The 690 alloy has excellent resistance to intercrystalline corrosion and intercrystalline stress corrosion cracking. The heat transfer materials for PWR steam generators have undergone a development process including 304 austenitic stainless steel, 600 alloy, 800 alloy and 690 alloy. The study of corrosion failure in service of 600 alloy shows that intergranular corrosion and intergranular stress corrosion cracking are the main problems. The 690 alloy has been used as the heat pipe material for steam generator of PWR nuclear power plant.