Corrosion under insulation or CUI is a large problem for the owners of plants. Our client, BP Refinery Rotterdam, also struggled with this problem. Due to poorly functioning insulation and large fluctuations in temperature, an ideal climate is created for the corrosion process. Moreover, owing to the insulation, the surface is hidden from view, so that inspection of pipes and equipment for corrosion is often quite difficult. In order to ensure the integrity of the installation, comprehensive maintenance is necessary. BP recognized this long ago and therefore carries out an extensive CUI program.