ERW straight seam steel pipe passes process performance inspection

ERW straight seam steel pipe, manufactured under the API 5L standard, has become a core steel pipe for oil and gas transportation thanks to its rigorous process control and comprehensive performance testing system. The reliability of its process performance is primarily reflected in the following key aspects:

ERW steel pipe utilizes high-frequency induction heating technology, precisely controlling the welding temperature gradient and extrusion pressure to ensure a metallurgical bond between the weld metal and the base material. For example, during the welding process of API 5LGr.BPSL2 steel pipe, real-time monitoring of heat input parameters is required to maintain a stable fusion zone width within a range of 3-5mm to avoid grain coarsening or lack of fusion defects caused by overheating. Companies such as Hebei Meide Steel Pipe have increased their welding qualification rate to 99.7% by introducing intelligent temperature control systems, significantly reducing the risk of weld brittleness.

To address residual stress issues in ERW steel pipe welds, the industry generally adopts online medium-frequency induction normalizing. This process homogenizes the weld structure and eliminates hardening phases by precisely controlling the heating temperature (920-950°C) and holding time (5-15 minutes). For example, one company's combined normalizing and tempering process 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 pipe-end radiographic testing of ERW steel pipes. The test blocks are N10 notches (3.2mm depth) or 1.6mm vertical through-holes, with an acceptance threshold set at 100% wave height. This allows for accurate identification of internal defects larger than 0.5mm. For specialized applications such as submarine pipelines, the DNVOS-F101 standard further requires the addition of Time-of-Flight Diffraction (TOFD) testing to ensure the complete weld cross-section is free of blind spots.

Each batch of steel pipe undergoes expansion tests (expansion rate 8%), flattening tests (flattening to 2/3 of the outer diameter), and hydraulic tests (holding pressure at 1.5 times the design pressure for 10 seconds) to verify its plasticity reserve and pressure-bearing capacity. For example, X65M steel grade has a stable yield strength between 450 and 480 MPa, and an elongation at break of ≥25%, fully meeting the performance requirements of the API 5L standard for medium- and high-strength pipeline steel.