HIGH TEMPERATURE CATHODIC DISBONDMENT TESTS

Current test standards for Cathodic Disbondment (CD) tests do not include tests that are close to or above 100 °C; primarily because of difficulties associated with evaporation of the electrolyte in such tests and because there has been little demand for such high temperatures.  However, with the increasing use of pipelines and other vessels at temperatures above 100°C, the need for preferably standardized tests that will evaluate coatings at these higher temperatures has become something that needs urgent attention.   Many currently used CD test standards employ methods that have both pipe sample and testing electrolyte at the same temperature but these tests have not been viable for test temperatures above 80-90°C because of electrolyte evaporation.  This paper describes the development and testing of a high temperature test apparatus that allows for CD testing in a pressurized test vessel.  The vessel allows testing at high temperatures of electrolyte as well as standard potential measurements and control.  It also provides methods for controlling oxygen concentration in the electrolyte.  Comparative data from tests using the new apparatus and other test methods are included that demonstrate the influence of changes in temperature, pressure, and oxygen content in the test electrolyte. Further to this work, another CD test cell was designed, built and tested which incorporates a cooling jacket on the cell such that high temperature CD tests can be run at ambient pressure conditions.  This paper includes discussion of the affects of oxygen concentration levels, electrolyte temperatures, and the merits of the different CD test methods.
Keywords: CD test, high temperature, laboratory test, oxygen levels, CD electrolyte, protective coating, pipeline coating, high pressure, cathodic disbondment, test methods