How to Inspect Weld Quality in ERW Steel Pipes

Electric Resistance Welded (ERW) pipes are manufactured by cold-forming a ribbon of steel into a cylindrical shape and passing an electric current through the edges to create a longitudinal seam. Because the weld is the most vulnerable part of the pipe, rigorous inspection is mandatory.

The inspection process starts with Visual Testing (VT). Inspectors look for surface irregularities such as undercut, overlap, or porosity. However, many defects are internal and require Non-Destructive Testing (NDT).

Ultrasonic Testing (UT) is the most common method for ERW pipes. High-frequency sound waves are pulsed through the weld seam. If a crack or inclusion exists, the sound wave reflects back earlier than expected, revealing the flaw’s location and size. Another critical check is the Hydrostatic Test, where the pipe is filled with water and pressurized to a level significantly higher than its operating limit.

Finally, for high-end applications, a Flattening Test is performed on samples from the production line. A section of the pipe is compressed until the walls meet. If the weld cracks before a specific distance is reached, the batch is rejected. Professional inspection ensures that the pipe can handle the stresses of thermal expansion and internal pressure fluctuations without seam failure.