Accelerated pitting corrosion test of 304 stainless steel using ASTM G48; Experimental investigation and concomitant challenges

Marine and offshore structures constructed with stainless steel are regarded as having high corrosion resistance due to their superior self-passivating properties. However, they are equally susceptible to environmental degradation, especially due to pitting corrosion in highly corrosive marine environments. Pitting immersion tests performed on 304 austenitic stainless steel specimens using ASTM G48 presented significant challenges. Some of the issues encountered during these tests included unspecified experimental factors that control the pitting process such as pH, specimen size limitations, materials' properties, and the variation on the quality of the test solution. To overcome these challenges, the effect of surface finishes and aeration of the test solution on the corrosion behavior of 304 stainless steel specimens in 6% ferric chloride were examined and compared. The result shows that an aerated solution has much lower concentrations of pits compared to quiescent solutions. Controlled aeration eliminates unwanted crevice corrosion background noise. Subsequently, to suit larger specimens, the ASTM G48 was modified. This study presents the modified ASTM G48 procedure. A series of pitting corrosion tests on stainless steel specimen with different thickness were conducted and data were statistically evaluated. The generalized extreme value distribution, such as Weibull, provides adequate statistical descriptions of the pit depth and pit diameter distributions. The modified ASTM G48 offered advantages in the extraction and interpretation of the data for pit characteristics in the accelerated pitting corrosion test simulating actual marine environment.