Numerical Simulation of Multiphase-Flow Enhanced Erosion-Corrosion Problems, 20-R8088Printer Friendly Version
Inclusive Dates: 01/01/09 Current
Background - Fluid flow significantly affects corrosion rate by causing accelerated mass transfer of reactants and corrosion products at boundary surfaces. Additionally, it affects the water chemistry and reaction pattern between dissolved species that influences surface corrosion. Similarly, the erosion process can be influenced by fluid velocity, shear, turbulence, and discrete phase properties and parameters such as impact velocity and angle. The combined effect of the erosion-corrosion process is greater compared to each individual process acting independently. Flow-enhanced erosion-corrosion problems are encountered in almost every engineered and natural system, which often results in costly downtime or aggressive maintenance requirement. The present work focuses mostly on erosion-corrosion problems encountered in nuclear power plants. Though the flow-induced erosion-corrosion problems can affect the primary coolant flow inside the containment structure, the proposed research specifically addresses the problems for the secondary side of nuclear power plants, where the majority of incidents and accidents related to flow-assisted corrosion has been encountered. Modeling of the erosion-corrosion process is highly challenging because it could be affected by a large number of flow parameters that are difficult to control and quantify simultaneously. Existing system level tools are currently used to predict erosion-corrosion processes based on thermodynamic and simplified flow conditions, using empirical correlations. The objective of the present study is to develop a methodology to calculate wall thinning in critical flow components by coupling the erosion and corrosion processes that dynamically account for water chemistry, corrosion kinetics, concentration and momentum boundary layer variations for realistic geometries.
Approach - In the current study, the flow field and particle motions are determined using a commercial computational fluid dynamics package, ANSYS-FLUENT. Initially, the flow modeling simulates a multicomponent continuous phase that includes water and a dissolved gas. The continuous phase also accounts for water chemistry that dictates the distribution of dissolved corrosive species. The discrete phase simulation simulates the behavior of solid particles (i.e., sand or debris). The latter study helps to locate the particle impingement region and calculates related statistics (i.e., impingement angle and velocity). These variables are required for calculating erosion rates using experiment-based correlations. Corrosion calculations are carried out using the dissolved species boundary layer and mass transfer estimation assuming diffusion transport in the near wall region. Specialized water chemistry, corrosion kinetics, and erosion models are being implemented as customized field functions.
Accomplishments - A bend pipe section has been identified as the workbench for the current research because this configuration is regularly encountered in the secondary coolant circuits of nuclear power plants. Hydrodynamic simulations have been performed on this geometry with water and dissolved oxygen to understand the pattern of secondary flows and mass transfer boundary layers. Additionally, discrete solid phase sand particle trajectory calculations have been completed. Two different erosion models have been implemented and tested in the solver. Currently, project staff members are implementing the detailed chemistry and corrosion kinetics within the solver framework for a complete assessment of corrosion damage.