Failure Analysis of Premature Corrosion of HF Seam-Welded Steel Pipe in Central Heating System

Premature corrosion in the form of longitudinal cracking in a high-frequency (HF) induction seam-welded steel pipe occurred after just 24 months in service. The failed pipe was investigated to reveal the main cause of its failure, and the results of microstructural examinations (light optical microscopy, scanning electron microscopy with energy-dispersive spectrometry) suggest that the failure resulted from an HF induction welding process defect—a so-called cast weld , that is, a huge number of iron oxides in the weld line caused by insufficient ejection of the molten metal from the bond line.