Sulfide stress cracking of X70 pipeline steels

The X70 pipeline steels with different chemical compositions and welds were discussed in this paper,the effect of stress relieving by annealing on resistance of SSCC (Sulfide Stress Corrosion Cracking) was also studied.Testing results revealed that the properties of SSCC for pipeline steels are mainly influenced by Mn、P,not by C.It suggested that Mn、P play a key role in resistance of SSCC properties.With the increase of Mn and P contents,not only the microstructure formed at low temperature and inclusions will increase but also the integration of hydrogen atoms will be inhibited,leading to hydrogen embitterment.All these factors will decrease the resistance of SSCC of the pipeline steels in medium including H₂S.Moreover,stress relieving by annealing can improve the resistance of SSCC for pipeline steels.