Time-Dependent Fracture and Defect Assessment of Welded Structures at High Temperature

The present work reports several new insights into creep crack growth performance and defect assessment of welded structures at elevated temperature. First of all, an equivalent homogeneous model based on the limit load analysis is proposed to reflect the mismatch effects of the base and weld metals, the geometrical dimension of weldment constituents and the location of the pre-existing defects. Secondly, using the proposed equivalent homogeneous model, an estimation methodology for the time-dependent fracture mechanics parameter $C*$ is developed in conjunction with the reference stress (RS) method and the GE/EPRI scheme. Such an estimation method was validated by using nonlinear finite element analysis of 48 compact tension (CT) specimens with various degrees of mismatch in creep behavior and different width of the welding seam. After that, the applicability of $C*$ measurement recommended in ASTM E 1457 is re-examined for the CT specimen with a mismatched cross-weld. From the limit load analysis, a series of modifications for experimental $C*$ estimation equation from ASTM E 1457 is introduced based on the proposed equivalent homogeneous model. Finally, a failure assessment diagram (FAD)-based method is presented for the welded structures at high temperatures. The application of such an approach to a welded cylinder with an internal circumference crack under axial tension is also reported in this paper.