Long-term creep rupture properties of TP347 H tube at 600 ℃ and 650 ℃ has been investigated by using the creep rupture data obtained from NIMS Creep Date Sheets. The influence of data scattering and C value in LM parameter on estimation reliability has been discussed. The test temperature range is 600～750 ℃ and the maximum time to rupture is about 210 000 h. The results show that

compared with other austenitic steels

TP347 H steel exhibits an obvious heat to heat variation phenomenon in creep rupture property. Under conditions with the same temperature and stress

creep life difference between the strongest and weakest heats can reach about one order of magnitude or more. Data points in adjacent temperature zones overlap partially. Therefore

the durability evaluation of TP347 H steel should be carried out in batches. When using the LM method to carry out long-term persistence energy extrapolation

compared with the C-value obtained by data fitting optimization

the C value obtained by its definition can greatly reduce the tendency of overestimation.