The need for microalloyed steels resistant to harsh environments in oil and gas fields, such as pre-salt which contain considerable amounts of hydrogen sulfide (H2 S) and carbon dioxide (CO2 ), requires that all sectors involved in petroleum industry know the factors that influence the processes of corrosion and failures by hydrogen in pipelines and components fabricated with microalloyed steels. This text was prepared from a collection of selected publications and research done at the Electrochemical Processes Laboratory of Metallurgical and Materials Engineering Department, Polytechnic School, Sao Paulo University. This document does not intend to be a complete or exhaustive review of the literature, but rather to address the main scientific and technological factors associated with failures by hydrogen in the presence of wet hydrogen sulfide (H2 S), particularly, when related to the Hydrogen Induced Cracking (HIC) phenomenon. This complex phenomenon that involves several successive stages, HIC phenomena were discussed in terms of environmental and metallurgical variables. The HIC starts with the process of corrosion of steel, therefore must be considered the corrosive media (H2 S presence) effect. Moreover, it is necessary to know the interactions of compounds present in the electrolyte with the metal surface, and how they affect the hydrogen adsorption and absorption into steel. The following stages are hydrogen diffusion, trapping and metal cracking, directly related to the chemical composition and the microstructure, factors that depend strongly on the manufacture of steel. The purpose of this paper is to provide the scientific information about the failures caused by hydrogen and challenge for the Oil and Gas Pipeline Industry