What are the key control points for sawing 20G high-pressure boiler steel pipes

Before and after sawing, the mechanical properties of 20G high-pressure boiler steel pipes must meet the requirements of GB 5310-2017 "Seamless Steel Pipes for High-Pressure Boilers" standard. Specific mechanical performance indicators and sawing-related analysis are as follows:

First, the core mechanical performance indicators of 20G high-pressure boiler steel pipes.
Tensile strength (Rm)
Range: 410-550 MPa
Significance: Reflects the material's resistance to fracture, ensuring the pipeline does not break under high pressure.
Yield strength (Rel)
Range: ≥245 MPa
Significance: The critical stress at which the material begins to undergo plastic deformation, ensuring the pipeline maintains its shape stability under pressure fluctuations.
Elongation after fracture (A)
Longitudinal: ≥24%
Transverse: ≥22%
Significance: Measures the material's plastic deformation capacity, ensuring the pipeline can withstand localized stress concentrations during installation or operation.
Impact Absorbed Energy (KV²/J) of 20G High-Pressure Boiler Steel Tubes:
Longitudinal: ≥40 J
Transverse: ≥27 J
Significance: Evaluates the material's resistance to brittle fracture under low temperature or impact loads, especially suitable for boiler systems in cold regions or with frequent start-ups and shutdowns.
Hardness of 20G High-Pressure Boiler Steel Tubes:
Brinell Hardness (HBW): 120-160
Vickers Hardness (HV): 120-160
Significance: Controls material hardness to avoid processing cracks while ensuring wear resistance.

Second, the Influence of Sawing on the Mechanical Properties of 20G High-Pressure Boiler Steel Tubes and Key Control Points:
Heat Affected Zone (HAZ) Softening or Hardening of 20G High-Pressure Boiler Steel Tubes:
Phenomenon: Sawing of 20G high-pressure boiler steel tubes (especially flame cutting) may generate localized high temperatures, leading to grain coarsening or phase transformation in the heat-affected zone, causing hardness fluctuations.
Control Measures: Cold sawing or diamond saw blades should be preferred for sawing 20G high-pressure boiler steel tubes to reduce heat input. If flame cutting is required, the cut surface must be normalized (air-cooled at 880-940℃) to restore material properties.
Residual Stress and Deformation of 20G High-Pressure Boiler Steel Pipes
Phenomenon: During the sawing process of 20G high-pressure boiler steel pipes, mechanical force may cause local plastic deformation of the pipe, generating residual stress.
Control Measures: After sawing, 20G high-pressure boiler steel pipes should undergo stress-relieving annealing (e.g., holding at 650℃ for 1-2 hours followed by slow cooling). Use symmetrical or segmented cutting processes to reduce single-time stress.
Surface Quality Requirements for 20G High-Pressure Boiler Steel Pipes
Standard: The sawn surface of 20G high-pressure boiler steel pipes should be smooth, free of burrs, cracks, or delamination, with a negative tolerance not exceeding 5%.
Inspection Methods for 20G High-Pressure Boiler Steel Pipes:
Visual Inspection: Confirm the absence of macroscopic defects.
Ultrasonic Testing (UT): Detect internal cracks (performed according to GB/T 5777).
Penetrating Test (PT): Inspect surface micro-cracks (applicable to non-magnetic materials).

Third, Performance Verification Recommendations for 20G High-Pressure Boiler Steel Tubes After Sawing:
Sampling Location: Take axial samples near the sawn end face of the 20G high-pressure boiler steel tube to test tensile strength, yield strength, and elongation after fracture.
Hardness Testing: Measure hardness in both the heat-affected zone and the base material area of the 20G high-pressure boiler steel tube, ensuring a hardness difference ≤ 15 HBW.
Impact Testing: For pipelines operating at low temperatures, a -20℃ impact test is required in the heat-affected zone, absorbing energy ≥ 27 J.

Fourth, Typical Application Scenarios and Performance Matching for 20G High-Pressure Boiler Steel Tubes:
High-Temperature and High-Pressure Steam Pipelines: Focus on verifying creep strength (e.g., creep rupture strength ≥ 100 MPa after 100,000 hours at 450℃).
Low-Temperature Economizer Tubes: Ensure impact energy absorption meets standards to avoid brittle fracture.
Irregular Shape Processing: For components such as elbows and tees, combine sawing and heat treatment processes to ensure overall performance uniformity.