Investigation of corrosion behavior at elbow by array electrode and computational fluid dynamics simulation

Abstract

The present study focuses on the flow-accelerated corrosion (FAC) behavior of A106Gr.B steel at 90°elbow by electrochemical measurement and computational fluid dynamics (CFD) simulation. The FAC rates under turbulent flows with a velocity of 3 and 1.5 m/s were measured by an array electrode technique in a loop system. The experimental results reveal that the maximum FAC rate appears at the extrados of 90°elbow, consistent with the locations from the rupture of the carbon steel piping in the worst cases at elbows. In addition, an effective mass transfer coefficient in consideration of the geometric factor was used to evaluate the FAC rate at intrados and extrados of the 90°elbow by CFD simulation. The predicted results are in good agreement with the experimental values.

The Roles of Fluid Hydrodynamics, Mass Transfer, Rust Layer and Macro-Cell Current on Flow Accelerated Corrosion of Carbon Steel in Oxygen Containing Electrolyte

“…The macro-cell current is an important factor for steels subjected to an inhomogeneous flow condition. It is known that the inhomogeneous flow field usually occurs at the elbow, 3,21,23,28,31 reducer 12,30 and welded joint 18 of the pipeline and the surface of the ship hull or other large-scale steel structures, 17,34 which could lead to the non-uniform distribution of the local mass transfer rate and rust layer. Major anodic sites might concentrate at the local areas where lower mass transfer rate are registered.…”

“…It is generally found that the local areas where high FAC rates are registered are always coincide with the areas suffering high wall shear stresses or high mass transfer rates. 21,27,28,30 As a result, the study of localized FAC is well linked to the prediction of the local areas where high wall shear stress and high mass transfer rate are registered. However, Kitajima 33,34 claimed that serious FAC of the cast iron pumps preferred to occur at the local area around the shaft hole where the flow velocity and the wall shear stress were relatively low.…”

“…2,5 Due to the geometry changes of the steel structures, the distribution of the flow field around the steel surface is not always uniform. 3,11,21,22 The local mass transfer rates would be different on the steel interface under inhomogeneous flow fields, [23][24][25][26] leading to the non-uniform propagation of FAC on the steel interface. The influences of the fluid hydrodynamics on the local FAC performance were well studied in previous researches 21,[27][28][29][30][31][32] using multi-electrode array technique in conjunction with computational fluid dynamics (CFD) simulation.…”

“…3,11,21,22 The local mass transfer rates would be different on the steel interface under inhomogeneous flow fields, [23][24][25][26] leading to the non-uniform propagation of FAC on the steel interface. The influences of the fluid hydrodynamics on the local FAC performance were well studied in previous researches 21,[27][28][29][30][31][32] using multi-electrode array technique in conjunction with computational fluid dynamics (CFD) simulation. The localized FAC behaviors could be probed by the electrodes which are arranged at different locations of the steel structure.…”

“…15,37 However, a porous rust layer might enhance the local cathodic reaction in some cases, leading to the acceleration of FAC. 41 It is found from previous studies [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15]21,30,33,34,41 that the propagation of FAC is relatively complex which is significantly influenced by the fluid hydrodynamics, mass transfer rate, rust layer and macrocell current. In order to figure out the interaction and the influences of these factors on FAC in oxygen containing electrolyte, the nonuniform FAC performances of the EH 36 carbon steel is investigated beneath a jet rig.…”