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).

Sulphide scales, namely iron sulphide (FeS), zinc sulphide (ZnS) and lead sulphide (PbS), are increasingly being encountered in gas/oil wells. These scales can present serious safety concerns, impair well productivity and limit access to downhole tools. There are many published research studies addressing sulphide scale removal and inhibition. However, there is an incomplete understanding of the governing processes of sulphide scale formation and prevention. Furthermore, there are contradictory results in the literature on issues such as the removal procedures and inhibition tests for sulphide scales. Therefore, the main objective of this paper is to critically review the published work on sulphide scale formation, removal and inhibition, to address the factors that control them and to discuss some of the apparent discrepancies in published experimental studies.
The review discusses the formation mechanisms of different sulphide scales in relation to the sources and levels of Fe, Zn, Pb and the sulphide species. The experimental procedures used by different researchers to evaluate sulphide scale dissolvers and inhibitors are described, along with the performance results for the chemistries tested to remove or prevent sulphide scales.
Hydrochloric acid has been shown to outperform rival chemistries for dissolving sulphide scales, however the associated high corrosion rate and H2S generation has necessitated the development of other dissolvers to overcome such drawbacks. Several dissolvers based on chelating agent chemistries combined with catalysts provided high dissolution rates, and the dissolution results and the reaction mechanisms will be discussed in some detail.

Multiple factors have been shown to play a significant role in the inhibition efficiency of sulphide scale inhibitors including pH, salinity, temperature, scale formation sequence and mechanism, and the initial concentrations of sulphide species and scaling metals. In addition, there is a developing understanding of the significance of scale inhibitor consumption in these systems.
Understanding the formation mechanism is essential for accurate interpretation of scale-related issues in the field and for providing the correct treatment strategy. A more complete knowledge of these issues will lead to the further development of reliable procedures for generating dissolution and inhibition results and consequently improving the scale dissolver and inhibitor chemistries themselves.

Metal sulfide mineral scaling, fouling and deposition are frequently encountered problems in geothermal systems. Their formation, crystallization and deposition occur principally because of their extremely low solubility, based on the low solubility product (Ksp). Among the metal sulfides that cause problematic issues, the most common ones are iron sulfide (FeS), zinc sulfide (ZnS), lead sulfide (PbS), and, less frequently, antimony sulfide(s) (Sb2S3 and Sb2S5). Zinc sulfide, for example, has a Ksp of 2·10-25 mol²/L², whereas for PbS, it is 1·10-28 mol²/L² (~ three orders of magnitude less soluble). ZnS can precipitate either as Sphalerite or Zinc Blende, and PbS commonly crystallizes as Galena. Mitigation of such ZnS and PbS precipitates and deposits can be achieved by chemical interventions, by the addition of organic chemical additives to the water. Herein, we report the inhibitory effects of phosphonate-based chemical additives for ZnS and PbS scales. These additives can inhibit formation of sulfide scale, and, significantly, prevent its deposition on metal surfaces. The efficiency of these additives is dosage-dependent, and relatively high inhibitor concentrations are needed for their inhibitory activity to take place. Possible mechanisms will be discussed focusing on inhibition and dispersion.    

Oilfield waters have a complex composition depending on reservoir rock at different geographical locations that can be carried into the production water¹. The alteration in environmental conditions such as pressure, temperature, salt content or pH can cause the liquid to oversaturate and the contained ions to form complexes. These will precipitate out of the solution, deposit and grow on contacting surfaces such as reservoirs, upstream production tubing, sub-surface safety valves, water injection lines to top side refining equipment namely heat exchangers and transport lines ^2–4. Scaling can also be induced by incompatible mixing of fluids. For example CaCO₃ and /or BaSO₄  form through typical mixing of SO4 2- containing sea water with the formation water that carries high concentrations of divalent cations such as Ca²⁺and Ba^2+₂. Similarly, sulfide scales form upon mixing with H₂S-containing  formation water enriched with Fe, Zn or Pb ions ⁵. ZnS and PbS have been observed to form in presence of only 25 ppm H₂S at gulf of Mexico containing 50 ppm Zn and 5 ppm Pb , due to their low solubility constant K_sp ^6,7.  

The increasing need for fossil fuels has resulted in more aggressive drilling and exploitation in oil and gas production industry. As new explorations at more extreme conditions (i.e. high temperature and high pressure) become more frequent, new challenges arise in terms of drilling equipment, operation conditions and safe production. Among those challenges, the mineral scale deposition, as one of the serious problems both for the surface and subsurface oilfields, can cause pipelines plugging, equipment failure and decrease in production efficiency, even emergency shutdown.