Relationship between fatigue crack growth behaviour and local hydrogen concentration near crack tip in pipeline steel

The work is dedicated to evaluation of fatigue crack growth rate in pipeline steel under hydrogenating conditions with taking into account of local hydrogen concentration near the crack tip. The measurement of local hydrogen concentration CH in metal was made by special technique of mass-spectroscopy with laser microprobe. It has been found that fatigue crack growth rate da/dN is the function of some critical combination of following parameters: local hydrogen concentration at the crack tip CH(t), hydrogen concentration in bulk of metal CH(v) and range of stress intensity factor ΔK. The application of derived formula for fracture risk assessment of defected pipeline is shown.