Guided wave sensitivity to creep damage represented by effective material property variations using finite element modelling


In high temperature pipework the detection of creep damage is important to prevent catastrophic failure which may occur if creep cracks grow above a critical size. Current methods of non-destructively testing for creep damage can be either time consuming or difficult to apply in an industrial setting; there is a need for development of new or improved inspection techniques. Guided wave testing is a rapid long range inspection technique which is routinely used as a screening tool for defects such as corrosion in pipelines. Initial guided wave testing of pipes with suspected regions of creep damage has suggested that guided wave testing may be sensitive to creep damage. This was not initially expected as the scale of the individual creep pores is much smaller than the wavelength used in typical guided wave testing. In this presentation the geometry of creep voids in ex-service pipe samples is determined from macrographs of their cross section. In the long wavelength regime the effect of creep damage may be modeled as a change in the effective material properties of the pipe, which significantly reduces the computational complexity and allows the generation of full scale guided wave models. The effective properties of creep damaged material have been calculated by modeling the stiffness of a section of material with voids representative of the expected levels of creep damage. Utilizing finite element guided wave models the sensitivity of guided wave testing to localized regions of creep damage, modelled as a change in material properties, is then investigated.