Internal corrosion and sulfide stress cracking (SSC) are problems for steel pipelines transporting natural gas or CO2 containing partial pressures of H2S higher than 0.3 kPa (0.05 psi). The objective of this work is to mitigate internal corrosion and SSC in steel pipelines transporting natural gas containing H2S using cold spray coatings. Two types of the cold spray binary metallic coatings (zinc chromium (ZnCr), zinc niobium (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 coatings (ZnCr, ZnNb) was carried out in an environment containing 4 bar CO2 pressure, simulating the partial pressures that are found in gas transmission lines over a solution of 3.5 wt.% NaCl heated to 40 °C. To simulate sour conditions, a concentration of 0.003 M Na2S2O3.5H2O, which corresponds to H2S partial pressures around 0.079 bar (1.146 psi), was used. Post-corrosion surface characterization was performed using a scanning electron microscope (SEM) equipped with energy-dispersive X-ray spectroscope (EDS) and X-ray diffraction analysis (XRD). The data showed that the presence of 0.003 M Na2S2O3.5H2O shifted the corrosion potential to more anodic values and decreased the corrosion current density. Bothcoatings showed similar behavior after 1 hour of exposure in CO2/H2S environment, which indicated that similar electrochemical reactions were taking place on ZnNb and ZnCr. SEM images and EDS surface analyses for specimens showed a significant change in surface chemical composition of carbon steel coated with ZnNb and ZnCr, after 24 hours of immersion. No localized attack was observed. The EDS analysis and XRD results revealed the presence of zinc sulfide (ZnS).

Natural gas pipelines are subject to internal corrosion. Internal corrosion of steel pipelines can cause natural gas leakage, leading to wasted energy, explosion hazards, and methane emissions. The U.S. Department of Transport reported numerous case histories of corrosion problems and failures in wet gas pipelines. The National Energy Technology Laboratory (NETL) performed an incident survey from 2010 through 2018 and found that 112 (12%) of these incidents in the U.S. transmission lines were caused by internal corrosion.