ABSTRACT
This paper describes an experimental study of the influence of steel surface roughness on the performance of a fusion bonded epoxy (FBE) pipeline coating. Steel panels were abrasive blast cleaned with various steel shot and grit abrasives. The roughness characteristics of the blast cleaned surfaces were measured with a stylus profilometer, replica tape per NACE SP0287, and a digital replica tape reader. The 3D topographical data files generated by the digital tape reader were interpreted using surface analysis software. A FBE pipeline coating was applied to the prepared steel panels and the performance of the coating was evaluated using pull-off adhesion strength, cathodic disbondment and Atlas cell wet thermal gradient tests. The strength of correlations among the roughness parameters and the FBE coating performance results were compared. Tortuosity, measured with a stylus profilometer, and developed interfacial area (Sdr), measured with the digital replica tape reader, were found to be strongly correlated with FBE coating performance. The findings of this study suggest that the increase in real surface area developed by roughening the surface is a fundamental roughness characteristic that strongly influences coating adhesion performance.
INTRODUCTION
This paper describes an experimental study of the influence of steel surface roughness on the adhesion performance of a fusion bonded epoxy (FBE) pipeline coating. The aim of the study was to determine which roughness parameters had the most influence on adhesion and what methods would be practical to measure these parameters in a pipe coating plant.
Fusion bonded epoxy (FBE) coatings are widely used to protect oil and gas pipelines against corrosion, as single and dual layer coatings and as the primer in three-layer polyolefin systems. As illustrated in figure 1, FBE coatings may disbond, i.e., lose adhesion, while a pipeline is in service. The corrosion that could occur as a result of disbonded FBE is a pipeline integrity threat, particularly for three-layer polyolefin coatings since corrosion deep beneath a polyolefin layer cannot be mitigated by cathodic protection1.
