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Offshore assets such as drilling rigs, production platforms, and wind turbines present challenges for corrosion prevention maintenance. The primary defense against atmospheric corrosion on structural steel in offshore saltwater environments is a protective coating system.
Several factors cause protective coatings to degrade rapidly: besides wearing and damage encountered in installation and use, ultraviolet light breaks down the organic resins and corrosive seawater causes under creep at any breaks in the coating. Maintenance coating for offshore atmospheric systems can therefore be necessary as early as the second year.
A team assembled by a major oil company designed a test program to assess the difference in coating performance between dry abrasive blasting and Waterjetting as surface preparation methods. They were also interested in determining whether using flash rust preventing, decontamination chemical in conjunction with various applications had any effect on coating performance. A glass flake epoxy was used. Panels were treated with 262 MPa (38,000 PSI) Waterjetting, Dry Garnet Blast + Power wash, in both cases with and without a decontamination chemical. Another set of panels was sprayed with ASTM D11413 seawater salt spray after treatment and then coated.
The 300 mm X 600 mm coated panels were saw cut into smaller panels. Some were subjected to per ISO 203401 Ageing Procedure Annex A and ISO 2812-25 Seawater Immersion. Others were submitted to ASTM G 504 long-term field exposure test over 5 years. In both cases, when the decontamination chemical was used, no significant difference in coating performance was detected, including in panels exposed to light seawater mist spray before coating application. The scribed waterjetted panels exhibited more undercreep than abrasive blasted panels, but this undercreep only began to develop after two years.
Proper surface preparation to create sufficient adhesion of a coating over the substrate is fundamentally important in the long-life performance of a protective coating. Abrasive blast cleaning provides a fast and well-established method of surface preparation, which utilizes energy generated by an air supply to deliver a mass of abrasive particles at certain speeds and volumes to impact the steel resulting in a cleaned surface. The method not only cleans the surface to remove rust, scale, paint, and similar contaminations, but also roughens the surface to produce mechanical and chemical adhesion for a coating. Therefore, abrasive blasting is the preferred method for preparing steel for the application of high-performance coatings and routinely used for achieving the required surface conditions prior to a coating work.
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This paper presents an in-sight to the standard “ISO 12944 – Corrosion Protection of Steel Structures by Protective Paint Systems”, from the angle of prevention of premature coating-failure, but also how the standard can be used to help analyze premature coating-failures (if and when a coating-project was done as per ISO 12944).
Inorganic zinc-rich coatings (IOZ’s) are often considered the gold standard for corrosion protection in atmospheric environments. Frequently, zinc epoxy coatings are considered second best among the most effective coatings for corrosion protection. However, current zinc-rich coating technology is not exempt of limitations, such as poor mechanical properties of the film, rigid environmental application conditions, or the inefficient use of zinc particles for providing galvanic protection. Due to these limitations, a number of asset owners have made the decision not to use zinc-rich coatings to maintain coating systems in marine and offshore environments