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This paper describes experimental work investigating the influence of steel surface roughness on the adhesion performance of fusion bonded epoxy (FBE) pipeline coatings. The paper begins with a summary of the standards and methods that can be used to measure surface roughness. Several parameters are used to characterize the roughness of a blast cleaned steel including profile peak height and peak count. Tortuosity and rugosity indicate the proportional increase in steel surface area developed by roughening the surface. Normal pipeline coating industry practice is to specify and control a single roughness parameter termed “surface profile”. It is measured with replica tape and corresponds to the maximum peak-to-valley height.In the experimental work steel panels were abrasive blast cleaned with various steel shot and grit abrasives and the roughness characteristics of the blast cleaned surface were measured with stylus profilometers conventional replica tape and 3D imaging of replica tape.A FBE pipeline coating was applied to the prepared steel panels. The adhesion performance of the FBE coating was evaluated using the following test methods.<ul><li>Hot water immersion adhesion rating per CSA Z245.20 section 12.14 </li><li>Pull-off adhesion strength after hot water soak exposure per ASTM 4541 </li><li>Cathodic disbondment radius at 65 and 80 °C per CSA Z245.20 section 12.8 </li><li>Time before blisters were observed in Atlas Cell per NACE TM0174 modified </li><li>Average blister diameter in Atlas Cell </li><li>Pull-off adhesion strength after Atlas Cell exposure per ASTM 4541 </li></ul>The experimental data were analyzed using statistical techniques to investigate the relationship between the measured surface roughness and the adhesion test results. The adhesion results were found to be positively and linearly correlated with substrate tortuosity and rugosity. Profile peak height and peak count were found to contribute to tortuosity.
In case of Off-shore platforms there are operated for more than 25 years in severely corrosive environment. It is necessary to keep high quality coating performance for long-term operation period without maintenance.The performance of a coating is significantly influenced by its ability to adhere properly to the substrate material and steel preparation is the essential first stage treatment of a substrate before the application of any coating.With regard to steel preparation ISO 8501-3 specifies preparation grade of welds edges and other area with surface imperfection. The interpretation of preparation grade vary with depending on requirement level of client because it is visual assessment standard not quantitative.To study the effect of surface imperfection affecting long-term durability of coating performance on offshore coating system the carbon steel surface was prepared by different preparation grade based on ISO 8501-3 type of imperfection about weld profile weld porosity and thermally cut edge.This study will look at the correlation between surface imperfection and coating performance on the basis of NORSOK M-501 and ISO 20340 test method including ageing resistance and sea water immersion test for 6 months.Keywords: Off-shore platform ISO 8501-3 surface imperfection weld profile weld porosity thermally cut edge NORSOK M-501 ISO 20340 ageing resistance sea water immersion
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Coating performance and longevity is highly dependent on the quality of substrate surface preparation. The effect of profile height, profile type (e.g., type of tool used to perform the prep, angularity of profile, etc.), extent of cleanliness, and amount of chloride contamination on coating performance were all studied to determine the correlation between these factors in an attempt to identify the primary factor in coating failure due to improper surface preparation.
Many coating product data sheets call for surface profiles of 3-4 mils. Others call for 1.5-2 miles surface profile for a very similar coating type – why should this be? To start to understand this we need to first of all look at why we measure the surface profile on steel surfaces. It pretty much comes down to two main things.