Numerical modelling of buried pipelines under DC stray current corrosion

Yaping Zhang,Lianqing Yu,Xiao Tang,Chi-Man Lawrence Wu,Siu-Pang Ng,Qiong Feng

doi:10.5599/jese.567

Abstract

Corrosion of buried pipelines caused by stray currents is becoming a serious industrial and environmental problem. It is therefore necessary to study corrosion mechanisms of buried pipelines under DC stray currents in order to propose effective anti-corrosion measures. Since measurement of the potential is one of important ways to identify stray current intensity, the COMSOL Multiphysics software was used to simulate stray current corrosion dynamics of buried pipelines. It was also used to calculate the distribution and intensity changes of electrolyte potential in the cathodic protected system by solving Laplace’s three-dimensional equation. The obtained results showed that increased applied voltage leads to more positive shift of a pipeline potential, resulting in acceleration of stray current corrosion. On the contrary, increased soil resistivity can retard the corrosion process. The protected pipeline with a sacrificial anode suffers less corrosion interference than unprotected pipeline. Two crossed arrangement of pipelines makes no difference in corrosion of protected pipeline, but affects greatly on unprotected pipeline.

Highlights

Stray currents arising from railway systems can induce corrosion of buried pipeline structures and result in severe damage [1]
Because there is potential gradient surrounding the anode, anode will interfere with the current flow path, that is, protected pipeline can accept current near the anode and leading to current flowing along the pipeline
Two different arrangements of protected and unprotected pipelines were studied, and potential distributions of buried pipelines were for both arrangements obtained by simulations

Summary

Introduction

Stray currents arising from railway systems can induce corrosion of buried pipeline structures and result in severe damage [1]. A routine way to mitigate the SCC of pipelines is to install sacrificial anodes or apply a current to inappropriate bedding for protected structures. There are three kinds of numerical analysis for cathodic protection systems, including finite difference method, boundary element method and finitude method Among these methods, the boundary element is suited to off-shore structures as a method capable to infer the distribution of potential and current densities along the metallic structure/electrolyte interface [7]. Models were built up to simulate the corrosion of the protected/unprotected structure due to stray currents. Sacrificial anode protection is equivalent to a direct current flowing to the pipeline compulsively, resulting in negative potential shift and reducing the corrosion rate of the structure. Value 96485 C/mol -0.76 V 7.1×10-5 A/m2 0.41 mV/decade -1.03 V 0.11 A/m2 0.15 mV/decade 0.189 V 7.7×10-7 A/m2 -0.18 mV/decade 5×10-4 m -0.9 V

Results and discussions

10 V 15 V 20 V 25 V

Conclusions