Flow and Mass Transfer in Bends Under Flow-Accelerated Corrosion Wall Thinning Conditions

Abstract

The three groups of parameters that affect flow-accelerated corrosion (FAC) are the flow conditions, water chemistry, and materials. Nuclear power plant (NPP) data and laboratory tests confirm that, under alkaline water chemistry, there is a close relationship between local flow conditions and FAC rates in the piping components. The knowledge of the local flow effects can be useful for developing targeted inspection plans for piping components and predicting the location of the highest FAC rate for a given piping component. A similar evaluation applies also to the FAC in heat transfer equipments such as heat exchangers and steam generators. The objective of this paper is to examine the role of the flow and mass transfer in bends under alkaline FAC conditions. Bends experience increased FAC rates compared with straight pipes, and are the most common components in piping systems. This study presents numerical simulations of the mass transfer of ferrous ions and experimental results of the FAC rate in bends. It also shows correlations for mass transfer coefficients in bends and reviews the most important flow parameters affecting the mass transfer coefficient. The role of bend geometry and, in particular, the short and long radii, surface roughness, wall shear stress, and local turbulence, is discussed. Computational fluid dynamics calculations and plant artifact measurements for short- and long-radius bends are presented. The effect of the close proximity of the two bends on the FAC rate is also examined based on CANDU (CANDU is a registered trademark of the Atomic Energy of Canada Limited) NPP inspection data and compared with literature data.

A Numerical Study on Flow-Accelerated Corrosion in Two Adjacent Elbows

“…3 presents the results of MTC distribution for the first elbow and the second elbow (i.e., upward direction). From the previous studies [4][5][6] , the results of Chilton and Colburn analogy are in good agreement with the measured wall thickness. FAC susceptible locations in the corresponding components can be found from the MTC distribution results.…”

Numerical study of the hydrodynamic parameters influencing internal corrosion in pipelines for different elbow flow configurations

“…When these corrosive solutions come into contact with the internal surfaces of pipelines, a strong electrochemical reaction takes place which can result in severe internal corrosion over time (Nešić, 2007;Zhang, Wang, Wang, & Han, 2012). A large number of numerical simulations and experimental studies have been carried out in order to better understand the mechanism of wall thinning and other problems within pipelines related to corrosion, and it has been proposed that the wall shear stress and mass transfer coefficient can be used to predict where corrosion in pipelines due to erosion will occur (Hu & Cheng, 2016;Pietralik & Schefski, 2009;Pietralik & Smith, 2006;Utanohara & Murase, 2019;Zhang, Zeng, Huang, & Guo, 2013;Zheng & Che, 2006). A summary of previous studies conducted on pipelines with diameters ranging from 14 to 105 mm which use the wall shear stress and mass transfer coefficient hydrodynamic parameters for predicting the corrosion process is presented in Table 1.…”

Numerical Modeling of Flow and Mass Transfer Effect on Flow-Accelerated Corrosion in Consecutive Elbows

“…Enhancement factors for single components are available for FAC prediction codes; however, these codes do not include the effect of components in close proximity to each other. Therefore, the results can provide inaccurate predictions of FAC rates when flow through an upstream component affects the downstream component [2].…”

“…This complex flow pattern significantly affects the local shear stress and mass transfer distribution at the pipe wall. FAC in a single elbow has been studied previously [2,3]; however, there are limited data available for FAC in 2 consecutive elbows [4,5]. Experiments have been conducted recently at McMaster University [6][7][8][9][10], using the dissolution technique, to quantify wall thinning rates under single-phase flow conditions for 3 arrangements of 2 consecutive elbows, as shown in Figure 1: (i) in-plane S-configuration; (ii) in-plane C-configuration; and (iii) outof-plane configuration.…”