Influence of Long-term Annealing and Hot Bending on Creep of P92 Pipe

Abstract

This work is focused on the creep behaviour of the thick-walled hot bended P92 pipe, with an outer diameter of 350 mm and wall thickness of 39 mm, in its dierent parts, namely in straight parts and bends. Selected creep specimens machined from axial section of pipe were thermally aged at 650• C to simulate microstructure degradation typical for long-term service conditions. Subsequent tensile creep tests at constant load were performed at 600• C under 140 MPa and creep behaviour of various structure states was compared. Microstructure was investigated by scanning electron microscopy equipped with electron backscatter diraction. It was found that ageing at 650• C for 10 4 h caused the signicant reduction of creep resistance down to about 10% of initial state and an additional slight reduction of creep resistance after longer ageing for 2 × 10 4 h. Further, creep behaviour was signicantly inuenced by specimen position in the extrados and intrados parts of bends. Microstructure investigation revealed that long-term annealing has negligible eect on high-angle grain boundary spacing and misorientation. By contrast, creep deformation of long-term annealed specimens led to signicant decreasing in high-angle grain boundary spacing and caused a change in the misorientation distribution of boundaries.