Experimental investigation of specimen size effect on creep crack growth behavior in P92 steel welded joint

• Effect of constraint induced by specimen size on creep crack growth was studied.
• Even in low constraint specimen FGHAZ showed a fast creep crack growth rate.
• Correlation of C* with creep crack grow rate depended on specimen thickness.
• Creep crack growth rate accelerated with increasing specimen size.
• Constraint effect should be incorporated into normal remained life prediction.

In order to clarify the effect of constraint induced by specimen size on creep crack growth behavior of P92 steel welded joint, creep crack tests were carried out on the compact tension specimens with thick thickness and thin thickness, the crack tip of which were located at different distinct zones of welded joint. Tested results revealed that even in thin thickness specimens, fine grained heat affected zone specimens exhibited a fast creep crack growth rate compared with other micro-zones specimens due to a low creep crack resistance and a high multistress state. The fractographies of these specimens exhibited an accelerated number of spherical particles that were caused by the coalescence of creep voids. Furthermore, the correlation of C* with creep crack growth rate was dependent on specimen thickness. As the specimen thickness increased from 10 to 30 mm, the creep crack growth rate increased. This was due to the increase in constraint level ahead of crack tip during creep crack propagation.