Multi-Factorial Prediction of Mild Steel Exposure Time during Its Corrosion Inhibitionwith Hibiscus Sabdariffa Leaf Extract in 0.5M H2SO4

Abstract

This paper evaluates the exposure time of mild steel (which corroded in sulphur acid solution while in contact with an inhibitor- Hibiscus Sabdriffa) based on pre-determined penetration depth and corrosion rate. The analysis carried out was using a derived empirical model; θ = exp(Ϧ(ẟγξ^-1) - ẞ). Mild steel was submerged in 0.5M H₂SO₄ containing sabdariffa leaf extract which serves to inhibit corrosion of the steel. In the course of the model derivation, following experimentals, the applied range of values of the process parameters: exposure time, penetration depth and corrosion rate were 0.00548 – 0.011 hrs, 0.0047 – 1.0121mm, 0.8638-0.1027mm/yr respectively. The validity of the model is strongly rooted on the core model structure; lnθ + ẞ ≈ Ϧ(ẟγξ^-1). The model-predicted results agree with previous research on the direct relationship between the corrosion rate & penetration rate and exposure time, while inhibitor concentration is constant. The standard error incurred in predicting the model based exposure time relative to the experimental results was 0.0004%, implying over 99% model confidence level. The exposure times per unit penetration depth and corrosion rate for experimental & model-predicted results were evaluated as: 0.7459 & 0.9297 yr mm^-1 and 0.0231 & 0.0288 (yr)² mm^-1 respectively. Furthermore, the correlations between these highlighted parameters, as evaluated from both results were all > 0.97. The overall maximum deviation of model-predicted mild steel exposure time from experimental results was 9.09%.