Abstract
The seismic condition for nuclear power plant has been becoming severe more and more. It certainly influences the seismic design of nuclear power plant piping. Especially, the seismic evaluation for tee is very severe but the evaluation contains margin. So the margin in primary stress evaluation of tee was investigated by the comparison with the evaluation by limit analysis. As a result, it turned out that the primary stress evaluation and its stress indices are basically appropriate for entire evaluation under various load condition on tees. But it also turned out that the detail load condition of tees should be considered to obtain more detailed and reasonable evaluation.
