Hydrogen effects on high strength pipeline steels

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Hydrogen effects on high strength pipeline steels

Xie, Jeffrey / Yang, Lin / Worthingham, Bob / King, Fraser

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). Temperature is found to be an important parameter influencing the polarization resistance, solution resistance, hydrogen generation and the effect of hydrogen on the mechanical properties. For both X100 and X65 steels, polarization resistance is low and similar in values at temperatures above the freezing point, while increasing more than ten (10) times with only 4 deg C difference from 1 deg C to -3 deg C. In general these two steels behave similarly in terms of electrochemical properties for all the temperature spectra. Under freely corroding conditions, the generation rate of hydrogen is small. 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 increasing cathodic polarization.