Analysis of Dew-Point Corrosion in Crude Fractionator Overhead Materials Using Advanced Corrosion Monitoring

Severe localized corrosion in crude unit overhead systems is a critical integrity concern, particularly under transient wetting conditions. This study combines high-frequency online ultrasonic (UT) monitoring with a simplified dew-point temperature margin (ΔT) to evaluate short-term changes in corrosion severity during operation. Wall-thickness data obtained at 12 h intervals were used to derive long-term thinning trends and a short-interval corrosion rate indicator (CR12h). CR12h increased as ΔT decreased, indicating that reduced dew-point margin was associated with increased corrosion severity. Although ΔT is not an exact thermodynamic dew-point prediction, it served as a practical operational proxy for transient wet-corrosion propensity. The evaluation supported partial replacement of the affected column-top region with Alloy C-276 cladding. Follow-up inspection after four years showed approximately 0.1 mm of pitting, corresponding to about 0.025 mm/y, which was approximately one order of magnitude lower than the previous Type 405 stainless-steel cladding. These results demonstrate a practical approach for linking continuous corrosion-monitoring data with operational indicators and material-selection decisions in crude unit overhead systems. The study further illustrates how monitoring-derived insights can be translated into repair planning and subsequently validated through long-term field performance following material upgrade.