Metallic structures in service in seawater are protected coupling cathodic protection and paints, where the former may induce disbondment of the latter. A preliminary evaluation of the cathodic disbondment risk can be made by cathodic disbondment tests, CDTs. Many CDTs use cathodic potentials as large as E < -1400 mV vs SCE applied up to 90 days. Only two CDT protocols require contemporary anode isolation, current and pH monitoring, without its correction. These three aspects were considered to develop a hybrid CDT; it consisted in polarizing steel panels at -1500 mV vs SCE for 12 weeks. The chemical effects related to the anodic processes were investigated. The observed pH acidic shift was justified by the increasing current demand due to paint damage and brucite precipitation on the panels. The necessity of anode isolating glass to prevent chlorine related chemical attack over the paints, potentially affecting the disbondment result, was verified. In conclusion, current monitoring, pH control and anode isolation are highly suggested to correctly interpret the cathodic disbondment results when CDTs requiring large electronegative potentials are applied for long periods.

Cathodic disbonding tests operating at large cathodic potentials for long periods need current monitoring, pH control and anode isolation

Filippo Castelli;Roberto Stifanese;Marco Faimali;Marina Delucchi
2022-01-01

Abstract

Metallic structures in service in seawater are protected coupling cathodic protection and paints, where the former may induce disbondment of the latter. A preliminary evaluation of the cathodic disbondment risk can be made by cathodic disbondment tests, CDTs. Many CDTs use cathodic potentials as large as E < -1400 mV vs SCE applied up to 90 days. Only two CDT protocols require contemporary anode isolation, current and pH monitoring, without its correction. These three aspects were considered to develop a hybrid CDT; it consisted in polarizing steel panels at -1500 mV vs SCE for 12 weeks. The chemical effects related to the anodic processes were investigated. The observed pH acidic shift was justified by the increasing current demand due to paint damage and brucite precipitation on the panels. The necessity of anode isolating glass to prevent chlorine related chemical attack over the paints, potentially affecting the disbondment result, was verified. In conclusion, current monitoring, pH control and anode isolation are highly suggested to correctly interpret the cathodic disbondment results when CDTs requiring large electronegative potentials are applied for long periods.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11567/1092657
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