External pitting corrosion is a serious concern for offshore stainless steel vessels, tanks and piping. Protective coating is an economic option to mitigate the pitting corrosion of offshore stainless steels. However, in the literature, there is a lack of publications on the selection of proper coating systems on pitted stainless steels to minimize pitting growth and prevent new pitting formation.
The objective of this study was to 1) develop a test protocol to test coating performance on pitted stainless steel 2) compare the performance of protective coating systems on various surface preparations, 3) determine a proper coating application procedure to cover the pits, to improve the integrity of offshore pitted stainless steels.
The following lab tests were performed to determine the performance of various coating systems: 1) adhesion test, 2) water vapor permeation, 3) underfilm corrosion, and 4) holiday-free film formation. As a result of this work, protective coating systems and the application method for the pitted offshore stainless steel facilities were identified. The most critical issues for the selection of coating systems for offshore pitted stainless steels are to have a good adhesion durability and low water permeation. The primer must be applied with brush to fill the pits and the rest of coats can be applied by spray.
Key words: coating, stainless steel, pitting corrosion, permeability, adhesion, underfilm corrosion