Patent Number: 052271242
Section: claims

1. A method for preventive maintenance of an elongated metal hollow member welded to a wall of a pressure vessel of a nuclear reactor through a padding weld formed on said wall and extending into a coolant within said pressure vessel, said method comprising the steps of: removing said coolant from said hollow member;  smoothing an inner peripheral surface of a wall portion of said hollow member corresponding to said padding weld;  locating a stainless steel sleeve on said inner peripheral surface of said wall portion in a coaxial relationship;  fitting said sleeve onto said inner peripheral surface of said wall portion along an entire length of said sleeve; and  heating said sleeve through so as to produce a 4% by wt. or more .delta. ferrite molten metal portion penetrating into both said wall portion and said metal sleeve. 2. A method according to claim 1, wherein the step of heating is conducted by an electric arc welding. 3. A method according to claim 2, wherein the step of heating is conducted by heat sink welding. 4. A method according to claim 1, wherein the step of heating is carried out while cooling said wall portion. 5. A method according to claim 4, wherein said cooling is conducted by said coolant within said pressure vessel. 6. A method according to claim 2, wherein the step of heating is conducted using a non-filler tungsten inert gas welding machine. 7. A method according to claim 2, wherein said fitting of said sleeve is conducted by intermittently supplying current to said metal sleeve, thereby expanding with heat an outer periphery of said sleeve to fit said sleeve into said wall portion of said hollow member, and wherein said heating is conducted by supplying current to an electric arc welding machine in an inverted relationship to said current supplied to said sleeve. 8. A method according to claim 1, wherein the step of fitting of said sleeve includes enlarging said sleeve radially outwardly. 9. A preventive maintenance structure of an elongated metal hollow member welded to a wall of a pressure vessel of a nuclear reactor through a padding weld formed on said wall, a stainless steel sleeve fitted to an internal surface of said metal hollow member, and a 4% by wt. or more .delta. ferrite molten metal portion provided at a portion of an inner peripheral surface of said hollow member which corresponds to said padding weld, wherein said molten metal portion penetrates into both said wall portion and said sleeve.