Comparison of Percentage Weight Loss and Corrosion Rate Trends in Different Metal Coupons from two Soil Environments

Abstract

Average percentage weight loss (APWL) and corrosion rate (CR) were determined for mild steel (MS), carbon steel (CS) and stainless steel (SS) strip coupons buried in a water-logged soil (WL) and a sandy soil (SD)for a period of 190 days. Post-exposure analyses of the coupons over the entire period showed that the APWL for the MS coupons retrieved from the water-logged soil and sandy soil sites were 5.4% and 2.8%, respectively. The corresponding CRs were 5.58 mpy and 3.18 mpy, respectively. Similarly, APWL for the CS coupons from the water-logged soil and sandy soil sites were 4.5% and 3.6%, respectively while their CRs were 3.51 mpy and 3.67 mpy, respectively. For the SS coupon, APWL and CR were 0.12% and 0.32 mpy, respectively from the water-logged soil and, 0.08% and 0.19 mpy, respectively for the sandy soil site. It was observed that generally, there was an inverse trend between weight loss and corrosion rates in the coupons as the exposure period increased such that, while APWL values were seen to be increasing, CR values were decreasing. This trend was observed in all three coupons and at both sites, except for a few excursions which did not significantly affect the established trend. It was observed that APWL increased by nearly the same ratio that CR decreased during the period of exposure of the coupons.