Q1: What are the main international standards for Q390 steel pipes?
ASTM A572 Grade 50 (American standard) has similar performance to Q390 but has a higher upper limit of Mn content (1.35%). S460QL of EN 10025-6 (European standard) achieves similar strength through quenching and tempering. SM570 of JIS G3114 (Japanese standard) requires the addition of 0.02% Ti to ensure toughness. ISO 630-5 classifies this type of steel as E460 grade. GB/T 1591-2018 is the core standard of China, which subdivides five quality grades of Q390A-E, among which Q390D requires an impact energy of ≥34J at -20℃.
Q2: What is the chemical composition test method for Q390 steel pipes?
Spark direct reading spectrometer (OES) is used for rapid analysis before the furnace with an accuracy of 0.001%. Inductively coupled plasma (ICP-MS) can detect trace elements such as Nb and V. The carbon and sulfur analyzer uses infrared absorption method with an error of ±0.002%. Sampling needs to be drilled at 1/4 thickness of the steel plate to avoid segregation. Third-party testing must be carried out according to GB/T 4336-2016, with at least 3 specimens per furnace number.
Q3: How to test the mechanical properties of Q390 steel pipe?
The tensile test is processed according to GB/T 228.1 for round bar specimens (Lo=5d), and the rate is controlled at 2mm/min to 5% after yield. The impact test uses a 10×10×55mm V-notch specimen, and the cryogenic box needs to be precooled to -40±2℃. The bending test (d=3a) requires 180° without cracking to evaluate the plastic deformation capacity. The hardness test Brinell (HBW), Rockwell (HRC) or Vickers (HV) method needs to be selected according to the wall thickness. The laboratory needs to be certified by CNAS and the equipment is calibrated regularly.
Q4: What are the technical points of non-destructive testing of Q390 steel pipes?
Ultrasonic flaw detection (UT) uses a 5MHz dual crystal probe with a sensitivity of Φ1.6mm flat bottom hole. Radiographic testing (RT) uses Ir192 or X-ray machine, and the image quality meter index is ≥12. TOFD technology can detect cracks with a depth of 0.5mm and a positioning accuracy of ±1mm. Eddy current testing (ET) is suitable for surface opening defects, and the frequency selection is 60-120kHz. Phased array ultrasound (PAUT) can achieve three-dimensional imaging of welds, and the data can be traced and stored for 20 years.
Q5: What quality documents are required for Q390 steel pipes to be provided before leaving the factory?
The quality certificate must include the furnace number, batch number, specifications and all test data (in accordance with GB/T 2102-2006). Third-party SGS/BV test reports are essential for export products. The material traceability system must record the parameters of the entire process of steelmaking-rolling-heat treatment. Special uses also require NDT reports and HIC/SSC corrosion resistance test certificates. EU projects must meet CE certification and EN 10204 3.1 type certificate requirements.
