Negritashmy Convection coils in fired heaters are susceptible for external corrosion due to condensing vapor deposits of flue gas (circulation) from fired heater burners. This happens when there is a crash shut down of the furnace heaters or upset conditions in the down stream equipment of if heat transfer in the convection zone is affected due to blockage or due to vapor / salt deposits from circulating vapors at the top zones. If the convection zone tubes are finned, from better heat transfer, then fins become the first casualty for external corrosion. Localized external corrosion may also occur at the bends of convection zone coils in these fired heaters. Another possibility is : localized corrosion due to poor heat transfer conditions and flue gas or steam-vapor reaction at the internals of some coils. Access for good inspection of covnection zone coil tubing is a problem (to assess the damage). Comparatively, radiant coils in the same furnace heaters will have better access. Radiant coils can easily be replaced in segments - even if the tubes are affected due to internal corrosion or external corrosion (caused by fuel oil / fuel oil or asphalt fired burners). It looks like : Asphalt fired heaters would be more susceptible for external corrosion compared to fuel oil or fuel gas from longivity of tube failure in convection zone - due to localzied corrosion (external corrosion). Trust this is of help to you C.V.Srinivasan Nishi Engineers Pvt Ltd India June 2, 2006 E-mail: nishi@vsnl.com >Recently we experienced some localized corrosion problems in >the convection section of our crude distilling unit furnace. >This problem caused failure of some tube. >Can anyone provide me with information on typical corrosion >problems experienced in convection section of heaters during >operation or idlle time? We normally fire asphalt, fueloil >or fuelgas in this heater.

Srinivasan and Krish Thanks for your reply. The problem experienced is due to external corrosion. The corrosion is in form of localized pitting. The 2 failed tubes were perforated in the corner where the tubes lean against the refractory. We can not assure the condition of the other tubes in the convection bank due to the limited inspection possibility. At first we considered H2SO4 corrosion during iddle time, but the average iddle time in the last 30 years has been around 300 days. So there would give us a corrosion rate of almost 6mm/year at with a lot of assumptions. We have had some crash shut down in the past but I do not know in how much this can accelerate the corrosion of this tubes. Is this possible or is there an other failure method that can cause this kind of demage on the tubes.