Response Evaluation of Mild Steel Corrosion Rate in H2SO4 to the Synegistic Influenceof Exposure Time and Steel Weight Loss

Abstract

The response of mild steel corrosion rate in 0.5M H₂SO₄ (while in contact with an indicator- Hibiscus Sabdariffa) to the synergistic influence of exposure time and weight loss of the steel has been successfully evaluated. The predictive evaluation was carried out using a derived empirical model;

                                          ξ  =  Ϧ (- ẞɤ² + Ҽɤ - Nτ² + Фτ+ Ǧ) 

Prior to derivation of the empirical model, mild steel was submerged in 0.5M H₂SO₄ containing an inhibitor; sabdariffa leaf extract which strived to resist corrosion of the steel. In the course of the model derivation, applied ranges of values of the process parameters: corrosion rate, exposure time and weight loss were 0.6916 – 0.7086 mm/yr, 0.00548 – 0.0164yr and 0.0799 -0.2456g respectively. Results generated were based on weight-loss method. The validity of the derived model is strongly rooted on the core model structure; (ξ/Ϧ) – Ǧ ≈ - ẞɤ² + Ҽɤ - Nτ² + Фτ_.. The model-predicted results agree with previous research on the polynomial relationship between the corrosion rate and exposure time & mild steel weight loss, while inhibitor concentration is constant. The standard error associating model prediction of corrosion rate, relative to the experimental results was 0.0076%, implying over 99% model confidence level. The corrosion penetration depth on the mild steel  per unit exposure time for experimental & model-predicted results were evaluated as: 4.406 x 10^-4 mm and 4.509 x 10^-4 mm, while corrosion rate per unit weight loss of the steel were 1.304 and 1.335mm/yr/g respectively. Evaluated correlations between corrosion rate and exposure time & weight loss of steel, as obtained from both results were all > 0.96. Deviational and statistical analyses of evaluated results indicate that the overall maximum discrepancy of model-predicted mild steel corrosion rate from experimental results was 2.4%.