Cathodic protection of soil buried steel pipelines - a critical discussion of protection criteria and threshold values

Abstract

This paper represents the consensus reached during a panel discussion held at the CEOCOR International Congress in Stockholm, Sweden, June 2–5, 2015. It reviews the state‐of‐the‐art about the generally accepted understanding of the working mechanism of cathodic protection of ground buried steel structures. Based on this, limitations of existing protection criteria are discussed, particularly the difficulties related to measuring and interpreting current‐applied potentials, instant‐off potentials, and IR‐free potentials. A set of protection criteria and their interpretation in accordance with the understanding of the working mechanism of cathodic protection is proposed. The main idea is that it is distinguished between the following two situations: 1) conditions that permit an increase in pH at the steel surface as a result of the applied protection current (good bedding conditions inhibiting convection) and thus provide corrosion protection by achieving passivity; and 2) situations where this is not possible (e.g. in streaming soft water) or where it is unknown if this is possible, and thus effective corrosion protection can only be achieved by polarizing the steel into the immunity zone.

Monitoring pH in corrosion engineering by means of thermally produced iridium oxide electrodes

“…In laboratory studies, it has been shown that relatively low protection current densities lead to a significant increase in pH at the steel surface . Only a few mA/m 2 appear to be sufficient to raise the pH at the steel surface to values above 10 and provide effective cathodic protection.…”

“…They are small, work well in the relevant range of pH (>9), and have response times that are sufficiently fast for the application in CP studies in soil. Considering the long‐standing controversy about CP criteria based on potentials, being able to measure the pH in situ in the soil would contribute to resolving open questions in research and practice.…”

Effects of metabolic activity of sulphate‐reducing bacteria on heterogeneous corrosion behaviors of copper in seawater

“…Therefore, metabolic activity of SRB is high in exponential phase and stationary phase, and low in death phase during SRB growth cycle. In the most of SRB induced corrosion cases, heterogeneous corrosion is the typical corrosion form, and it is influenced by absorption of biofilm, corrosive metabolic products, and SRB cells . However, little is known about the relationship between metabolic activity of SRB and heterogeneous corrosion of metal during SRB growing process.…”

Protection cathodique appliquée au béton armé aérien : étude expérimentale et modélisation

“…Il est important de noter que la communauté de la Protection Cathodique du secteur Terre, travaillant dans le domaine des structures métalliques enterrées, est consciente depuis des décennies de l'hétérogénéité du champ de potentiel en présence de corrosion par macro-piles [27].…”