L51961 Coating Compatibility at Thermite Welds and Keyhole Excavations

Patching and repairing high performance pipeline coatings requires a high performance repair material to ensure the integrity of the coating system. The application conditions are not optimized as they are during plant applications, so it is imperative that repair coatings applied to mainline coatings will adhere to all coated surfaces so that resources can be focused on optimizing application methods. Compatibility of repair coatings applied to thermite weld components may be inadequate for optimum field performance. When combined with the limiting factors of keyhole excavations it is important to use coatings which are not only compatible with the thermite welds but also are suitable for the keyhole application procedure. A series of 14 pipeline repair coatings were evaluated for their compatibility with the components of a thermite weld. Chemical compatibility was determined in terms of adhesion with the thermite weld individual components: polyethylene wire insulation, polyvinylchloride wire insulation, copper wire, steel, and copper/aluminum thermite alloy. The same coatings were evaluated for their suitability for application by keyhole excavation procedures. A keyhole excavation was simulated using a scaffold over filled soil boxes (dry soil) containing buried pipe sections, and each of the repair coatings was applied by a commercial keyhole excavation company. The ease of application and general suitability was rated. After backfilling and aging for six months, the samples were removed from the soil boxes and the coatings evaluated.