Surface coatings are a cost-effective method for protecting metals surface and is well known for versatility, ease of maintenance, and various compositions specific to service involved. In this case study, a detailed investigation was conducted to discover the reason behind the failure of the external coating system (aliphatic polyurethane) on a riveted fire water tank for a turnkey project located in the Arabian Gulf region. Visual inspections of longitudinal seams alongside the failed coatings revealed rust stains which came from the seepage of the service. The under fill / primer layer’s dry film thickness showed significant and consistent variation from the topcoat’s thickness. Pull off adhesion tests advocated an adhesion failure between epoxy primer and aliphatic polyurethane. Cathodic disbondment test confirmed the paint manufacturer’s report and created confidence on the product chemistry. The corrosion mechanism leading to the in service failure of the applied coating is explained.

Subject
Test methods, Primers, Seams, Coating inspection, Water, Coatings, Materials, Manufacturing, Coating damage, Mechanical failure, Dry film thickness, Storage tanks, Coating defects
Keywords:
Coating defects, coating failure analysis, tank coatings
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2022
Association for Materials Protection and Performance (AMPP)
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