Brazing sleeve having ceramic flux band and method for applying same

A sleeved construction of connected, first and second sealed joints for spanning a defect, comprising:

• an elongated metal tube of generally cylindrical interior configuration of a given interior diameter and having an open end and a defect in the sidewall thereof, accessible from the open end thereof;
• a brazing sleeve of generally cylindrical configuration having first and second ends and a first annular recess in the outer cylindrical surface thereof adjacent said first end, said sleeve having an outer diameter approximating, but smaller than, the interior diameter of said metal tube throughout at least a substantial portion of its length including said first end thereof;
• a first braze preform initially received in said first annular recess of said brazing sleeve;
• a first ceramic flux band initially formed on a first circumferential surface portion of said sleeve contiguous to said first annular recess and disposed interiorly thereof, said ceramic flux band being formed by adhering a powder flux material on the circumferential surface portion and heating same sufficiently to melt the powder flux material to form an adherent, hard ceramic flux band;
• said brazing sleeve being positioned within said metal tube, by insertion through said open end thereof, to span said defect between said first ceramic flux band and said second end of said sleeve, said first circumferential surface portion of said sleeve being positioned beyond said defect, relative to said open end of said metal tube;
• at least said first end of said brazing sleeve being interiorly expanded and then heated to melt said first braze preform and said first ceramic flux band and form a first sealed joint between said first circumferential portion of said sleeve and said tube;
• and
• said second end of said brazing sleeve including means forming a second sealed joint between said sleeve and said tube.

a nuclear reactor system, comprising:

• a pressure vessel;
• a plurality of heat exchange tubes housed in said pressure vessel, each said heat exchange tube being of metal and having at least one open end and an elongated, generally straight axial portion extending from each such open end and having a sidewall defining a generally cylindrical interior of a given diameter;
• and
• a sleeve construction of connected, first and second sealed joints for spanning and bypassing a defect in the sidewall of a given said heat exchange tube located at a position in the straight axial portion of said tube displaced form a given, open end thereof;
• a brazing sleeve of generally cylindrical configuration having first and second ends and a first annular recess in the outer cylindrical surface thereof adjacent said first end, said sleeve having an outer diameter approximating, but smaller than, the interior diameter of said metal tube throughout at least a substantial portion of its length including said first end thereof,
• a first braze preform initially received in said first annular recess of said brazing sleeve,
• a first ceramic flux band initially formed on a first circumferential surface portion of said sleeve contiguous to said first annular recess and disposed interiorly thereof, said first ceramic flux band being formed by adhering a powder flux material on the circumferential surface portion and heating same sufficiently to melt the powder flux material to form an adherent, hard ceramic flux band,
• said brazing sleeve being positioned within said metal tube, by insertion through said open end thereof, to span said defect between said first ceramic flux band and said second end of said sleeve, said first circumferential surface portion of said sleeve being positioned beyond said defect, relative to said open end of said metal tube,
• at least said first end of said brazing sleeve being interiorly expanded and then heated to melt said first brazed preform and said first ceramic flux band and form a first sealed joint between said first circumferential portion of said sleeve and said tube, and
• said second end of said brazing sleeve including means forming a second sealed joint between said sleeve and said tube.