Study On Leakage Of Plate Type Heat Exchanger For Conventional Island Of Qinshan Phase II Nuclear Power Plant

Plate type heat exchangers are utilized as closed component cooling water system equipment in conventional island of Qinshan Phase II nuclear power plant due to their advantages of compact structure, high heat transfer rate, small space requirement and convenient maintenance. Field experiences showed that the plate type heat exchangers used in Qinshan plant increased the heat transfer efficiency greatly and simplified the maintenance work. However, high sand concentration in sea water causes the clogging at the sea water inlet and outlet holes of the heat exchanger plants, and increases the flow velocity at the remaining spaces, and thus causing high erosion wear rate of titanium plate. Penetration holes are easily formed at the locations where flow velocity is high, causing shut down of the heat exchanger.By analyzing the operation conditions of the plate type heat exchangers and mechanistic study of wear rate due to sand containing sea water, flow velocity due to clogging by sand in sea water has been recognized as the critical reason that causes the failure of plate type heat exchanger. Therefore, the study of effect of flow velocity and sand content on flow induced erosion wear rate of the heat exchanger plate is of great importance for defining a good operational procedure for heat exchangers in Qinshan plant. A testing system for experimental study of the flow velocity effect on wear rate was established, and tests were conducted to investigate the relation of flow velocity, sand concentration on wear rate of titanium plates. The results showed that when the flow velocity increased up to 6m/s, the weight loss of titanium plate increases dramatically. According to this result, the methods to mitigate the failure of plate type heat exchangers are proposed, in which the major measures are taken to reduce the clogging at sea water inlet and outlet. Periodical back flush of the heat exchanger is one of the important counter measure to reduce failure rate of titanium plates. And changing of the sea water screens is proposed as another good practice to reduce the sand and rubbish content in sea water, and therefore can greatly reduce the thinning rate of the plates. Failure rate of the titanium plates is reduced remarkably after the above practices have been applied in Qinshan plant for three years, thus greatly reduced the maintenance cost.