Net-section limit moments for circumferential cracks at the interface between elbows and pipes

Closed-form net-section limit moment solutions are given for circumferential through-wall and part-through surface cracks at the interface between elbows and attached straight pipes under in-plane bending, via systematic, small strain FE limit analyses using elastic-perfectly plastic materials. Net-section limit moments for circumferential cracks at the interface between elbows and attached straight pipes are found to be close to those for cracks in the centre of elbows, implying that the location of the circumferential crack within an elbow does not affect net-section limit moment. Moreover, when a crack in welds between an elbow and attached straight pipe is assessed, the assumption that the crack locates in a straight pipe could significantly overestimate a net-section limit load (and thus maximum load-carrying capacity) of the cracked component, and thus could be non-conservative. For conservative assessment, a crack should be assumed to locate in the centre of an elbow, rather than in a straight pipe.