Corrosion Of Heat Exchange Tube For PWR Steam Generators

Steam Generator (SG) is one of the most important equipments of Pressurized Water Reactor (PWR) nuclear power plant. SG heat exchange tubes are the pressure boundary of primary coolant, whose integrality has great impact on operation safety of nuclear plant. Therefore, the materials for SG heat exchange tubes must meet stringent technical requirements, among which resistance to the corrosion in primary and secondary coolant corrosion is of the greatest concern. Nickel base alloy 690TT and alloy 800 are considered to be the best selection for making SG heat exchange tubes.Intergranular corrosion, pitting and stress corrosion cracking of alloy 690 specimens with different heat treatment process were evaluated according to ASTM G28, G48, G61 and also in boiling 50%NaOH solution. Scanning electron microscopy (SEM) was used to analyse the surface corrosion morphology. Corrosion resistance of Alloy 800 with and without surface shot peening was also studied by the similar methods as that used for alloy 690.The results show that, corrosion resistance of alloy 690 is improved remarkably after proper solution and thermal treatment process. The grain size of alloy 690 increases with the increase of solution treatment temperature (1060℃～1140℃).The effect of surface shot peening on pitting corrosion resistance of alloy 800 tube has been investigated using electrochemical cyclic polarization curve and soaking in FeCl3 solution. The results showed that the pitting weight loss of shot peened specimen is higher than specimens without shot peening. SEM observation found that the pits specimens without shot peening were bigger in area and shallower in depth than those shot peened.