CFX study of flow accelerated corrosion via mass transfer coefficient calculation in a double elbow

• Mass transfer coefficient (MTC) was studied on the wall of a double elbow pipe.
• The effect of the flow velocity and the distance between two elbows were studied.
• By increasing the flow mean velocity, MTC increases.
• The maximum MTC was occurred in the intrados of second elbow.
• The geometrical factor and the close proximity of two elbows were investigated.

Using CFX numerical simulation, this study aims at calculating Mass transfer coefficient (MTC) as a parameter that indicate the FAC rate on the wall of the double elbow. A double elbow in the feeder water piping system of a typical combined cycle power plant that had been damaged due to the FAC was considered and was studied. In this study the influence of several parameters such as the mean flow velocity and the dimensionless distance between the two elbows (L/D) on the MTC at the elbows was investigated. The geometrical factor and the close proximity of two elbows with respect to the mass transfer coefficient were studied.It is found that mass transfer coefficient increases by Reynolds number. The maximum MTC was occurred in the intrados of second elbow. It is found that there is a very good coincidence between the locus in which the maximum MTC was calculated and the locus in which minimum wall thickness was measured.It is observed that as the remoteness between the elbows (L/D) increases, the Close Proximity Effect (CPE) is decreasing for L/D < 7. As L/D gets amplified (L/D > 7) the CPE is increasing very slowly and became constant. This CPE value is lower in comparison with that of L/D < 7. This is due to the fact that, when L/D > 7, the second bend experiences less impact due to the first bend and, also, there is a fully developed flow between both the bends.