Factorial Design based Optimisation of Crevice Corrosion for Type 304 Stainless Steel in Chloride Solutions

The effects of chloride concentration, creviced scaling factor and immersion time on the percentage area and maximum depth of attack for Type 304 stainless steel (SS304) in chloride solutions were investigated. The crevice assembly comprised of coupon (SS-304), polytetrafluoroethylene (crevice former) and fasteners (titanium bolt, nut and washers). The full immersion tests were based on ASTM G-78 using full factorial design to study the effects of chloride concentration (1.5, 3.0 and 4.5 w/w%), crevice scaling factor (8, 16 and 24) and immersion time (15, 30 and 45 days) on the percentage area of attack (Y₁) and maximum depth of attack (Y₂) of SS-304. Data obtained was used to develop and optimize the models of Y₁ and Y₂ in terms of the three factors using Response Surface Methodology (RSM). The R² of Y₁ and Y₂ were 0.98 and 0.91, respectively. The minimum Y₁ (5.63%) and Y₂ (3.32×10⁻⁷ mm) were obtained at 4.5% chloride concentration, 20 scaling factor and 15 days immersion time. The predicted optimal conditions agreed with the experimental results for validation with a maximum absolute relative error of 5.75%.