Evaluation of NETL’s Self-Healing Metallic Coating for Internal Corrosion Protection of Natural Gas Pipelines: Field Test

Abstract Steel pipelines are a safe, reliable, and affordable way to transport natural gas. However, the presence of impurities (e.g., water, carbon dioxide, and hydrogen sulfide) in the natural gas can cause internal corrosion, which can lead to pipeline leaks and failure. This paper reports on field tests of an innovative self-healing, corrosion-resistant, metallic coating developed at the National Energy Technology Laboratory (NETL) for protecting the interior surfaces of pipelines. Cold spray was used to apply the NETL-developed coating to an X52 carbon steel pipe (3 feet long and 6 inches in diameter) for field tests. A 1.5-foot pipe section was coated with ZnCr, and the other 1.5 feet with ZnNb. The field testing was conducted at the NW Natural storage facility in Oregon. The pipe section was pressurized up to 604 psi with untreated natural gas from an underground storage well during the withdrawal season. The pipe section was tested for 131 days under stagnant conditions. After the field test, the pipe section was visually inspected using a borescope. Surface characterization was performed on the specimen from the pipe section using scanning electron microscopy (SEM) equipped with energy-dispersive X-ray spectroscopy (EDS). Crystalline phases were determined by X-ray diffraction (XRD). The corrosion rates were determined by measuring the thickness loss during the field test. The field test results confirm that the metallic coatings provide corrosion protection for carbon steel exposed to wet natural gas under stagnant conditions. Inspection with the borescope detected no visible signs of damage or corrosion to the coating. Surface characterization revealed the formation of a ZnCO3 layer on top of the ZnNb and ZnCr coatings. The ZnCO3 layer provides a barrier that prevents the diffusion of corrosive species to the surface, thereby reducing the corrosion of the coating and extending its service life.