Influence of stress triaxiality on hydrogen assisted ductile damage in an X70 pipeline steel

The presence of hydrogen in steel components affects their structural integrity through a phenomenon called hydrogen embrittlement. While it is known that hydrogen affects the mechanical damage development upon loading, the specific mechanisms are still unclear. An experimental study is presented that investigates the plastic anisotropy and ductile fracture behavior of API 5L X70 pipeline steel with and without hydrogen charging at multiple scales. Three different tensile test specimen geometries (smooth and notched axisym-metric) are employed to investigate the influence of stress triaxiality thereon. The macromechanical responses during tensile tests are analyzed, along with micromechanical features of the resulting damage obtained using High-Resolution X-ray Computed Tomography. For all stress triaxialities tested, the presence of hydrogen does not affect the macroscopic plastic anisotropy, but accelerates ductile damage development and fracture, which is in agreement with the plasticity dominated hydrogen embrittlement mechanisms HELP and HESIV. Increasing stress triaxiality leads to a larger susceptibility to hydrogen embrittlement. Hydrogen accelerated void nucleation and enhanced lateral void growth are observed and quantified. The presented results can aid the development of numerical models describing hydrogen embrittlement in high-strength low-alloy steel.

Automated summary

An experimental study was conducted to investigate the plastic anisotropy and ductile fracture behavior of API 5L X70 pipeline steel with and without hydrogen charging. The presence of hydrogen was found to accelerate ductile damage development and fracture, especially under higher stress triaxiality. These results are important for the development of numerical models to describe hydrogen embrittlement in high-strength low-alloy steel.