| Cathodic disbonding is one undesirable aspect of the combination of the corrosion control technology commonly used for the exterior of buried pipelines. This technology consists of the combined use of protective coatings and cathodic protection. While standard cathodic disbonding tests performed in the laboratory provide a relative ranking of coatings, due to the simplicity of the test environments and accelerated nature of the tests, the results may not necessarily be directly related to service performance. Therefore, the objective of this work was to determine the cathodic disbonding behavior of three commonly used pipeline coating materials (i.e., fusion bonded epoxy, coal tar enamel, and tape coatings) under more realistic conditions.; The research plan allowed the comparison of cathodic disbonding tests results between standard and realistic conditions by utilizing laboratory tests with controlled environments and cathodic protection levels. Several areas of focus were the effects of a moderate level of polarization, high level of polarization, and elevated temperatures. Additional factors examined included electrolyte composition (soil extract versus NaCl solutions), wet/dry cycling, and simulated soil conditions (i.e., sand moistened with soil extract). These tests delineated the effects of test parameters on cathodic disbonding and coating performance was related to these parameters. The processes considered to be important to the cathodic disbonding behavior of coatings are discussed as well as the implications of the realistic test results on laboratory cathodic disbonding test procedures.; It was confirmed that greater disbonding occurred at more negative (i.e., cathodic) potentials, with higher alkalinity, and at elevated temperatures. This study also showed that disbonding increased greatly when sand moistened with soil extract solution was utilized in place of bulk electrolyte. The addition of such a barrier to convection may present a viable method to accelerate cathodic disbonding tests and is more representative of conditions in soils along pipelines. Wet/dry cycling showed no measurable effect on the extent of disbonding. Temperature, however, was determined to be a significant factor. The effect of initial electrolyte composition was not certain when comparing between NaCl and different soil extract solutions. Tests under realistic conditions generally exhibited larger scatter than standard tests, probably due to the added complexity caused by calcareous deposit formations and concurrent alteration of the electrolyte with the use of soil extract solutions. |
