Mechanical Properties and Notch Sensitivities of the Hydrogenated X70 Pipeline Steel Welded Joints

In order to explore the effects of pipeline inner-wall surface defects on reliability of the hydrogen enriched compressed natural gas(HCNG) pipeline steel welded joints in long-term service， the notches in the base metal， weld seam and heat affected zone of X70 pipeline steel welded joints were made，and the electrolytic hydrogen permeation on the notches was performed.Tests and analysis of the tensile mechanical properties， microstructures and notch sensitivities of the X70 pipeline steel welded joint notch samples with/without hydrogen permeation were carried out.Results showed that hydrogen permeation led to a decrease in the tensile mechanical properties of X70 pipeline steel welded joint samples， especially plasticity (elongation at break A).Due to the combined effect of notch and hydrogen damage， the tissue at the notch did not undergo significant deformation，and the tensile fracture exhibited quasi cleavage fracture characteristics.Furthermore，the welded joints of X70 pipeline steel with and without hydrogen permeation had certain notch sensitivity， and hydrogen permeation could increase the notch sensitivity of the welded joint.Therefore， the hydrogenated welding seams should be paid more attention during the pipeline maintenance， because of their higher notch sensitivity.