Fifth, Standard Updates and Optimizations

GB/T 5310-2023 has undergone numerous adjustments and optimizations compared to previous versions of the standard (such as GB/T 5310-2017):

Order Content: Relevant terms regarding order content 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 changed, 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 a heat-treated state, while stainless steel pipes must undergo heat treatment, pickling, and passivation.