Rust Staining

Coatings are constantly exposed to different environments during their lifespan. These environments include immersion in substances like ballast tanks or storage tanks, exposure to general atmospheric conditions as outlined in ISO 12944-2 (referred to as the Corrosivity table), or contact with various cargoes in areas like cargo holds or silos.

When coatings break down due to factors like thin film thickness, mechanical damage, or general wear and tear, the steel substrate underneath is exposed to the elements and begins to form rust (ferric oxide). When this happens in the presence of water, adjacent intact coating surfaces can become stained with rust. The extent of staining can vary depending on the specific environment. For instance, ballast tanks, which are frequently filled and emptied with salt water, often experience significant rust staining where steel is exposed.

Rust staining can make it difficult to accurately assess the condition of coatings during surveys, especially in terms of the extent of rust formation on the steel substrate. Coatings can also experience general staining when in contact with different cargoes. This can include coal and coke cargo in bulk carrier holds, crude oil in cargo tanks, or dirty water in ballast tanks. This type of staining may appear as surface discolouration or leave deposits that dry on the coating and are hard to remove.

Inspecting coatings with general staining can pose challenges for coating surveyors. Additionally, externally exposed coatings in atmospheric locations can accumulate general contamination, such as greases, oils, fluids, dust, or debris.

Coating surveyors need to be aware of these factors before conducting surveys to accurately assess the condition of coatings. Coatings Radar App has an interactive 3D coating assessment program for tank linings that have been subject to immersion with comparison to the Re Scale.