Characterisation of soil/pipe interface at a pipeline failure after 36 years of service under impressed current cathodic protection

Abstract

Study on corrosion behaviour of buried pipeline in saline soil is presented, the pipeline is protected by coating and impressed current cathodic protection system. In this work, spectrometric and spectroscopic techniques were used to characterise the pipe/coating/soil interfaces. The results show the coating/pipe interface forms corrosion products including the following phases: magnetite, goethite, akaganeite and hematite. However, the main phases found at coating/soil interface are magnetite and ferric ion. The behavior is consistent with the corrosion of carbon steel in soil with oxygen and chloride ion. The reaction paths are proposed under the conditions of deteriorated coating, cathodic protection, saline soil and seasonal fluctuations.

Analysis of the Physicochemical, Mechanical, and Electrochemical Parameters and Their Impact on the Internal and External SCC of Carbon Steel Pipelines

“…The purpose of the coating is to prevent the corrosion and avoid the direct contact between the carbon steel surface and the external variables containing hydrogen to promoting SCC [ 1 , 4 , 5 , 17 , 24 ]. The type of coating that is applied commonly on external surfaces of the operating pipelines are epoxy, wax, polyolefin resin coating, coal, cement, composites, or alkyd, such as fusion bonded epoxy (FBE), liquid epoxy, urethane, asphalt, coal tar, multilayer or composite coating, poly(methyl methacrylate) PMMA, asphaltic compounds, polyethylene (PE), viscoelastic (plasticity of coating used) polymer, among other [ 1 , 3 , 5 , 7 , 9 , 10 , 120 , 121 , 122 , 123 , 124 ]. They are applied to protect the external pipeline with good mechanical properties, poor permeability to water, effective electrical insulation, good adhesion, adequate thickness, and high resistance to degradation with time [ 1 ].…”

“…For that reason, random modifications of the mechanical properties, ion concentrations of the soil, and electrochemical responses on pipeline steel-soil interface are expected. For geological purposes and scientific studies, it is important to mention that natural soils should be collected at the bottom of a buried pipeline (around 1.2 m in depth) from a right of way (ROW) where severe external corrosion damage could be identified [ 10 ]. Romanoff [ 168 ] has mentioned that the external corrosion for metallic structures is affected by metal types in the absence and in the presence of coating immersed in different soils located through the United States.…”

“…In empirical and theoretical practices, corrosion damage modeling and the effect of several field scenarios are related to SCC analysis, where the operating pipelines exposed to different external variables (types of electrolytes, temperature, pH, among other data) have been studied and reported in the literature [ 20 , 168 , 183 , 184 , 185 , 186 , 187 , 188 ]. Nowadays, SCC of carbon steel pipelines is increasing in popularity, and the original mechanical properties of the steels and their initial electrochemical interactions with natural soils, representative soil solutions, or any solution promoting cracking have been described including SCC, intergranular-SCC (IG-SCC), transgranular-SCC (TG-SCC), SSC, HIC, hydrogen embrittlement from testing and characterization of carbon steels in hydrogen or sour testing [ 8 , 9 , 10 , 11 , 189 ]. In this way, metallurgy, physicochemical properties, codes, mathematical models, and electrochemical responses to predict external corrosion in terms of pH value, redox potential, resistivity, and pipe-soil potential can be considered [ 184 , 185 , 186 , 190 ].…”

Electrochemical study of the corrosion rate of API steels in clay soils

“…Thus, variations of soil moisture and temperature in the environment may be a cause of the operational problems regarding the cathodic protections systems of the onshore pipelines, because it is not possible to control the temperature, effect and water content within the soil in a right of way (ROW). In addition, indirectly, the plant growth, microbial activity and soil structure, with the consequence that minerals present in the internal structure of the soil are dissolved, forming ions and solid solutions that can damage the coating and affect the corrosion process of pipelines (Quej-Aké et al , 2015). Moreover, evaporation of water increases the concentration of active species with formation of an ionic conductor.…”

Remote Monitoring System Design and Implementation for Impressed Current Cathodic Protection

“…The principle of cathodic protection technology is to corrode the metal surface structure to provide a large number of electrons. The protected structure becomes the cathode, and the electron mobility of metal corrosion is inhibited, to avoid or diminish corrosion [1][2].…”