Metallurgical investigation of a heat-exchanger tube of 70/30 cupronickel failed by fretting corrosion

•A heat-exchanger (cupronickel tubes, mild steel baffles) showed leakage in a tube.•Thinning of the tube had occurred from the OD side only at baffle locations.•Loose debris of magnetite and adherent CuO detected on the tube OD surface.•Deformation of tube at baffles, reflected by deformed grains and hardness increase.•Failure of the tube was concluded to be caused by fretting corrosion.