CUI (corrosion under insulation) is a pervasive, difficult and high-liability issue for petrochemical, power, shipping, and other industries. Situational variations (meteorological, geographical, seasonal, etc.) can confound conventionally specified surface preparation attempts to achieve perfect or near-perfect metal hygiene, thus reducing expected coating life by 30 to 75 percent. Because conventional surface preparation processes have historically been unable to adequately relieve microcontamination of metal surfaces, organizations have settled for an uneasy balance between economic and physical feasibilities that exclude the possibility of achieving ideal surface preparation outcomes and rely more heavily upon barrier coatings to supply needed corrosion control.
Zinc-rich coatings have long been known to provide excellent corrosion resistance in highly corrosive environments, in general,inorganic zincs for new construction and organic zincs for maintenance. A recent trend has been toward zinc-rich coatings with reduced levels of zinc dust. An SSPC committee formed to revise SSPC Paint 29, Zinc Dust Sacrificial Primer, Performance Based, to reference performance only, removing reference to minimum zinc dust level.
A continuing problem with coatings applied to sharp edges of a structure is the corrosion that
often develops at the apex of the edge. The conventional wisdom is that the reduction of film
thickness, due to coating pulling away at the edge during the curing of the coating, is the primary
cause for the onset of corrosion. This theory, however, is not necessarily correct, both from a
mechanistic and practical point of view.