The aim of this research is to investigate the effect of variable compositional coating layers on their mechanical and chemical behaviour under certain environments typically experienced in the Oil and Gas Industry. The research centers on using thermal spray coating techniques such as the HVOF and plasma spray equipment. The coating was applied onto selected carbon steel substrates (API-5L, Schedule-40, Grade-B) to simulate the material application used in oil and gas components that subject to corrosion and corrosion-erosion phenomena. The coating was deposited using three layers of coatings with various combinations of sprayed powders to create graded multi-layered coating. WC-12Co powders with two different powder structures (micro-sized powders and nano-sized agglomerated into micro-sized powders – nano-structured) were mixed at different ratios with AMDRY (9954 and 995M) powders to enhance the mechanical behaviour, wear, and corrosion protection (Hardness, corrosion, erosion-corrosion) of the coatings. The surface morphology and the elemental composition of the coatings were examined using SEM and EDS techniques. The results indicated that coating deposited by the HVOF (60% Micro WC-12Co and 40% Micro AMDRY 9954) was the most effective coating system in preventing corrosion. If the erosion is the dominant concern, then replacing the Microsized WC-12Co powder with the Nanosized WC-12Co powder is effective for protecting materials from wear caused by erosion-corrosion. The addition of the AMDRY powder to the original WC-Co powders helped to lower the overall coating porosity, enhanced the corrosion protection, and improved the overall erosion–corrosion performance, which addresses issues currently faced in the Oil/Gas industry. A Design of Experiment (DOE) technique may be used to optimize the powders blending ratios to give better results in future work.