API 5L ERW Straight Seam Steel Pipe Passes Process Performance Inspection

ERW straight seam steel pipes, manufactured under the API 5L standard, have become core steel pipes in the oil and gas transportation field due to their rigorous process control and comprehensive performance inspection system. The reliability of their process performance is mainly reflected in the following key aspects:

ERW steel pipes utilize high-frequency induction heating technology. By precisely controlling the welding temperature gradient and extrusion pressure, metallurgical bonding between the weld metal and the base metal is ensured. Taking API 5L Gr.B PSL2 grade steel pipe as an example, heat input parameters must be monitored in real time during the welding process to keep the weld fusion zone width stable within the range of 3-5mm, avoiding grain coarsening or incomplete fusion defects caused by overheating.

To address the residual stress problem in ERW steel pipe welding, the industry generally adopts online medium-frequency induction normalizing treatment. This process, through precise control of heating temperature (920-950℃) and holding time (5-15 minutes), homogenizes the weld microstructure and eliminates hardened phases. For example, after adopting a combined normalizing and tempering process, a company increased the Charpy impact energy of its steel pipe welds at -20°C from 40J to 70J, meeting the transportation requirements of polar oil and gas fields.

The API 5L standard mandates 100% ultrasonic testing and end-to-end radiographic testing for ERW steel pipes. The test comparison blocks use N10 grooves (3.2mm depth) or 1.6mm vertical through holes, with the acceptance limit set at 100% wave height, accurately identifying internal defects larger than 0.5mm. For special conditions such as subsea pipelines, the DNVOS-F101 standard further requires the addition of Time-of-Flight (TOFD) diffraction testing to ensure no blind spots across the entire weld cross-section.

Each batch of steel pipes must undergo a flaring test (8% flaring rate), a flattening test (flattened to 2/3 of the outer diameter), and a hydraulic test (1.5 times the design pressure held for 10 seconds) to verify its plasticity reserve and pressure-bearing capacity. Taking X65M steel grade as an example, its measured yield strength is stable in the range of 450-480MPa, and its elongation at break is ≥25%, which fully meets the performance requirements of API 5L standard for medium and high strength pipeline steel.