Binary Sacrificial Coatings for Internal Corrosion Protection of Natural Gas Transmission Pipelines

One of the top reasons for the leaks in natural gas transmission pipelines is related to the internal corrosion of steel pipelines, mainly due to the presence of incidental H 2 O and CO 2 in the line. Adding a protective coating or liner to the inner pipe surface reduces internal corrosion; however, conventional coatings (e.g., paint, epoxy, polyethylene, etc.) are insufficient to provide long-term corrosion resistance due to the permeation of the corrosive species such as H 2 O, CO 2 , Cl - . This research aimed to investigate the corrosion behavior of binary sacrificial coating for the protection of pipeline steel in a CO 2 -saturated aqueous electrolyte under natural gas pipeline conditions. Two types of the cold spray binary metallic coatings (ZnCr, ZnNb) were studied using electrochemical techniques: potentiodynamic polarization (PDP), linear polarization resistance (LPR) and electrochemical impedance spectroscopy (EIS). The evaluation of the corrosion resistance of cold spray binary metallic coatings (ZnCr, ZnNb) was carried out in an environment containing 3 barg CO 2 pressure, simulating the partial pressures that are found in gas transmission over a solution of 3.5 wt.% NaCl heated to 40 ºC. Post-corrosion surface characterization was performed using scanning electron microscopy (SEM) equipped with energy-dispersive X-ray spectroscopy (EDS). The EDS mapping analysis and XRD results revealed the presence of ZnCO 3 layer. EDS analysis showed that no Cr was detected on the surface of ZnCr coating after 24 hours of exposure. This may be due to a thick layer of ZnCO 3 formed on top of the ZnCr coating. The obtained data showed that cold spray binary metallic coatings (ZnCr, ZnNb) can be used as sacrificial anodic materials to protect the interior of the steel pipeline against CO 2 corrosion in a natural gas transmission environment. Furthermore, self-healing properties of the binary metallic coatings were demonstrated as protective corrosion products formed on the damaged regions of the coating. Keywords : CO 2 corrosion, natural gas pipelines, cold spray coatings, zinc alloy, sacrificial coatings, self-healing coatings, electrochemical reaction autoclave