Numerical modeling of corrosion and design of cathodic protection systems
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Date
2024-06-25
Authors
Καλοβελώνης, Δημήτριος
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Abstract
Corrosion is major threat for structures in all sectors, such as energy, oil and gas, transportation, chemistry, civil engineering, pharmaceuticals, machinery etc. Corrosion threatens the structural integrity of offshore structures, steel reinforcement, pipelines transporting water and hydrocarbons, chemical plants, power plants and nuclear reactors etc. Corrosion forms are divided in two main categories, depending on the damage they cause; (a) generalized corrosion, which occurs on the whole surface in contact with the electrolyte and (b) localized corrosion. Localized corrosion occurs due to non-homogeneous conditions either on the metal or the electrolyte composition. Forms of localized corrosion are the galvanic corrosion, pitting corrosion, crevice corrosion, stray current corrosion etc. Currently, the economic factor is a very important motivation for much of the current research in corrosion. A recent study by NACE estimates the global cost of corrosion to be US$2.5 trillion. The use of corrosion prevention and protection methods such as corrosion inhibitor injection, selecting corrosion resistant materials and cathodic protection, can reduce the corrosion cost by 15-35%. Several methodologies for corrosion prevention and protection have been used in the industry, such as corrosion inhibitors, coating systems, corrosion resistant materials selection, cathodic protection etc. According to standards (e.g. ISO 15589, ISO 24656, DNV RP-0416) cathodic protection is mandatory for the submerged surfaces of offshore structures and ships, aboveground tank bottoms, and buried pipeline networks. Cathodic protection systems are divided in two categories (a) impressed current cathodic protection (ICCP) s and (b) sacrificial anode cathodic protection (SACP) systems. Standards (e.g. ISO 15589, ISO 24656, DNV RP-0416) recommend that ICCP design should be carried out using numerical simulations, while SACP design is carried out using the Ohm’s and Faraday laws. Furthermore, if form the resulting design anode interference may occur, standards recommend the use of numerical simulation to carry out the SACP design. Although, the first developed model was a finite differences (FD) scheme one, BEM is used extensively the past 40 years, due to the advantages it offers, in comparison with the finite element method (FEM), and finite volume method (FVM). More precisely, BEM offers the advantages of high solution accuracy, especially in the computation of potential gradients (current density), as well as reducing the problem dimensionality by one. The latter advantage is very pronounced, especially for infinite and semi-infinite electrolytes, since only the boundary surfaces must be discretized. The aim the present work is to study, galvanic, macro-cell, and stray current induced corrosion problems, in order to design effective cathodic protection systems, that protect structures from corrosion and extend their service life, utilizing computational methods. To this end boundary element methods are developed. More precisely, a local domain BEM has been developed to solve corrosion problems, and the ACA/BEM has been extended for solving galvanic, macro-cell, and stray current induced corrosion, and cathodic protection problems of large-scale structures. Then the above-described methods are utilized to design effective cathodic protection systems.
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Keywords
Corrosion, Corrosion protection, Corrosion prevention, Cathodic protection, Cathodic protection design, Galvanic corrosion, Macro-cell corrosion, Stray current induced corrosion, Localized corrosion, Cathodic protection systems interference, Optimal design, Boundary element method