Analysis of Corrosion Behaviour of Welded Austenitic Stainless Steel Immersed in Aqueous Alkaline Medium

Aims: This research is aimed at investigating the corrosion behaviour of welded austenitic stainless steel (ASS) immersed in an alkaline sodium hydroxide medium. The tensile properties of the structure were also determined.

Study Design: Weight loss method, Factorial Design of Experiment and scanning electron microscope were used for the analysis.

Place and Duration of Study: Department of Mechanical Engineering, Ahmadu Bello University, Zaria, Nigeria, between March and November, 2014.

Methodology: The corrosion behaviour of type 304 austenitic stainless steel (ASS) immersed in sodium hydroxide (NaOH) medium (0.5 M) at ambient temperatures was investigated using conventional weight loss method together with factorial design of experiment, scanning electron microscopy (SEM), Gas metal arc welding machine. The design expert was used to determine the surface responses and interactions between the parameters; SEM was used to examine the test specimen microstructural analysis after immersion in the basic medium while the Monsanto Tensometer was used to examine material optimum performance in hydrochloric acid medium in terms of strength.

Results: It was found that tensile strength increased with increasing welding parameters (from 189 MN/m2 to 203 MN/m2). It was also found that increase in welding current and speed at constant voltage gave the optimum performance of the ASS structure in NaOH medium obtained at speed 40 mm/sec and current 110 Amp. Surface corrosion deposit composition was analyzed with the SEM paired with energy dispersive spectrometer (EDS).

Conclusion: This research shows that corrosion susceptibility of ASS in sodium hydroxide medium during the exposure time period studied is due to the aggressiveness of the hydroxyl ion (–OH). The materials’ susceptibility to stress corrosion cracking was conspicuous after a successful corrosion analysis in the medium with a tensile test results. It was concluded that relatively high speed and current at a constant voltage gave a satisfactory weldment of the structure.