T91 steel pipes were investigated by series impact tests of T91-steel-made high temperature reheater pipes which had been running for 130 000 hours

combined with test results of the original pipes and T91-steel samples which had 60 000 hours of operation.Results show that

with the increasing running time

fracture appearance transition temperatrue(FATT) of T91 steel rose obviously

this indicates that there is a decrease in ductility and toughness of material during the running.After long time(130 000 h) operation at high temperature

T91 steel presents 100% shear fracture on the impact fracture surface when the test temperature was above 0 ℃

and the ductile fracture dominates.During the crack propagation process

only stable crack growth occurs

this is consistent with the cleavage fracture rate of the fracture surface(which is 0).As the temperature of impact test rising

crack propagation energy Wp of all 3 samples increases

and the original pipe's is the maximum when its test temperature is the same as the other two.