A creep crack growth life assessment method for pressurized pipes based on a two-parameter approach

Abstract

The unified creep constraint parameter Ac based on crack tip equivalent creep strain can incorporate both in-plane and out-of-plane constraints in specimens and components. To improve the accuracy of creep crack growth (CCG) life assessment for cracked components, it needs to develop new life assessment procedures to consider the unified constraint. In this work, the methodology of the CCG life assessment based on two-parameter C*-Ac has been studied and given for pressurized pipes with a wide range of initial crack sizes. The assessment results of CCG life and crack size/shape evolution based on the two-parameter C*-Ac approach are quantitatively analyzed and compared with those based on the conventional single-parameter C* approach. The effects of calculation methods of C* on the CCG life assessments are also analyzed. The results show that the application of the two-parameter approach can reduce conservatism and predict reasonable crack growth size and shape. The conventional CCG life assessment based on the single-parameter C* and the reference stress C* calculation for shallower and shorter surface cracks with lower constraint in cracked pipes may produce very high overall conservatism degree. Therefore, in the CCG life assessments for these cracks, it is highly suggested that the constraint effect is considered and the finite element solution of C* is used.