1. Appearance and Dimensional Inspection
Appearance Inspection: Observe whether the surface is smooth and free of defects such as cracks, folds, scars, scratches, bubbles, or oxide scale. High-quality steel pipes should have a uniform and smooth surface without obvious flaws.
Dimensional Accuracy: Use vernier calipers, micrometers, or ultrasonic thickness gauges to measure the outer diameter, wall thickness, length, and ovality to ensure compliance with standards such as GB/T 17395-2008. Wall thickness deviation is typically controlled within ±10%.
2. Non-Destructive Testing (NDT)
Used to detect internal and surface defects, it is a key means of ensuring safety:
Ultrasonic Testing (UT): Detects internal cracks, inclusions, delamination, and other defects. The standard is GB/T 5777-2019. It is sensitive to longitudinal and transverse defects.
Eddy Current Testing (ET): Suitable for surface point defects (such as pinholes and microcracks). It has a fast response speed and is suitable for online inspection.
Magnetic particle inspection (MT): For ferromagnetic materials, it can identify near-surface defects and is easy to operate.
Radiological inspection (RT): Used for imaging internal defects in thick-walled pipes, but it is more expensive and mostly used for critical components.
Electromagnetic ultrasonic testing: No coupling agent is required, and it can perform real-time testing on high-temperature, high-speed production lines, conforming to the new YB/T 6297-2024 standard.
✅ The latest standard GB/T 44152-2024 stipulates that from January 1, 2025, seamless steel pipes with an outer diameter ≥ 6mm must undergo ultrasonic testing within 300mm of the pipe end. Delamination defects with an area > 100mm² are considered unqualified.
3. Chemical composition analysis: C, Mn, Si, P, S, and alloying elements (such as Cr, Mo, Ni) are analyzed using direct-reading spectrometers, infrared carbon-sulfur analyzers, and other equipment to ensure that the material conforms to standards such as GB/T 3077 and ASTM A106. The composition of the finished product must be within the standard range; excessive deviation will affect strength and corrosion resistance.
4. Mechanical Property Testing
Tensile Test: Determines yield strength (YS), tensile strength (TS), and elongation (A) to verify the material's load-bearing capacity.
Impact Test: Assesses low-temperature toughness, commonly using the CVN method, to ensure the steel pipe does not fracture brittlely in cold environments.
Hardness Test: Uses a Brinell (HB) or Rockwell (HRC) hardness tester to determine material uniformity and processing performance.
Hydraulic Pressure Test: Conducts a pressure test at 1.5 times the working pressure for at least 10 seconds; no leakage is acceptable. This is a mandatory inspection item before shipment.
5. Process Performance and Metallographic Analysis
Flattening Test: Simulates the deformation capacity during pipe connection to check for cracking.
Flanging and Bending Test: Verifies processing adaptability.
Metallographic Inspection: Observes the microstructure, such as grain size, non-metallic inclusions, and decarburized layer, using a microscope to ensure uniform microstructure.
