2016:28 Fatigue fracture surface characterization and investigation


In a previous study (SSM research report 2015:38) fatigue experiments were performed on welded austenitic stainless steel piping components. The fatigue experiments offer an opportunity to examine the obtained fatigue cracks with an optical microscope.


The present study performs a fractographical examination of the obtained fatigue cracks with the aim of determine where fatigue cracks initiate and how the fatigue cracks propagate in the welded austenitic stainless steel pipes.


The study has increased the understanding of fatigue critical points in welds, as well as it has increased knowledge on where fatigue cracks initiated and how propagation occur in the welded austenitic stainless steel pipes. The main results from the study are:

  • Fatigue cracks were initiated from both the inside and outside of the
    weld joint.
  • Fatigue initiation from the outside of the weld joint (weld toe) occurred predominantly at low cycle fatigue.
  • Fatigue initiation from the inside of the weld joint (weld root) occurred predominantly at high cycle fatigue.
  • High cycle fatigue life was not affected by the presence or the quality of the weld cap since the fatigue cracks started from the weld root.