690 alloy has excellent resistance to intergranular corrosion and intergranular stress corrosion cracking, and is mainly used in pressurized water nuclear power plant steam generator heat transfer tube material. Pressurized water reactor nuclear power plant steam generator heat transfer pipe materials have gone through a development process, including 304 austenitic stainless steel,600 alloy, 800 alloy and 690 alloy. The study on corrosion failure of 600 alloy in service shows that intergranular corrosion and intergranular stress corrosion cracking are the main problems. 690 alloy as a pressurized water reactor nuclear power plant steam generator heat transfer tube material, since the 1990s has been put into use has not been found damaged reports.
Cap end is a component of the container, which is connected to the cylinder by welding. According to different geometric shapes,it can be divided into spherical, elliptical, dish-shaped, spherical crown, cone shell and flat cover. Among them, spherical,elliptical, dish-shaped and spherical crown heads are collectively called convex heads. In terms of welding, it is divided into butt welding heads and socket welding heads. It is used in various container equipment, such as storage tanks, heat exchangers,towers, reactors, boilers and separation equipment. The materials include carbon steel (A3, 20#, Q235, Q345B, 16Mn, etc.),stainless steel (304, 321, 304L, 316, 316L, etc.), alloy steel (15Mo3 15CrMoV 35CrMoV 45CrMo), aluminum, titanium, copper, nickel and nickel alloys.