Fracture toughness of welded joints materials for main pipelines at Ignalina NPP

Abstract This paper deals with an investigation of mechanical and fracture toughness characteristics of welded joint materials used in Ignalina Nuclear Power Plant (NPP) reactor main circulating circuit (MCC) and steam pipelines. Basic metal of MCC group distributing header (GDH) steel 08Ch18N10T (Du-300), its weld metal welded by manual and automatic arc method using the wire SV-04Ch19N11M3 and electrodes EA-100/10U or EA-100/10T, this joint heat-affected zone metal and base metal of the main steam system—steel 16GS (DU-630) and its weld metal welded by manual arc method using the wire SV-08GS2 and electrodes UONI-13/55 were tested. Mechanical properties of welded joints materials—proportional limit (σpl), yield (σy) and ultimate (σu) strength, fracture stress (σf) and ductility (Z) (percent reduction of area) of the specimens were determined. Investigation of relative critical stress intensity factor for fixed thickness of the specimen K C * and critical J-integral, JIC, was performed. The probabilistic investigation of influence of the mechanical properties (σpl, σy, σu) onto fracture toughness characteristics K C * and JIC for tested materials by using linear regression model with three independent variables was performed. Research enabled to conclude that proposed multivariable regression model with 80% probability (confidence coefficient α = 0.05) has explained reasonably well the dependence of K C * with σpl, σy, σu and it has shown the non-acceptability of probabilistic evaluation of the model with respect to JIC.