Breakdown of heat exchangers due to erosion corrosion and fretting caused by inappropriate operating conditions

Damage analyses on two heat exchanger units showed that in both cases inappropriate flow conditions of media caused very different failure mechanisms that resulted in irreparable damage. The first incident was the breakdown of an unalloyed steel condenser, which operated in a coal-fired power plant. A considerably high number of tubes successively leaked. Metallography identified lines of segregation in the microstructure of the tube walls, thus, giving evidence that both uniform corrosion and erosion corrosion caused by low-pressure wet steam were the root cause. The second incident was the breakdown of a recuperator made from chromium–nickel steel due to mechanical damage to tubes and baffle. This unit operated as part of a pilot plant to regain heat from the drying process of sewage sludge. It turned out that soiled vapour caused clogging of the cross-sectional area and therefore accelerating the flow velocity of the vapour. This inappropriate operating condition caused the tubes to oscillate so severely that they even banged together. Abrasive wear especially at the intersection through the holes of the baffle damaged the tubes and the whole unit irreparably.