Hydrogen Effects on High Strength Pipeline Steels

High strength pipeline steels are currently being considered for new construction and line extensions for economic reasons. These steels are designed for high strength and high toughness for fracture resistance. In this investigation, the electrochemical behavior, hydrogen permeation and hydrogen effect on mechanical properties were investigated. The testing was designed to simulate corrosion and hydrogen generation around the high strength steel (X100) under permafrost condition, with the comparison to the regular pipeline steel (X65 steel).

For both X100 and X65 steels, polarization resistance is low and similar in values at temperatures above the freezing point, while increasing abruptly and dramatically at temperatures below the freezing point. In general these two steels behave similarly in terms of electrochemical properties.  

Under freely corroding conditions, the rate of generation of hydrogen is small, while the application of cathodic protection increases the generation of hydrogen, especially at temperatures above the freezing point. As a result, both steels became less ductile with cathodic polarization. However for the condition of permafrost or temperature lower than 20°C, the ductility loss of X100 steel due to hydrogen permeation is comparable to that of X65 steel.