Mechanisms of Disbonding of Pipelline Coatings. Annual Report, March 1, 1991-February 28, 1992.

摘要

The objective of this program is to characterize the mechanism of cathodic disbonding (CD) of pipeline coatings from steel pipe to (1) improve surface and coating preparation for resistance to CD, and (2) place currently used practices for evaluating CD resistance on a more rational basis. The approach entails characterizing the chemistry of surfaces undergoing CD and the chemistry of the disbond zone. A method for directly transporting a metal sample from a disbond zone to an ultra high vacuum for surface analysis using Auger electron and photoelectron spectroscopies has been developed in this first year. Results obtained this year show that the environment within the disbond zone produced by a standard CD test has a pH in excess of 13. Electrochemical impedance spectroscopy (EIS) has also been used to characterize the physical properties of the disbond zone and the transport of water through typical fusion bonded epoxy (FBE) coatings. EIS demonstrates that disbonding of FBE from a contaminated substrate can result in shielding. However, well bonded FBE can take up to 20% water as determined from EIS without showing signs of corrosion of the substrate or coating degradation.