The inhibitory performance of three distinct protic ionic liquids (PILs), namely, 2-hydroxyethyl ammonium formate (PIL 01), 2-hydroxyethyl ammonium propionate (PIL 02), and 2-hydroxyethyl ammonium pentanoate (PIL 03), was evaluated to determine their suitability as eco-friendly corrosion inhibitors for carbon steel (ASTM A36) in a 3.5 wt. % NaCl aerated neutral electrolyte solution. Standard corrosion inhibitor assessment methods, including electrochemical impedance spectroscopy (EIS), potentiodynamic polarization (PDP), weight loss measurements, and microscopic techniques (SEM and optical microscopy), were employed to examine the steel surface and corrosion rate. There is a general agreement that the inhibition efficacy is directly associated with the adsorption capacity of substances on the surface of an investigated material, normally stainless or carbon steel. The standard free energies of adsorption were approximately −22 kJ mol⁻¹, indicating a physical adsorption type of interaction between ionic liquids and the electrode surface. The adsorption behavior of protic ionic liquids on an A36 steel surface conforms to a Langmuir-type isotherm. In conclusion, PIL 01 demonstrated an inhibition efficiency exceeding 80%, while PILs 02 and 03 exhibited efficacies in the 50–60% range. The inhibition efficiency was observed to be proportional to the inhibitor’s concentration. These results suggest that PIL 01, PIL 02, and PIL 03 exhibit significant corrosion inhibition properties.

Currently, surface treatments lead to inducing a superficial layer of several nanometers up to micrometer, which in some cases can be protective. In this experimental work, an oxide layer was generated under different atmospheres (CO₂ and steam atmospheres) during the thermal aging treatment of two different maraging grades, 300 and 350. Afterwards, this layer was microstructural and mechanically characterized by advanced characterization techniques at the micro- and submicron length scale to highlight some information related to the generated oxide layer. The results showed that the oxide layer (in both grades) was made up of several compounds like: TiO₂, MoO₃, hematite (α-Fe₂O₃), and CoFe₂O₄, this being the majority compound distributed homogeneously throughout the layer. Furthermore, a nickel-rich austenitic phase at the interphase was mainly made up cobalt ions (Co²⁺), instead of iron ions (Fe²⁺), within the spinel lattice.

This study conducts a comparative electrochemical evaluation of three types of pearlitic steels used in flexible pipelines for oil transport in marine environments. The steels have been manufactured with chemical composition and geometry variations to optimize operation performance under adverse conditions. Electrochemical tests were conducted using solutions simulating marine environments with NaCl and CO₂, and at high temperatures. The results indicated that spheroidized (SC) steel demonstrated the best corrosion resistance under these specific conditions. Additionally, the Raman spectroscopy characterization technique was used to analyze the layers of corrosion products formed during the tests, identifying the presence of FeCO₃ (siderite) and other corrosive oxides. These discoveries are valuable for selecting and improving materials in flexible pipelines used in oil production in marine waters. The study highlights the importance of the cementite morphology present in pearlite as a relevant factor in the corrosive behavior of steels, contributing to the development of more efficient and durable solutions for the offshore oil and gas industry.