The local mass transfer in a 203mm diameter back to back bend arranged in a S-configuration was measured at a Reynolds number of 300,000. A dissolving wall method using gypsum dissolution to water at 40°C was used, with a Schmidt number of 660. The experiment was performed in a flow loop by flowing water through the test section. The topography of the unworn and the worn inner surface was quantified using nondestructive X-ray Computed Tomography (CT) scans. The two scanned surfaces were aligned to a common coordinate system using commercial software and in-house routines. The local mass transfer rate was obtained from the local change in radius over the flow time. Two regions of high mass transfer were present: (i) along the intrados of the first bend near the inlet and (ii) at the exit of the extrados of the first bend that extends to the intrados of the second bend. The latter was the region of highest mass transfer in the S-bend.