Failure crack character of φ273 mm x 22 mm main steam pipe of 12CrMoV steel (0. 12C
0. 45Cr
0. 31 Mo
0. 22V) serviced for 30 000 h under the condition of creep-fatigue interaction serviced al power station has been studied and analyzed. Results showed that the crack developed and spread along grain-boundary
and the stress concentration formed at oxide defect of steel tube surface induced by creep
existence of coarse carbide and thermal fatigue induced by high temperature impact load were main cause to form crack of inner surface of steel pipe.