Reheat cracking is a creep failure mode that has been observed in welded structures operating at high temperatures in the power generation industry. The failure results from the initiation and growth of voids mainly at grain boundaries. A trial experiment has been performed using the D11 instrument at the ILL and the size distribution of creep cavities characterised in the size range 1-600nm. The present experiment will use the Sans2D instrument to measure scattering in the same test sample at same locations using the same 5mm diameter gauge area and also a second sample exposed to long-term ageing. The results will be analysed using the same maximum entropy routines applied to the D11 data and also using FISH. This will allow a direct comparison of scattering results from the two instruments building confidence in application of this technique to engineering applications.