Failure Analysis of Ladle Leakage and Wall Deposit Formation with Low-Nickel Slag Converter in Rotary Kiln–Electric Furnace Nickel Smelting (RKEF)

Abstract

Rotary Kiln Electric Furnace (RKEF) uses ladles to transfer high- and low-nickel slag from the converter at approximately 1200 °C. In 2023, a ladle leak occurred during high-nickel slag handling, cause serious safety and operational risks. This incident necessitated a failure analysis to evaluate ladle material suitability, degradation mechanisms, and the role of slag deposits in ladle integrity. Failure analysis was conducted with Optical Emission Spectroscopy, microstructure test, X-ray Fluorescence, X-ray Diffraction, Scanning Electron Microscopy–Energy Dispersive X-ray, thickness measurement using Non-Destructive Testing, thermal camera, and deposit volume evaluation. Both old (pre-2020) and new (post-2020) ladles were examined. From the test, both ladle types met with ASTM A27 Grade 30–60 specifications. But old ladle categorizes as medium carbon steel (pearlite phase identified) while new ladle categorizes as low carbon steel (ferrite phase identified). Ladle failure was primarily caused by localized mechanical load at the hook ladle during initial high-nickel slag pouring, combined with the absence of a protective low-nickel slag deposit layer, allowing high-nickel slag penetration at elevated temperatures (initial ladle thickness 90 mm, after incident became 39 mm). SEM-EDX identified slag-related compounds, nickel oxide (NiO), which reacted with iron (Fe) to form iron (II) oxide (FeO), inducing pitting corrosion and failure initiation. Adequate deposit volume during low-nickel slag service provided thermal and chemical protection. Ladles operated at a safe temperature (~335 °C) with a reduced risk of leakage during high-nickel slag and matte handling after the fifth low-nickel slag cycle.