Evaluation of Hydrogen Embrittlement on Pipeline Steel Due to Cathodic Protection Overpotential

This project will be discussing about the hydrogen embrittlement(HE) failure mechanism under over potential cathodic protection of steel use for buried pipelines. The integrity of pipeline depends on the corrosion mitigation method of coating and cathodic protection. In general, coatings are use as the first barrier in protecting against the onset of corrosion in many situations. However, coatings are not perfect where it can cause corrosion to occur at the breaks or holiday. Basically Cathodic Protection(CP) is the most effective practices normally being applied to protect buried pipelines from corrosion. For this project, commonly use steel for buried pipeline which is carbon steel SA516 grade 70 will be assessed by applying cathodic protection on it. Its behavior will be evaluated through the hydrogen evolution produce and the mechanical properties. The carbon steel SA516 grade 70 will be exposed to the cathodic protection range from -700 mV to -1300 mV respect to silver silver chloride (Ag/AgCl) of reference electrode. These behaviors will be compare between the safe potential cathodic protection against the over potential of cathodic protection. Theoretically, over potential can lead the reduction of water to take place to the reaction. Due to the alkaline environment created, it will accelerate the corrosion to occur where can cause the hydrogen evolution to evolve. Generally, hydrogen is generated in neutral environment. Thus, the hydrogen evolution potential is depending on the pH. The higher of pH, leading to the higher of hydrogen evolution potential. Hydrogen atoms (H) or nascent hydrogen can either chain to form hydrogen molecules (H2) or penetrated into the metal matrix. This atomic hydrogen can cause blistering of the metal. Hydrogen embrittlement phenomenon also will exhibit to the loss of ductility at very low negative potential.