Q1: What are the chemical composition inspection methods for Q345B steel pipe?
Spectroscopic analysis (OES) can quickly determine the main elements such as C, Si, and Mn with an accuracy of 0.001%. The carbon and sulfur analyzer is specifically used to detect the C and S content, using the infrared absorption principle. Inductively coupled plasma (ICP) is used for trace element analysis (such as P and As). When sampling, avoid the weld area and cut in the middle of the steel pipe. The test results must be compared with the GB/T 1591 standard to ensure that each element is within the allowable range.
Q2: How to test the mechanical properties of Q345B steel pipe?
The tensile test is based on the GB/T 228 standard, and the longitudinal specimen is taken to determine the yield strength, tensile strength and elongation. The impact test (GB/T 229) uses a Charpy V-notch specimen to test whether the -20℃ impact energy is ≥34J. Hardness test can be done with Brinell (HBW) or Rockwell (HRB) hardness tester, the standard value is ≤187HBW. Bending test checks whether there are cracks after 180° cold bending, and the diameter of the bending core is selected according to the standard. All tests must be completed in a third-party laboratory or a qualified in-plant laboratory.
Q3: What are the non-destructive testing technologies for Q345B steel pipes?
Ultrasonic testing (UT) can detect internal inclusions, delamination and other defects, with a sensitivity of Φ2mm equivalent. Radiographic testing (RT) is suitable for weld volume defect inspection, but the cost is relatively high. Magnetic particle testing (MT) is used for surface and near-surface crack detection, and it must be polished to Ra≤12.5μm first. Eddy current testing (ET) is suitable for rapid screening of large quantities of small-diameter pipes. Penetrant testing (PT) is used to inspect surface opening defects of non-magnetic materials.
Q4: How to control the dimensional tolerance of Q345B steel pipes?
The outer diameter tolerance is in accordance with GB/T 8162 standard, with the common grade being ±1.0% and the high grade being ±0.75%. The wall thickness deviation is usually ±10%, and the precision cold-drawn tube can be controlled within ±5%. The ovality requirement is not more than 80% of the outer diameter tolerance, and the curvature is ≤1.5mm/m. Length tolerance: fixed-length tube (+10~50mm), and multiple-length tubes need to reserve a cut margin. Calibrated calipers, micrometers and ring gauges are required for inspection.
Q5: What quality documents are required before Q345B steel pipes leave the factory?
A material certificate (including chemical composition and measured values of mechanical properties) must be provided. Third-party inspection reports (such as SGS, BV) are used for export or key projects. The non-destructive testing report must indicate the test method and qualified standards. The dimensional inspection record should contain measurement data of at least 3 sections. For special purposes (such as pressure vessels), heat treatment curves and process evaluation reports are also required.
