ABSTRACT

Understanding wet adhesion behaviors of protective coatings is a subject of considerable interest, as the durability of the interfacial adhesion between coating and steel substrate is the key element in controlling coating lifetime, especially in buried or submerged conditions. Previously published work has confirmed that there are significant effects of different blast abrasives on the corrosion resistance of liquid-applied epoxy pipeline coatings. This study explores the disbondment response versus test temperature of the same coating on surfaces prepared by various abrasives. The test results are not only beneficial for selecting appropriate abrasives for specific service requirement, but also essential for the development of reliable accelerated ageing protocols to evaluate pipeline coatings. Despite the importance of surface preparation, application also plays key role in a coating's performance and these factors (e.g., mixing ratio, variation of coating film thickness) were examined and discussed. The long-term performance prediction was verified by testing the coatings applied on the surfaces prepared by the best abrasive performers in cathodic disbondment testing and hot water immersion for extended test duration.

INTRODUCTION

Protective coatings provide the primary defense against corrosion of pipelines. Adhesion is one of the most crucial properties for coatings to function properly and support successful long-term integrity. If the bond between the coating and substrate is weak or deteriorates, the coating ceases to be attached to the substrate, and the coating loses its effectiveness and eventually fails1. Surface preparation by dry blasting is commonly facilitated to produce the required surface roughness and cleanliness to maximize adhesion for pipeline coatings. Understanding wet adhesion behaviors of protective coatings is the subject of considerable interest, as the durability of the interfacial adhesion between coating and steel substrate is the key element in controlling coating lifetime, especially in buried or submerged conditions. The previously published work2 prepared fifteen (15) NACE No. 2/SSPC-SP 10 surfaces with the achieved anchor profiles in the range of 3 - 4.5 mils using ten (10) different abrasives. The study revealed that despite the two liquid-applied epoxy pipeline coatings (coating A and coating B) under study achieved superior dry adhesion results on all 15 surfaces, significant performance variations were observed in cathodic disbondment (CD) and hot water immersion (HWI) tests. These surfaces were analyzed for peak height, peak density/count, and tortuosity and no meaningful correlation was observed with these parameters and the resulting performance in the CD and HWI testing. The experimental evidence confirmed that the effects of different blast abrasives on the corrosion resistance of liquid-applied pipeline coatings are enormous. Good coatings would prematurely fail in a short period of time if an incompatible abrasive was used. Accordingly, these abrasives were categorized as worst, mediocre, and best performers by the authors, thus representative abrasives can be selected for further study to scale down the work. Both coatings showed poor performance on glass abrasives prepared surfaces, so the type of abrasives was graded as the "worst performer". The "best performers" were assigned to mineral grit and mineral blend abrasives as both coatings showed good performance on these abrasively prepared surfaces. Coating A on all three steel abrasives and the garnet prepared surfaces also displayed good performance, therefore the types of abrasives were regarded as the "best performer" for coating A. Coal slags were deemed as "mediocre performers" for coating B due to overall acceptable performances were observed.

This content is only available via PDF.
You can access this article if you purchase or spend a download.