1. Chemical Composition Analysis
Testing Methods:
Direct-reading spectrometer: Rapidly measures the content of elements such as C, Si, Mn, P, and S.
Infrared C-S analyzer: Accurately analyzes carbon and sulfur elements, suitable for steelmaking raw materials and finished products.
N-O analyzer: Detects nitrogen and oxygen gas content, which affects the purity of the steel.
Key Indicators:
Harmful elements (As, Sn, Sb, Bi, Pb) must meet standard limits, such as GB9948 requirements of S≤0.015% and P≤0.025%.
2. Mechanical Performance Testing
Tensile test: Measures tensile strength (≥410MPa), yield strength (≥245MPa), and elongation (≥24%).
Impact test: Steel pipes with an outer diameter ≥76mm and wall thickness ≥14mm require low-temperature impact testing (e.g., at -40℃).
Hardness test: Brinell hardness (HB), Rockwell hardness (HRC), etc., must meet material standards.
3. Process Performance Verification
Flattening test: Evaluates the plastic deformation ability of the steel pipe; no cracks indicate qualification.
Flaring test: Simulates the flaring adaptability during pipe connection, with a mandrel cone angle of 30°~60°.
Bending test: Replaces the flattening test to verify the bending performance of large-diameter pipes.
4. Non-destructive Testing
Ultrasonic testing (UT): Detects internal cracks, delamination, and other defects, and must meet the C5 level standard of GB/T5777-1996.
Eddy current testing (ET): Sensitive to point defects, meeting the B-level requirements of GB/T7735-2004.
Magnetic particle testing (MT): Suitable for surface defect detection of ferromagnetic materials, the standard is C4 level of GB/T12606-1999. 5. Appearance and Dimensional Inspection
Surface quality: Visually inspect for defects such as cracks, folds, and scars. Low-quality pipes often appear light red or have excessive ovality.
Dimensional accuracy: Wall thickness deviation must be ≤ ±1.5% (precision pipes) or ±10% (ordinary pipes), and the outer diameter ovality error must be within the allowable range.
