Corrosion Prediction Model of Submarine Mixed Pipeline X65 Steel under a CO2/Cl- Synergistic System

Submarine pipeline failures may cause incalculable consequences for the environment and human health. Most of hidden dangers leading to hazardous pipeline accidents (about 25%) are caused by CO2 corrosion. Although the operation of submarine mixed pipeline transport was started back in 2014, CO2 corrosion risk data still have not been reported. In this study, an autoclave for corrosion testing was applied to examine the effects of CO2 partial pressure, temperature, medium velocity, and Cl- concentration on the corrosion rate of the target pipeline. A preliminary analysis of four typical carbon dioxide corrosion rates, which are based on acquired experimental data and involve industrially accepted Norsok M506, De Waard 95, Cassandra (BP), and DWM corrosion models, respectively, revealed that none of these models are suitable for corrosion tests of pipelines. In this regard, a special model for the prediction and correction of the carbon dioxide corrosion rate was proposed on the basis of a multivariate regression method. The maximum error of the modified internal corrosion model was found to not be greater than 7%, which was 3226 times less than that of the Norsok M506 corrosion model.