Internal corrosion occurs in natural gas pipelines primarily due to the presence of water, carbon dioxide, and hydrogen sulfide. Internal corrosion can eventually result in leakage, cracks, and rupture of the pipeline. The objective of this work is to mitigate internal corrosion in steel pipelines transporting natural gas using cold spray coatings. The corrosion behavior of carbon steel coated with self-healing ZnCr and ZnNb cold spray coatings was investigated in a natural gas environment. For comparison purposes, hot-dip galvanized steel (HDGS) was tested under the same conditions as cold spray coatings.
The field test was performed at the NW Natural gas storage facility in Mist, Oregon. The field test was conducted in a 6-inch diameter pipe transporting wet natural gas out of an underground storage well at 500 psi and 40o F. The coupons were tested for 15 and 32 days under stagnant and flow conditions, respectively. Weight loss method was used to measure corrosion rate of metallic coatings. Post-corrosion surface characterization was performed on the specimen using a scanning electron microscopy (SEM) equipped with energy dispersive X-ray spectroscopy (EDS). Crystalline phases were determined by X-ray diffraction (XRD). The field-test results confirm that the metallic coatings provide corrosion protection of carbon steel exposed to wet natural gas under stagnant and flow conditions. The formation of the ZnCO3 layer on top of ZnNb and ZnCr coatings led to passivation of the coatings which helps to reduce the self-corrosion. These layers form a barrier for diffusion of corrosive species to the surface.