CREEP LIFE PREDICTION USING CREEP TESTS AND OMEGA METHOD: PRACTICAL APPLICATION TO A 2.25CR-1MO STEEL

In this research, creep tests were carried out on ex-service 2.25Cr-1Mo steel under conditions more severe than those of service. The specimens were tested in a temperature range of 585 degrees C up to 650 degrees C and in a stress range of 65 MPa up to 120 MPa, leading to strain rates values of the order of 10(-5) h(-1). Conventional creep rupture tests and stepped tests (isothermal and multiple load levels) were conducted. The results of these tests are presented in terms of rupture time and the Omega method parameters Omega, and (epsilon) over dot(0). The implementation of the Omega method, testing methods and the test conditions are then discussed together with the values of the parameters Omega and (epsilon) over dot(0) obtained. Those values were compared to the corresponding values from API579-1 data base [1] and the adjustment factors Delta(Omega)(cd) and Delta(Omega)(sr). Lifetime prediction of the Omega method and the importance to identify the material scatter parameters for a given metallurgical condition are discussed.