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10360 Description and Explanation of an FCC Overhead System Unexpected Corrosion

Case study: A leak occurred in a Fluid Catalytic Cracking unit main fractionator overhead line elbow in June 2006. Following this leak, investigations showed acidic corrosion-erosion in the overhead circuit. This type of corrosion was unexpected in this circuit.

Product Number: 51300-10360-SG
ISBN: 10360 2010 CP
Author: Matthieu Devallée
Publication Date: 2010
Industry: Petroleum Refining
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A leak occurred in a FCC unit main fractionator overhead line elbow in June 2006. Following this leak, investigations showed acidic corrosion-erosion in the overhead circuit. This type of corrosion was unexpected in this circuit.

Process water analysis revealed that during normal process operations, acidic corrosion was not possible. 2002-2006 unit run analysis highlighted the fact that this unit has been frequently in a transient phase called catalyst recirculation. Water sampled during those periods exhibited a very low pH due to the presence of sulfuric acid. During catalyst recirculation operation sulfur trioxide is formed. SO3 goes up in the main fractionator overhead and condenses as H2SO4 with the water vapor. This media has corroded carbon steel equipments located after the water dew point. A way to mitigate this corrosion is a condensed water pH control during those periods. This paper covers the description and the explanation of this leak.

Keyword: Refining, Corrosion Failure, FCC unit, Acidic dew point corrosion, Sulfuric acid corrosion

A leak occurred in a FCC unit main fractionator overhead line elbow in June 2006. Following this leak, investigations showed acidic corrosion-erosion in the overhead circuit. This type of corrosion was unexpected in this circuit.

Process water analysis revealed that during normal process operations, acidic corrosion was not possible. 2002-2006 unit run analysis highlighted the fact that this unit has been frequently in a transient phase called catalyst recirculation. Water sampled during those periods exhibited a very low pH due to the presence of sulfuric acid. During catalyst recirculation operation sulfur trioxide is formed. SO3 goes up in the main fractionator overhead and condenses as H2SO4 with the water vapor. This media has corroded carbon steel equipments located after the water dew point. A way to mitigate this corrosion is a condensed water pH control during those periods. This paper covers the description and the explanation of this leak.

Keyword: Refining, Corrosion Failure, FCC unit, Acidic dew point corrosion, Sulfuric acid corrosion

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