Potential hazards from undetected corrosion in complex equipment: A case study of the destructive separation of an offshore heat exchanger

This paper describes hazards from undetected corrosion in complex equipment using findings from a collaborative forensic investigation into the destructive separation of a heat exchanger on an offshore gas storage platform. The heat exchanger had been in service for 24 years. The heat exchanger was a conventional shell-and-tube type with both the tubes and shell being manufactured from titanium. However the bonnet and tube sheet were manufactured from carbon steel. The seawater side of the carbon steel tube sheet had been protected from corrosion by titanium cladding. vestigation revealed localised corrosion of the carbon steel tube sheet in areas exposed to acidic condensate containing hydrogen sulphide. Corrosion was galvanic in nature and had occurred where, by design; the carbon steel–titanium interface was exposed. The results showed that hydrogen, generated cathodically by the galvanic corrosion, had formed titanium hydride in the interfacial region of the titanium cladding. idence indicated that the separation of the tube bundle and shell from the bonnet was probably initiated when a large area of the cladding bond interface failed suddenly due to hydride formation. The final destructive separation of the tube bundle can be explained by the deformation of the cladding after complete failure of the bonded interface with the tube sheet. rticle and the forensic investigation were funded by the Health and Safety Executive (HSE). Its contents, including any opinions and/or conclusions expressed, are those of the author alone and do not necessarily reflect HSE policy. The UK Health and Safety Executive funded this paper to draw attention to the potential hazards that can arise from undetected corrosion in complex equipment.