A two-parameter fracture criterion has been proposed to predict fracture conditions of notched components. This criterion includes the critical notch stress intensity factor K ρ,c , which represents fracture toughness of a material with a notch of radius ρ, and the effective T -stress. The effective T -stress T e f has been estimated as the average value of the T -stress distribution in the region ahead of the notch tip at the effective distance X e f . These parameters were derived from the volumetric method of notch fracture mechanics. The results of numerical T e f,c -stress estimation are compared to the T e f,c -stress results obtained from experimental analysis. The material failure curve or master curve K ρ,c = f T e f,c has been established as a result of the notched specimen tests. A large T e f,c range was covered from −0.80 σ Y to +0.19 σ Y using SENT, CT, RT (roman tile) and DCB specimens. It was shown that the notch fracture toughness is a linear decreasing func-
The following cases of hydrogen influence on pipeline metal were considered: gaseous hydrogen under internal pressure in notched pipes and electrochemically generated hydrogen on external pipe surface from soil aqueous environment. The burst tests of externally notched pipes under pressure of hydrogen and natural gas (methane) were carried out after the pipe has been exposed to a constant ''holding'' pressure. It has been shown that even for relatively ''soft'' test conditions (holding pressure p ¼ 20 bar and ambient temperature) the gaseous hydrogen is able to penetrate into near surface layers of metal and to change the mechanism of local fracture at notch. The sensitivity to hydrogenating of given steel in deoxygenated, near-neutral pH NS4 solution under soft cathodic polarisation was studied and the assessment local strength at notches in pipeline has been made for this conditions. Here, the relationship between hydrogen concentration and failure loading has been found. The existence of some critical hydrogen concentration, which causes the significant loss of local fracture resistance of material, was also shown.
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