Microalloyed steels have evolved in terms of their chemical composition, processing, and metallurgical characteristics since the beginning of the 20th century in the function of fabrication costs and mechanical properties required to obtain high-performance materials needed to accommodate for the growing demands of gas and hydrocarbons transport. As a result of this, microalloyed steels present a good combination of high strength and ductility obtained through the addition of microalloying elements, thermomechanical processing, and controlled cooling, processes capable of producing complex microstructures that improve the mechanical properties of steels. These controlled microstructures can be severely affected and result in catastrophic failures, due to the atomic hydrogen diffusion that occurs during the corrosion process of pipeline steel. Recently, a martensite–bainite microstructure with acicular ferrite has been chosen as a viable candidate to be used in environments with the presence of hydrogen. The aim of this review is to summarize the main changes of chemical composition, processing techniques, and the evolution of the mechanical properties throughout recent history on the use of microalloying in high strength low alloy steels, as well as the effects of hydrogen in newly created pipelines, examining the causes behind the mechanisms of hydrogen embrittlement in these steels.

In this research work, a preliminary potentiodynamic polarization performance testing was carried out on a new environmentally friendly proposed composite coating. The proposed composite coating was developed by: (a) hot sulfuric anodizing to produce an Al₂O₃ conversion film followed by an (b) organic electrodeposited chitosan–sodium alginate blended film. Posteriorly, the conversion and organic films were microstructurally characterized by scanning electron microscopy. Finally, the polarization resistance technique was used to measure the corrosion resistance of the uncoated and coated AA6063 alloy in a simulated marine environment and the polarization tests were compared to samples immersed during 30 days in same electrolyte solution. The obtained inhibition corrosion efficiency of the proposed coating system was measured comparing the Rp of the uncoated alloy to the coated samples, showing an efficiency about 99% for a 3% NaCl electrolyte for some of the samples. Therefore, the experimental results obtained during this research demonstrates the feasibility of using the developed anticorrosive composite coating to protect aluminum alloys against chloride corrosive ions species and to further continue with the corresponding research.