Coating system of a cargo container belonging to a high-profile cargo company failed terribly during service at the humid south gulf coastline. The failure occurred during the summer of 2020 after only 8 months of service. The container had an acknowledged life expectancy of 20 years. An investigation commission was appointed to investigate the root causes of the coating failure. Visual inspection revealed checking and cracking all over the container surfaces including surface rust and rust stains at damaged/cracked locations. Holiday testing revealed multiple holidays/voids for the coating examined at various locations of the container. Dry film coating thickness was also carried out and it showed several locations which were undercoated or excessively over coated. Pencil hardness test was carried out on several locations and it should surface roughness/hardness. A section of coating removed from the container surfaces was randomly taken and analyzed using SEM/EDS technique to see the different layers of the coating and to check the constituents at the base of the coating where the base metal layer was also visible. Pull off adhesion testing carried out on the limited sampling showed at least two out of five readings which did not meet the specification limits for adhesion compliance. Tests conducted below the failed coating system showed evidence of high levels of salt. Flexibility test was performed to check the flexibility of the coating. The failure mechanisms were discussed and good engineering practices were put forward to combat and mitigate poor adhesion and inhomogeneous coating application.
Coatings are a composite blend of raw ingredients that are mixed, applied to a prepared substrate, and dried and cured correctly to perform to their maximum capability. Failures and defects can appear themselves at numerous times in the life of a coating. Prior to application, they can take the shape of settlement and skinning, during application as runs and sags, shortly after application as solvent popping and orange peel, and during service as blistering and rust spotting. Therefore, it is not unexpected that those coatings can suffer from premature failure and/or exhibit defects that may or may not result in failure. Coatings nowadays are the most efficient method to shield metals and thus has been widely engaged among various protective techniques1, 2. There are mainly three protective mechanisms involved, namely resistance barrier, inhibitive pigments and adhesion3, however, it is quite inevitable that the deterioration of coatings, arising from processes such as corrosion of substrates, blisters, and cathodic disbondment etc., may occur during its period of service. Once this happens, the adhesion between the coating and the substrate will be decreased, which will subsequently induce the occurrence of peeling. As a result, coatings will no longer provide protection for the underlying metals. Therefore, the study of failure mechanism of organic coatings is of great importance and has so far attracted much attention in the coatings industry.