Example of an Application of an Assessment Procedure for Defects in Plant Operating in the Creep Range

Abstract

A worked example is presented to illustrate the application of a CEGB procedure for the assessment of defects in plant that operates within the creep range. The example chosen is a large cylindrical pressure vessel with a fully circumferential crack for which experimental results are available. The example demonstrates that it is straightforward to perform the calculations required in the procedure for the time for structural failure by continuum damage mechanisms, the time for crack incubation and the time for crack growth. It is predicted that crack incubation in the pressure vessel occurs at about one-third of life with the remaining life being taken up by crack growth. The predictions are in close agreement with the experimentally observed incubation, growth and final failure times.

Limit loads of circumferentially flawed pipes and cylindrical vessels under internal pressure

“…7. For f/1 the fully circumferential solution in [5] is recovered. The difference between FEM and the formulae for small cracks indicates the numerical error of the FEM.…”

“…Ainsworth and Coleman derived a lower bound limit pressure with the Tresca yield function for pipes with exterior fully circumferential surface cracks [5]. Jones and Eshelby have extended the method to internal cracks [6].…”

“…The limit loads for thick pipes in [5,6] for circumferential defects, based on the complete stress state, have been widely ignored, because they have been derived with the unrealistic assumption of a symmetric configuration of two opposite cracks. Primal-dual limit analyses with the finite element method (FEM) show that the formulae can be modified so that they give good predictions of global collapse loads for exterior and interior cracks.…”

Low temperature creep crack growth in low alloy reactor pressure vessel steel

“…For instance, t in takes up more than 50% of total lifetime at 320°C and about 20-30% of total lifetime in the most cases at other tested temperatures. Although the calculated t in is reported elsewhere [12,17,18], t in in the present study is empirically determined, see also Section 4.2. Empirically determined t in has also been given in [5,19].…”

Assessment of notched tubular ferritic oxide-dispersion-strengthened components subjected to multiaxial creep loading at 1100°C

“…The deepest measurement on each notch was used in calculating the reference stress. The notch depth to wall thickness ratio (a/t) in each case was greater than 0.5 enabling the load limit reference stress solution proposed by Ainsworth and Coleman [8] to be used such that…”