This paper presents the case history of corrosion experienced on a new atmospheric and vacuum crude distillation unit The crude charged was a low sulfur type, averaging 0.20% sulfur content, which is produced in West Texas, mostly from Ellenburger formations, of Ordovician age. Some test data for this crude, which are applicable to the corrosion problems, are tabulated for comparative purposes with like data for other crudes. A simplified flow diagram of the unit shows temperature and pressure conditions. The materials used in the various items of equipment are given.
Most affected by corrosion were the atmospheric tower overhead condenser shells and the carbon steel tubes in the radiant section of the fired heater where desalted crude is heated to 600° F. The paper deals principally with the nature of the corrosion in the furnace tubes, the factors entering into the problem and remedial measures used. Ammonia injection was used in neutralizing the corrosive elements present in the atmospheric tower overhead steam and 7% chro-mium-0.5% molybdenum alloy steel tubes were substituted for carbon steel in the radiant section of the furnace. Corrosion rates for the carbon steel heater tubes are plotted vs. temperature and compared to those experienced when processing West Texas crude containing 1.5% sulfur. The marked effects which the tube wall temperatures have on the corrosion rates are discussed. A peculiar feature about this corrosion experience is that the same crude which gave trouble on the new unit had been processed previously in an older, though similar, unit for approximately three years without corrosion difficulties. A comparison between operating data for the two units is made.
