Susceptibility of a X80 steel to hydrogen embrittlement

Abstract

The susceptibility to hydrogen of a X80 grade steel produced by a thermo-mechanical control process (TMCP) has been investigated by keeping straining notched specimens under continuous charging conditions. Hydrogen charging was carried out either in synthetic seawater under potentiostatic control at À 1000 mV vs. SCE or in sulphuric acid with an absorption promoter under galvanostatic control at À 5 mA/cm 2 .Results reported in terms of hydrogen effect on the ductility of the steel as a function of both cross head speed and root radius of the notch indicate that under the combined effect of cathodic charging, notch severity and very low strain rates the ductility of the TMCP X80 steel can be greatly affected by the presence of hydrogen.With notched specimens strained in air increasing loss of ductility in terms of reduction in area is observed as the notch severity increases. Notched specimens are fairly "more brittle" than smooth ones. As notched specimens are strained under cathodic charging at À 1000 mV vs. SCE in the synthetic seawater, considerable decrease of reduction in area (RA) is observed. The same trend is observed for displacement and load at fracture both being connected with ductility even if a definite tendency is not always obtained.As the notched specimens are strained under cathodic charging in seawater the fracture morphology shows regions of mixed ductile and brittle fracture and zones where intergranular and/or transgranular fracture path are prevailing. Area of intergranular and transgranular fracture path, that can be more strictly associated with the presence of hydrogen, tends to increase as the strain rate decreases, which suggests a fracture behaviour influenced by hydrogen diffusion.Several mechanisms were involved in the rupture process in sulphuric acid depending on the notch geometry and, especially, on the cross head speed. Apparently, transgranular (quasi-cleavage) rupture tends to prevail as the displacement becomes lower and lower. No evidence of intergranular fracture was observed.

Electrochemical corrosion behavior of X80 pipeline steel in a near‐neutral pH solution

“…It has been demonstrated [14,31,32] that hydrogen-charging would enhance the anodic dissolution of the steel. Therefore, the size of the semicircle in EIS plots, which is associated with the chargetransfer resistance of corrosion reaction, decreases with the hydrogen-charging current density, as seen in Fig.…”

Hydrogen embrittlement susceptibility of a high strength steel X80

“…In order to reduce the cost of production of pipelines, directly related to the quantity of metal needed, high strength steels are used such as X80 for natural gas. However, previous workers have shown that many high strength steels are susceptible to hydrogen embrittlement, inducing degradations of the mechanical properties [1][2][3]. The purpose of this study is both to assess the specific resistance of X80 to hydrogen embrittlement and to contribute to an improvement of the understanding of hydrogen effect on high strength steels.…”

Fatigue crack initiation and growth in a CrMo steel under hydrogen pressure

“…The presence of a defect (hole, notch) on specimen increases the stressconcentration and modifies the hydrostatic stress in the process zone ahead of the defect, influencing locally the hydrogen content [9,10]. It also changes the local loading.…”