There are two well recognized international standards to evaluate offshore atmospheric coatings. One is ISO-12944-9 (historically referenced as ISO 20340) and the other one is NACE TM 0404 (new construction)/TM 0304 (maintenance) with acceptance criteria referenced in NACE SP 0108. The major differences between the ISO and the NACE standards are the cyclic test method and the test duration for the rust creepage test. The ISO requires a 25-week cyclic test duration and NACE standard requires 12 weeks only. Furthermore, the NACE standard requires other coating properties - edge coverage (retention), thermal cycling and coating flexibility to be evaluated.
In this experimental program, ten coatings (zinc rich epoxy and non-zinc rich epoxy) systems are evaluated using both test standards. The coatings were applied on grit blasted new steel panels to SP-10 surface cleanliness. The rust creepage test results reveal both standards can differentiate the same good and bad coating systems. In a comparative coating performance evaluation, the NACE method provides an efficient and holistic approach towards reliable coating system selection for offshore platforms.
ISO 12944 (& ISO 9223) has six different corrosivity categories and assigns offshore environment CX (previously C5-M) the highest corrosion category In such a corrosive offshore environment, combined with imperfect application and risk of damage, the offshore platform coating service life can be short (<8 years) resulting in large scale maintenance programs. The price per square foot of maintenance programs are typically an order of magnitude higher than the new construction/erection costs. The maintenance costs can vary but is high and depends on ease of execution, type of maintenance and other factors influencing execution. Therefore, it is desirable for facility owners to select long service life offshore coatings and optimize the total expenditure related to maintenance.
There are two well recognized international standards to evaluate offshore atmospheric coatings. One is ISO-12944-91 (historically referenced as ISO 203402) and the other one is NACE TM 04043 (new construction)/TM 03044 (maintenance) with acceptance criteria referenced in NACE SP 01085. The differences of these two standards are listed in Table 1.