A field study was carried out to investigate if the use of tarpaulin (Tarp) to cover FBE System 1A coated pipelines can protect the coating from ultraviolet (UV) degradation. Actual outside weathering exposure tests for 24-months were conducted on FBE System 1A coated samples with and without Tarp covering. Changes in the coating Flexibility, Photo-oxidative Index (POI) and Carbonyl Index (CI) were examined at different time intervals during the exposure period. The pipeline coating with a Tarp protector showed no reduction in flexibility and only small changes in POI and CI, which indicated that the Tarp successfully protected the pipeline coating from physical and chemical degradation. The pipeline coating without a Tarp protector showed a noticeable decrease in flexibility and increase in POI and CI of the FBE System 1A coating after continued outdoor exposure. Comparison of these results to previously published work on FBE coated samples that were "protected" by UV light blocking topcoats showed that even though the topcoats were successful in stopping UV induced photo-oxidation, the flexibility of the coating system decreased over time. The previous results indicate that the reduction in flexibility of the FBE coating system may be due to factors other than the photo-oxidative damage of the topmost portion of the coating system. Limited DSC studies showed evidence of molecular coordination (long term relaxation) leading to new, less flexible physical structures of the unprotected samples. The DSC results suggest that the flexibility reduction may be attributed to the cumulative effects of photo-oxidation and physical ageing.
Fusion bonded epoxy (FBE) coated pipelines are extensively used throughout the world for transportation of various types of fluids and gases1. New and unused FBE coated pipes often end up being stockpiled in open yards for various reasons such as delay in start of a project, excess inventory etc. Outdoor exposure for long durations results in the physical and chemical degradation of the coating. This happens due to the interaction of the oxygen and moisture in the air, and the ultraviolet (UV) radiation from the sun which causes photo-oxidative degradation of the polymer in the coating. It has been established that UV radiation and oxygen reacts with the carbonyl groups in the polymer resulting in the formation of free radicals and new carbonyl groups.2 Therefore, the rate of carbonyl growth can be a relative measure of the photo-oxidation rate for a given FBE coating system.3 Once photo-oxidation begins, a rapid breakdown of the coating can occur with substantial changes in the physical, mechanical and corrosion protection properties, ultimately leading to failure of the coating. Degradation of the coating manifests itself as ‘chalking’ and depends on the intensity and duration of exposure of the UV radiation. The chalked layer can be removed by wind and rain, exposing unaffected coating and lead to further chalking. The alternate chalking results in a decrease in the coating thickness.