Corrosion rates of up to 0.8 mm/per month were detected on a Visbreaker fractionation column.
Internal examination of the column showed that the shell corrosion was confined to the vicinity of four
trays situated approximately two thirds of the way up the column, with the highest rates being seen
within the downcomers. Examination of the corroded areas within the downcomers indicated the
presence of smooth, uniform zones of metal loss characteristic of organic acid corrosion. Further
analyses of both the internal deposits and sections of shell plate taken from the areas of high corrosion
indicated that organic acids were present. While the column was on-line, hydrogen flux measurements
were recorded in the areas of active corrosion in order to provide an estimate of the corrosion rate in
real time, to monitor the extent of active corrosion, to determine the probable cause of corrosion and to
assess the effectiveness of a newly-initiated corrosion inhibitor program. The corrosion rate
estimations were found to correlate well with ultrasonic thickness measurements. Hydrogen flux
measurements also confirmed that the injection of a filming amine inhibitor was effective in reducing the
corrosion rate of the affected area by 10-fold, despite the high temperature of up to 220°C.
Keywords: Naphthenic Acid, Visbreaker, Hydrogen Flux, Corrosion Inhibitor, TAN, Soaker Severity,
High-Severity