Effects of Application Methodology on Barrier Film Integrity and Performance of Polyurethane Coatings on Steel Water Pipe per AWWA C222

摘要

The use of polyurethane materials as corrosion protection for welded steel pipe has increased in the past decade. Application of the polyurethane materials is primarily by steel pipe fabricators and the fast setting properties of the polyurethane materials lends to their use in production line environments. Some manual or spray application is still required for non-production pieces (specials, outlets, etc.). Post-production quality testing required by AWWA C222 and most specifications has focused on adhesion testing using ASTM D4541 with wide ranging results and levels of satisfaction from fabricators, engineers and owners. The systematic and random error inherent to this type of adhesion testing is documented in the governing standard and in the more recent literature, particularly when applied to curvilinear pipe surfaces and plant (non-laboratory) environments. Corrosion protection by a coating is provided by providing a barrier between the environment and the steel surface. A more monolithic barrier provides better protection. Despite the amount of testing and investigation of polyurethanes by coating manufacturers and others, little attention has been paid to the characteristics of the resulting polymer film. In this work, we investigate the characteristics or "microstructure" of a variety of polyurethane materials; both hand applied and plant applied polyurethane materials were compared and analyzed. The microstructure may include interfacial planes (if the film was applied in multiple passes) and voids or bubbles resulting in porosity. Hand applied material was in general more porous than plant applied with the degree of porosity of plant applied material varying over a wide range. The impact of porosity on corrosion protection effectiveness is discussed.