Self-healing coating system

Paul Boughton

Damage to a coating is almost unavoidable during transportation, construction and service. Damage to coatings may expose the substrate to possible corrosion. Cathodic protection systems are installed to act as a back-up for coating imperfections for immersion in the case of underground pipelines. However, cathodic protection systems interact with the coating by chemical and physical phenomena, which can lead to cathodic disbondment of the coating. Corrosion may occur underneath the disbonded coating, which is a risk for asset owners. Above ground or at offshore platforms, cathodic protection is not in place as a back-up system.

Testing for cathodic disbondment of all types of regular ‘conventional coatings’ often reveals disbondment to a certain extent. Contrary to this, properly formulated visco-elastic polymer coating systems do not show any disbondment at all, due to the novel self-healing effect of small defects.

Testing for cathodic disbondment is always done on newly applied coatings, which are only tested for a short period of time, eg 30 days. Lifetime expectancy of assets however are much longer, typically 30 years or more. During its operating lifetime a coating will age and lose essential properties such as adhesive strength. This can be simulated by hot water immersion testing followed by peel- or dolly testing. Results obtained with cathodic disbondment testing do not make much sense if over time the coating spontaneously disbonds because of the its ageing processes.

Stopaq visco-elastic coating systems have proved not to be vulnerable to ageing in hot water immersion tests; values obtained with peel testing after hot water immersion at Tmax + 20°C for 100 days were similar to values obtained with non-aged test specimens and the self-healing effect – a typical property of Stopaq coating systems – still completed within the expected period of time.

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