For the viscous-elastic coating materials, the most prominent claims by the coating manufacturers are impermeable to water, self-healing, low or no undercreep (rust creepage), and no disbondment. These aspects were examined by a comparative evaluation on the performance characteristics of four viscoelastic materials using a specially designed test program. The tests were carried out in 3% NaCl water immersion conditions at 4, 25, and 65ºC for 100 days, coupled with the use of electrochemical impedance spectroscopy (EIS) to periodically monitor the progress of water permeation and interfacial corrosion behavior of the undamaged materials. Water uptake derived from EIS modeling confirmed that all four viscoelastic materials had higher water permeability at higher temperature; however, peel adhesion test revealed lower adhesion on some materials after 100 days immersion at lower test temperatures. With the EIS technique, in-depth data interpretation leads to a proper understanding of the probable mechanism of lower adhesion at lower temperatures. The resistance to undercreep was also investigated on the test materials with an artificial defect used to mimic mechanical damage to coating. The examination results proved negligible undercreep but significant delamination at 65 ºC was observed on all four test materials. Cathodic disbondment testing also confirmed that viscoelastic materials will disbond under cathodic protection, but the extent of disbondment will vary between the different viscoelastic test materials.
Key words: viscous-elastic coating technology, comparative evaluation, water immersion, EIS, modeling, peel adhesion, underfilm corrosion, cathodic delamination, cathodic disbondment