The demands on protective coatings used in offshore environments are very high and modern high performance paint systems are so durable that when exposed to natural weathering they may show only slight signs of deterioration. The best anticorrosive coating systems of today may continue to perform well for maybe 15-20 years. The use of new technologies also means that coatings being marketed have limited track record. This has resulted in a necessary increase in reliance on accelerated laboratory testing to evaluate coating performance. However, many of these accelerated exposure tests will not, within their exposure time, show negative effects on intact coating systems. Therefore rust creep from artificially made damage is receiving significant consideration. Rust creep, according to the existing standards, is evaluated by a ruler after removal of the paint around the score. This evaluation method is destructive which means that one panel only gives one reading of rust creep and in addition the method is rather time consuming. This paper presents a new non-destructive test (NDT) method which makes it possible to record the progress of rust creep during the exposure time without removing the paint. The advantages of using this method are that the same panels can be investigated several times during the exposure time; the method is fast and exact and it provides early prediction of the final rust creep.
The protective coatings used in marine environments are exposed to combined actions of salt spray, rain, snow, frost and sun in random order. The condition will vary from location to location and even with season. The demands on protective coatings used in these harsh offshore environments are very high but modern high performance paint systems are so durable that exposure to natural weathering may show only small signs of deterioration. If an anticorrosive coating is intact during its service life or during testing it may, for the best present products of today, maintain a high performance for 15-20 years. The use of new technologies and paint formulations also means coatings being developed with limited or no previous track record. This has resulted in more emphasis being placed on accelerated laboratory testing to evaluate coating performance. The accelerated weathering methods seek to intensify the effects from the environment so that the breakdown of the coating system occurs more rapidly. However, imitating real life conditions in accelerated testing is not an easy task and many of these accelerated exposure tests will not, within the defined exposure time, show the negative effects on intact coating systems. Many parameters determine the lifetime of a coating system and the governing accelerated test methods have been developed over many years1&2. The correlation between real life performance and accelerated testing in the laboratory is generally a requirement in the evaluation of any material and in the protective coatings area a lot of effort has been undertaken to develop and improve such methods. Accelerated test methods based on cyclic exposure and behavior around artificially made damages such as scores are given significant consideration and seem to give better ranking of anticorrosive coating systems than standard constant exposure tests.
