This paper describes a newly developed 3D polycristal elasto-viscoplasticity FEM code that can deal with creep damage in the form of creep voids in a welded modified 9Cr-1Mo steel plate. Creep voids are often found in HAZ in the steel especially in long-term creep region of, say, 100,000 hr or longer where creep rupture lives become much shorter than predicted by extrapolating the creep rupture curve in the shorter creep life region. The present author and his colleagues have been developing 2D FEM codes of the combined polycrystal elastoviscoplasticity and isotropic damage analysis to analyze internal creep damage or cracking in HAZ called Type IV damage in a weld joint of modified 9Cr-1Mo steel plate. This study has three-dimensionalized the FEM code, and also has developed and implemented efficient solvers to make effective computation and to improve CPU time, since the CPU time is explosively increased for 3D calculations. The results obtained by the present FEM analyses showed that creep damage is localized and considerably enhanced in HAZ regions and that the resultant creep rupture curve agree well with those obtained by experiments.

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