Interfacial Adhesion of FBE Pipeline Coatings by the Notched Coating Adhesion Test

Interfacial adhesion is the most important property of a protective coating for preventing steel substrate from corrosion.  Fusion bonded epoxy (FBE) has been used for quite some time now either as a single layer coating or as a primer for three layer polyolefin coatings.  However, the coating industry has not been able to reliabily measure the interfacial adhesion of FBE coating to steel.  FBE coating has extremely high initial adhesion (estimated to be higher than 6000 psi) that exceeds the conventional pull-off adhesion testing capability.  Its wet adhesion strength has not been successfully measured either.  A glue failure is commonly obtained due to poor bonding to the damp coating surface.  Several different types of knife test are often utilized in several international standards to assess qualitatively the adhesion value.  However, the knife test can detect only poor adhesion (<300 psi).  In order to assess the interfacial adhesion of FBE coating, a reliable and quantitative test method is needed.  In this paper, we report a new notched coating adhesion test method which can be used for measuring the interfacial adhesion degradation of coating, from extremely high initial value to low value due to aging in high temperature in air and/or water immersion.