Evaluation of Compatibility Between Thermal Insulator, External Coating, and Cathodic Protection at 150 °C

Due to operational requirements including the production of heavy oil from oil-sands by the Steam-Assisted Gravitational Drainage (SAGD) process, the operating temperature of pipelines is increasing.  Pipelines are being operated at temperatures as high as 150^oC.  To maintain such temperatures, the external surface of the pipeline is protected by an insulator in addition to an anti-corrosion coating. All underground pipelines are further protected by cathodic protection (CP).

The cathodic disbondment (CD) test is commonly used for determining compatibility between external polymeric pipeline coatings and CP. This test measures the coating disbondment caused by electrical stress. The test evaluates the ability of the coating not to loosen or disbond under the stress of the imposed cathodic potential. Several standard procedures are available to conduct the CD test at temperatures up to 65^oC.  

This paper describes the evaluation of compatibility between the insulator, anticorrosion coating, and cathodic protection at 150^oC. Experiments were carried out using 1, 1.5, 2, and 2.75 inch thick insulator coatings.  During the 30-day experiment, the CP current demand was monitored online and the electrical conductivity of the environment surrounding the pipe sample was recorded daily.  Electrochemical impedance spectroscopy (EIS) was also performed daily to evaluate its ability to monitor deterioration of coating.  The influence of holiday depth and insulator thickness on the area of cathodic disbondment and CP current demand was investigated.