About the Correlation between Crude Oil Corrosiveness and Results from Corrosion Monitoring in an Oil Refinery

Corrosion monitoring is an important tool to control and predict corrosion in piping, vessels, furnace tubes, etc. of chemical plants. This study shows results from ultrasonic wall thickness measurements in crude oil and high vacuum distillation units of a German crude oil refinery. Wireless ultrasonic sensors were installed on the external surface of selected piping to continuously monitor internal corrosion. The focus was on high-temperature corrosion (>220°C), which is mainly caused by sulfur and acid components that are present in crude oil and its fractions. Two corrosion parameters were calculated: corrosion rates (from wall thickness over time) and the change in shape of the ultrasonic back wall reflection over time (PSI). This latter parameter is derived from the ultrasonic waveform measured by each sensor. Both corrosion parameters showed different results regarding corrosion activity over time. This was explained by variations in process temperature that significantly influence wall thickness readings but not PSI. Furthermore, only limited correlation was found between corrosion and flow velocity/internal pressure. Finally, three crude parameters (total sulfur content, total acid number, and mercaptan content) were obtained from crude run history and compared to measuring data. Significant correlations between shape change and crude parameters were found, dependent upon sensor location/corrosion loop.