Optimization of Fusion Bond Epoxy- Abrasion Resistant Overcoat Thicknesses for Trenchless Installations

Abstract Trenchless installation such as horizontal directional drilling (HDD), direct steerable pipe thrusting, horizontal auger bore, and micro tunnelling have changed how gas and liquid pipeline utilities are installed worldwide. The current HDD technology has moved the limitation of length close to 5 km by creating an intersect method where two rigs drill from two sides towards each other. In 2022, a 4.7 km, 24-inch HDD crossing under Lake Sakakawea (North Dakota) was successfully designed and constructed. As the length increases, there is always a high risk of coating damage when pulling through rocks and gravel. The HDD trenchless construction technique uses a pilot hole (steerable system) along a predetermined alignment and profile to cross under road, rail, and watercourse crossings. When the pilot hole is enlarged by reaming operation, the pipeline is pulled through the bore profile. The subsurface investigation plays a vital role in HDD crossings. The project team should be aware of soil conditions to minimize potential damage to pipe coating during the installation. In North American, fusion bond epoxy (FBE) with an abrasion resistant overcoat (ARO) is the primary pipeline coating system selected for horizontal directional drilling. Industry best practices specify the application methodology for these coating systems along with a minimum anti-corrosion barrier (FBE), but often neglect to specify a minimum, nominal, or maximum ARO thickness (i.e., the sacrificial overcoat). Within this paper, the thickness requirements for FBE-ARO from various pipeline operators will be compared to establish an industry best range. This range of FBE-ARO thicknesses will be compared to the recommended thicknesses from the coating manufacturers. More importantly, a minimum, nominal, and maximum FBE and ARO thickness will be recommended based on laboratory testing from several qualification production tests, field observations, and the manufacturer’s recommendations. The laboratory testing included chemical (e.g., cathodic disbondment) and physical (e.g., impact, gouge) testing that was completed on mill coated pipe. Correlation to field data will also be presented based on various parameters collected from numerous pipeline horizontal directional drilling projects. The data provided will allow for a more informed decision-making process when specifying protective coating for future trenchless installations.