Laboratory and Field Investigations of the Performance of HPCC Coatings Available to Purchase

Three-layer FBE-polyolefin coatings offer the promise of good adhesive and corrosion properties from the FBE layer coupled with resistance to mechanical damage from the outer polyolefin layer. TransCanada Pipelines have been investigating the long-term behaviour of High Performance Composite Coating (HPCC) using a combination of laboratory testing and field trials. In the laboratory, panels of HPCC were subjected to standard CD disbondment testing following a two-stage degradation process. The degradation process, designed to simulate field exposure, involved impact damage followed by exposure to either a hot-water soak (60°C), or to microbiologically active soil with and without the application of CP. Following exposure, the duplicate panels were subject to 28-day CD disbondment tests to determine the extent of damage caused by the combination of impact and soil/hot water exposure. In the field, a section of HPCC coating was excavated and examined after 11 years service. In addition to visual inspection, the coating was examined in situ using a newly developed impedance technique EISPlus. This technique is a development of earlier EIS techniques and allows the dielectric properties of the coating to be determined in addition to the impedance of the solution-filled pores. EISPlus provides an improved sensitivity for high-impedance coatings, such as FBE, HPCC, and polyolefin tape. Furthermore, since it is a dry technique, rapid measurements can be made on coatings exposed to field conditions allowing the in-service performance to be determined. Results of both the laboratory testing and field EISPlus measurements are presented and the long-term performance of the coating discussed.