Relationship between in-situ measurement of soil parameters and metal loss volume of X70 carbon steel coupon

Abstract

Corrosion in soil environments is a serious threat to underground metallic structures such as oil and gas pipelines, waste containers and pilings. This study investigates the relationship between in-situ soil parameters and metal loss of X70 carbon steel. A total of 207 carbon steel coupons of X70 were installed underground at five sites for 18 months and have been retrieved every 3 months to measure the metal loss as a function of time. This study focused on in-situ corrosion parameters, namely, soil resistivity (Res), pH, moisture content (Mc) and chloride content (CI). The results of corrosion metal loss and in-situ parameters were analyzed using statistical methods to obtain the relationship of the studied p arameters to metal loss. Extreme data were removed through proper outlier's detection technique: Box plot, Dixon test and t-test. Corrosion test were then carried out to examine the relationship between in-situ measurement of soil parameters and metal loss. The results indicated that Mc, CI and Res were found to be the most influential variables on the observed metal loss. An increase in Mc and CI is likely to promote corrosion growth whereas higher resistivity will reduce the corrosion risk. Nevertheless, pH was found to be relatively insignificant to the corrosion process.