Adhesion and adhesion degradation of a pressure sensitive tape on carbon steel

Corrosion protection of carbon steels by organic coatings is dependent on a good adhesion between coating and substrate. In this work the blister test method was used to study the adhesion of a pressure sensitive tape applied on carbon steel. Deionized water was used to pressurize a blister formed by the tape covering a through-hole in the steel substrate. Values of adhesion strength as measured by the strain energy release rate were determined for two different blister pressurization rates or water injection rates. The adhesion strength was higher for the larger injection rate, which is expected for pressure sensitive tape. These values were probably overestimates of the true adhesion strength owing to plastic yielding of the membrane. Resistance to adhesion degradation near coating defects or macroscopic scribes was characterized using a height regulating scanning Kelvin probe on samples exposed to sodium chloride solution or a salt spray environment. Although the tape exhibited good barrier properties to water and ions, cathodic delamination was observed near the scribe after salt spray exposure. Wet/dry cycles were more aggressive than continuous salt spray exposure, since during continuous exposure corrosion products are washed away. It was observed that the oxide layer grows to a larger extent during wet/dry cycles; therefore, acceleration of the delamination process is probably associated with a “wedge effect” of the oxide on the interface.