Correlation of hydrogen flux and corrosion rate measurements carried out during a severe episode of corrosion-erosion attributable to naphthenic acid

Over a six month period, UT measurements at a matrix of measurement sites on a Fractionation column indicated that it was suffering from severe internal corrosion.  It was decided to monitor hydrogen flux at all measurement points on a frequent basis.  The resulting flux profiles broadly cotrended.  Time averaged flux and longer term corrosion rates correlated well.  In a more sophisticated treatment, flux data was converted into hydrogen activity at the corroding face, to compensate for hydrogen permeation through the steel, thus normalising any variations in steel temperature and thickness.  Again the correlation of activity and shorter term corrosion rate was good, with a correlation factor that was closely comparable to that obtained from laboratory data.  In short, the data illustrates that, at temperatures where naphthenic acid corrosion can take place, hydrogen flux may provide a keen indication of the corrosion rate in near real time, with the diffusive delay in flux stabilisation upon a corrosive change typically being one hour.