I would like to have the forum feed beck about de subject-wash oil corrosion We have had a breakage in a thermocouple in P5 that this installed at discharge line of wash oil recirculation pumps. The line is a side cut of accumulating column bottom tray that goes to a separator to free the light fractions; bottom fractions are refluxed to the column feed. The temperature of the circuit is of near 350ºC. After the inspection, the thermocouple displayed a homogenous corrosion by light pitting and great thinning. In the pursuit, we began a tight inspection by measurement of thickness in all the line, that of project has 6.35mm thickness, and in average registered thickness of 3.5mm, with some points of 1.6mm. After this, we were decided by substitution of the line and after his dismantling, we verified that its interior showed a rough surface with long and smooth pitting (naphtenic corrosion). Related with wash oil line, we have later inspected also the bottom line of the column, as well as light and heavy gas oil cuts. As result of this inspection, only the thermocouple of bottom line of the column, registered corrosion with loss of thickness and type, like the thermocouple in P5 that this installed in the compression line of the wash oil recirculation pumps. The flow velocity in the wash oil circuit with severe corrosion is about 3m/s. But what makes me thinking is the high homogeneous thinning on thermocouples installed at the bottom of vacuum column, at wash oil circuit and also at visbeak unit feed. These thermocouples are in A335 P5 material; homogeneous thinning is not typical of naphtenic corrosion. Because of velocity and high turbulence if, naphtenic crude was present, thermocouples should be points highly affected by hard pitting and wear, not by homogeneous thinning don’t you agree? We do not have a great experience with naphtenic crud oils, only a year ago we began to process them in small mix amounts. Alf and year ago we began to increase the processing of naphtenic crude oils such as kuito and merlin in mixes of near 20%. As son as we began with this practice we began to use corrosion inhibitor slate crude oils with TAN nºs varying from 0.3 to 0.6. We have inhibitor injection points in the load of vacuum heater and an other common point to light and heavy gas oil cuts coming from vacuum column. 48 hours before making the change of feed to naphtenic crud oil, we start a shock injection of an inhibitor in a rate of near 50ppm, than the maintenance injection rate is of 10ppm. We have on line corrosion probes by electrical resistance, we make analysis of TAN in the gas oil cuts and we analysed the relation Fe / Ni in the feed, in the bottom vacuum residuum and in the gasohol cuts. Recently we have processed crude with TAN 0.6 and down. Thank you for your empathy Best regards Luis Marques