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 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 piping components. The knowledge of local flow effects can be useful for developing targeted inspection plans for piping components, predicting the location of the highest FAC rate for a given piping component, and determining what piping components should be replaced. A similar evaluation applies also to FAC in heat transfer equipment such as heat exchangers and steam generators. The objective of this paper is to examine the role of flow and mass transfer in bends under FAC conditions. Bends experience increased FAC rates compared to straight pipes, and are the most common components in piping systems. When the flow effects are dominant, the FAC rate is proportional to the mass flux of ferrous ions, which, in turn, is proportional to the mass transfer coefficient in the flowing water. The mass transfer coefficient describes the intensity of the transport of corrosion products (ferrous ions) from the oxide-water interface into the bulk water. Therefore, this parameter can be used for predicting the local distribution of the FAC rate. The current paper presents plant and laboratory evidence of the relationship between local mass transfer conditions and the FAC rate in bends. It 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 artefact measurements for short-radius and long radius bends are presented. The effect of the close proximity of two bends on FAC rate is also examined based on CANDU™ NPP inspection data and compared with literature data.

On the non-destructive measurement of local mass transfer using X-ray computed tomography

“…If this is not predicted or detected in planned outages, there is the danger of sudden rupture and failure of the piping system. FAC consists of electrochemical reactions at the metal-oxide interface, chemical erosion at the oxide layer and convective mass transfer of the ferrous ions from the oxide-water interface into the bulk flow [1]. The mass transfer rate from the wall to the bulk flow plays a limiting role in the wall thinning rates.…”

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.…”

Low frequency axisymmetric longitudinal guided waves in eccentric annular cylinders

“…The FAC process, thus, also leads to pipe eccentricity over an extended axial region. [4][5][6] Noting that any wall thinning will cause an induced pipe eccentricity, this paper studies the feasibility of using ultrasonic guided waves to rapidly inspect tubes and pipes for possible eccentricity. Ultrasonic guided waves are attractive for this purpose as they offer the potential for screening and remote inspection from a single transducer position.…”