Volume 6, Issue 3 (March 2009)
Electrochemical Quartz Crystal Microbalance Technique to Monitor External Polymeric Pipeline Coatings
Electrochemical Quartz Crystal Microbalance (EQCM) can be used to monitor changes in several material properties, including mass, electrochemical, viscosity, adsorption, and deposition. In this paper, EQCM was evaluated to determine if it can monitor changes to the metal-coating interface well before any visible/physical changes to the coating. Modified cathodic disbondment (CD) experiments were carried out over a period of 14 months on 13 coatings used to protect the external surfaces of oil and gas pipelines. During the experiments, EQCM measurements were recorded by placing the quartz crystal at the coating-steel interface. After the experiments, the CD area was measured and compared with the EQCM measurements. Of the 117 panels of 13 different pipeline coatings tested, for 67 % of coatings EQCM correctly predicted the coating performance. Twenty-five percent of coatings performed better than that predicted from EQCM data. Only for 8 % of coatings EQCM measurements predicted better performance but the coatings disbonded during CD area measurement. Based on these observations it was concluded that microscopic changes to the metal-coating interface could be assessed from oscillation frequency of the EQCM crystal placed at the metal-coating interface. However, in order to obtain useful information, extreme care should be exercised in placing the fragile EQCM crystal at the metal-coating interface.