ABSTRACT

Water-jetting is frequently used as a surface preparation method during the maintenance of offshore assets. However, water-jetted surfaces are also subject to flash rust formation in the time interval between surface preparation and coating application. The formation of flash rust increases with temperature, relative humidity, and soluble salt contamination on the surface. To prevent flash rust to form and develop, flash rust-preventing inhibitors (FRP) can be utilized.

Three commercially available alkaline aqueous FRPs together with three different corrosion protective coating systems were selected for this study.

A wide range of standardized exposure tests was performed to investigate the performance of the different coating systems on various substrates under atmospheric and submerged conditions.

Based on the overall evaluation of the laboratory exposure test results it can be concluded that the three FRPs tested have no significant effect on the performance of the coating systems during exposure testing when compared to grit-blasted substrates. However, samples with water-jetted surfaces with light flash rust (WJ-2L) show in general an improved performance compared to grit blasted and substrates treated with inhibitors. This may be attributed to a slight passivation of the steel surface stemming from the presence of the flash rust. Subsequently, this study shows that the use of inhibitors may be deemed unnecessary if the development of flash rust is limited. Moreover, if necessary to prevent the development of extensive flash rust, the use of FRPs is expected not to have any significant negative effect on the performance of corrosion-protective coating systems.

INTRODUCTION

Water jetting is frequently used as a surface preparation method mainly during maintenance. However, water-jetted surfaces are prone to the formation of flash rust in the time interval between surface preparation and coating application. The formation of flash rust increases with increasing temperature, relative humidity, and salt contamination concentration on the surface. To prevent flash rust to form and develop, flash rust-preventing inhibitors (FRP) can be utilized. However, the coating manufacturer must agree with the use of FRPs in combination with the candidate coating system.

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