Corrosion Performance Evaluation Of Heat Exchange Tube For PWR Steam Generators

Steam Generator (SG) is a very important heat exchange equipmentof a Pressurized Water Reactor (PWR) nuclear power station. As theheat exchange interface between the primary loop and the secondaryloop, heat transfer tubes form the largest part of primary pressureboundary. In order to meet the needs of long-term operation, SG heattransfer tube must has excellent corrosion resistance property at thecondition of the PWR operating temperature and the water chemistrayenvirement of primary loop and secondary loop. Currently, alloy600TT,alloy690TT and alloy800Mod are commonly used to make heatexchange tubes. Among them, alloy690TT and alloy800Mod areconsidered the best choices for producing SG heat transfer tube.In this paper, the stress corrosion cracking (SCC) performance ofalloy690TT in the water chemistray environment containing20ppb zincand containing0ppb zinc were researched by using slow strain ratetesting experiment. General corrosion, intergranular corrosion, pittingcorrosion, high temperature and concentrated NaOH stress corrosioncracking performance of alloy800Mod specimens with and without surface shot peening were tested by using chemical method,electrochemical method, static autoclave experiment, high temperatureand concentrated NaOH stress corrosion cracking method. Finally, weget the surface morphology of specimens after corrosion with scanningelectron microscopy (SEM) and optical microscope.The experiment results show that, alloy690TT specimens in thewater chemistray environment containing20ppb zinc or containing0ppbzinc have no susceptibility to stress corrosion cracking. However, in the20ppb zinc environment,690TT specimens absorb more energy beforefracturing. It means that zinc is useful for alloy690TT to resist the SCC.The static autoclave experiment in the environment simulatedsecondary loop of PWR (10%NaOH solution) results show that, surfaceshot peening is useful for alloy800Mod to resist the high temperatureand concentrated NaOH stress corrosion cracking. However, afterexposed in the environment simulated PWR primary loop3000h, thecorrosion wight loss rate of alloy800with shot peening is high,4.896mg/dm2. It means that the surface shot peening can make thegeneral corrosion weight loss rate increased. We also find that surfaceshot peening can lead to the degradation of alloy800’s performance to resist pitti ng corrosi on and intergranular corrosi on.