A new accelerated corrosion test for marine paint systems used for ship's topsides and superstructures

Several studies sponsored by the French Naval Authorities have been conducted during the last 10 years aiming to develop more reliable testing conditions than the conventional neutral salt spray test that should not be used for prediction of material performance. A satisfying correlation to atmospheric field exposure on a ship in service was observed using a 6 months cyclic test from the automotive industry (e.g., Volvo STD23‐0014) with a deviation inferior to 25% and an acceleration factor of 4. The possibility to shorten the test duration with a target of 3 months without losing correlation to field exposures is investigated in the present study. A design of experiment is used to study key parameters such as NaCl concentration, the mode of salt application and its frequency as well as the temperature. Ten different marine paint systems used for shipbuilding have been selected. The results indicate an enhancement of the aggressiveness of the test when doubling the salt concentration from 1 to 2 wt%, increasing the number of salt spray per week (from 2 to 3), and the temperature from 35 to 45 °C. The data are compared to marine field exposures in tropical and temperate climates. The most reliable testing conditions to field exposure in marine sites of severity from low C5M to CX on steel include cyclic corrosion tests using 2 wt% of NaCl. The optimal testing conditions which would better simulate field exposure in marine atmosphere of corrosiveness class C5M to CX sites included the tests using 2 wt% of NaCl i.e. SC2. These tests presented the lowest coefficient of variation i.e. less than 40%. The acceleration factor varies significantly upon the site.