A downhole installation comprises: a first pipe layer 8, a second pipe layer 10 about the first pipe layer 8, an annulus 12 between the first pipe layer 8 and the second pipe layer, and a geological formation outside of the second pipe layer 10. A method for evaluating the downhole installation comprises: exciting a flexural wave in the first pipe layer 8 using an angled acoustic transmitter 20; receiving third interface echo data using a plurality of angled acoustic receivers 14, 16 at different locations along the longitudinal extent of the pipe layers 8, 10; generating acoustic resonance across the thickness of the first pipe layer 8 and the second pipe layer 10 by use of full waveform excitation; receiving the acoustic response wave field generated by the full waveform; identifying a suitable component of the acoustic response wave field as being representative of the material state behind the second pipe layer 10; determining, based on the amplitude of the identified component and a suitable threshold value, if the material outside the second pipe layer 12 is fluid or solid; and analysing the third interface echo data in light of the determined material state in order to thereby evaluate material conditions in the annulus 12 outside the second pipe layer 10.