Creep behaviour and lifetime of large welds in X 20 CrMOV 12 1—results based on simulation and inspection

Weld creep performance in steam lines of X 20 CrMoV 12 1 (X20) has been studied by simulation and plant inspection. By finite-element simulations, the influences of (i) the heat affected zone creep rate, (ii) the material constant α, related to the multiaxial rupture criterion, and (iii) axial system stresses on creep life, have been studied. The results show that an increase of each factor (i)-(iii) reduces the creep life, especially when two of them act at the same time. The inspection study covers over two decades of replica inspection of steam line welds in Danish power plants with service times up to 190.000 h. Analysis of the results shows that large butt joints and T-butt joints in X20 perform exceptionally well. They are unlikely to develop detectable creep damage within service times up to 200.000 h. One of the reasons for this good performance of the steel is its high time safety margin.