Failure analysis and prevention of corrosion occurring during storage on steam generator tube sheet for advanced PWR, Part II: Corrosion prevention design

Abstract

During the manufacture of large nuclear equipment like steam generator, the components have to be stored in situ in the factory for several months, even over one year. In this circumstance, uniform corrosion is prone to attack the components like forges, shells and tube sheet etc. that are usually in large size and fabricated with carbon steels and low-alloy steels for a better cost performance ratio. Thus, corrosion prevention is required. In this paper, such a case regarding determination of the effective corrosion prevention methods is addressed. The component involved was the tube sheet of the steam generator of an advanced pressurized water reactor under construction, and its tens of thousands of drilled holes were found corroded in the intermittent storage periods during the manufacture. In the first part of the two companion papers, root causes analysis and mechanisms discussion was carried out on the corrosion; while in the current paper as the second part, a variety of corrosion prevention treatments was designed and their effectiveness was compared for choosing the optimal one. Based on the results of the two simulation tests including the salt mist test and the damp heat cyclic test, the two corrosion prevention treatments that both utilized the super desiccant were finally determined to rank the top two of the totally thirteen treatments we designed. Consequently, the role of relative humidity in initiation of uniform corrosion was discussed in detail, and such two treatments were recommended to the manufacturer and were immediately implemented. Till now (after half a year), they have been proved really effective, and are planned to be applied to other large-sized components in that factory.