Comparative Laboratory Investigation of Corrosion Processes in Welded and Non-welded Hull Steel Using Acoustic Emission Monitoring and Metallographic Analysis

Corrosion degradation of cargo and ballast tanks in marine structures strongly affects the operational lifetime and safety of floating units. Welded regions, including the weld metal and adjacent heat-affected zone, are particularly susceptible to localised corrosion due to microstructural heterogeneity and electrochemical differences. This paper describes a comparative laboratory investigation of the corrosion processes in welded and non-welded hull steel using acoustic emission monitoring supported by metallographic analysis. Accelerated corrosion tests were conducted using a KE-2 corrosion tester and a controlled corrosive solution to simulate an aggressive tank environment. Acoustic signals were continuously recorded using a Vallen AMSY-5 system equipped with VS-75 and VS-150 RIC sensors, and metallographic examination using optical microscopy was performed to characterise the corrosion pit morphology. The acoustic results confirmed the detectability of corrosion-related activity in both configurations, with clear separation of corrosion signals from background noise. However, despite the similar overall character of the acoustic responses in both cases, metallographic analysis revealed significantly different corrosion morphologies: numerous shallow pits were distributed across the surface of the non-welded specimen, whereas the welded specimen showed localised intensification with deeper pitting near the weld interface. This indicates that although acoustic emission is effective for real-time detection of active corrosion processes, it has a limited capability to distinguish the spatial characteristics and morphology of corrosion damage without complementary analysis. This study highlights both the potential and the limitations of acoustic emission monitoring in the assessment of corrosion processes in welded marine structures.