Assessment by finite element modeling of corrosion in dent on X52 steel pipelines

Abstract

While corrosion in dent presents a realistic threat to integrity of pipelines, there have been limited methods available to assess the problem and its effect on fitness-for-service of the pipelines. In this work, a method was developed to assess the corrosion in dent on an X52 steel pipe by considering both mechanical and electrochemical corrosion factors and their interaction at an unconstrained dent through finite element modeling. Parametric effects including dent depth, dent size (i.e., open mouth diameter for spherical dents) and internal pressure on distributions of stress, anodic current density and net current density were determined. The stress concentration at the dent accelerates corrosion due to a mechano-electrochemical interaction. As the dent depth increases, the local stress concentration is enhanced, resulting in increased corrosion activity and corrosion rate. The most negative corrosion potential and the maximum anodic current are located at the center of the dent, where the anodic reaction occurs. The cathodic reaction mainly occurs at the dent sides. The internal pressure has a limited effect on the anodic current density. The dent with a smaller open diameter can cause greater local stress concentration and anodic current density. At specific dent depths, small dents tend to accelerate local corrosion at a more rapid speed than bigger dents.