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

Dorota Tyrala,Bogdan Pawlowski

doi:10.1007/s11668-021-01134-6

Dorota Tyrala, Bogdan Pawlowski

Open Access

https://doi.org/10.1007/s11668-021-01134-6

Copy DOI

Abstract

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.

Highlights

Visual inspection of the failed pipe showed that the rupture is located within the seam weld line, to the case presented in the work [1], which focused on longitudinal cracks in electric resistance welded (ERW) steel pipes immediately after quenching and tempering processes
As stated by Kaba et al [1], the cracks in the quenched and tempered ERW steel pipes could be correlated with the combination of coarse manganese silicate type complex oxide formation in the weld seam and high
In the case of the pipe examined in this study, the longitudinal crack occurred after just 2 years of service and the pipe itself was not subjected to heat treatment after HF induction welding

Summary

Introduction

Visual inspection of the failed pipe showed that the rupture is located within the seam weld line, to the case presented in the work [1], which focused on longitudinal cracks in electric resistance welded (ERW) steel pipes immediately after quenching and tempering processes. The high-frequency current, introduced with an induction coil around the pipe, flows only on the surface of the pipe (skin effect) and the edges of the coil material are heated up to high temperatures forged with external rolls and some metal is expelled (squeezed out) together with the iron oxides formed during heating [6].

Results

Conclusion