Fracture studies of straight pipes subjected to internal pressure and bending moment

• Fracture experiments are explained for three cracked pipes tested under pressure and bending moment.
• Experimental and finite element results are compared and found in agreement.
• Fracture toughness properties, J-R curves, are calculated from experimental results of pipes.
• Crack tip constraints are computed in terms of, Q, for pipes and TPB specimen.
• Variation in fracture toughness properties are explained in the light of respective crack tip constraints, Q.

Total three straight pipes have been studied which are used in the Primary Heat Transport system of Indian PHWRs (Pressurized Heavy Water Reactor). The pipes have been fabricated with either circumferential throughwall crack or surface crack. Fracture tests have been performed on these pipes subjected to constant internal pressure and monotonically increasing four point bending load. Different experimental and finite element results like load vs. load line displacement, load vs. CMOD (Crack Mouth Opening Displacement), crack initiation loads are compared and found in good agreement. The experimental results have been used for calculation of fracture toughness i.e J-R curves for all three pipes. The differences in these J-R curves have been investigated in the light of prevalent crack tip constraints. Higher J-R curve of surface cracked pipe is attributed to prevalent lower crack tip constraint and vice versa is true for throughwall cracked pipes.