Westinghouse Electric Corporation

Larry M Kozak

Richard A Miller

Hermann O Lagally

Wesley G Pope

Semur P Sathi

The wall of a pressure vessel tube having cracks or other discontinuities is repaired by localized melting with the addition of an alloying material. The melting reforms or eliminates the discontinuity while the alloying material improves the physical and chemical properties of the reformed tube wall. The alloying material may be added as an insert or as a weld wire. The insert may be melted in only its center section to ensure that the entire weld is properly alloyed. Sections of the insert which are not melted may be expanded to be in intimate contact with the tube. The weld wire feed means may be integral with the welding head. A post-weld stress relief process may be applied to the welded area to reduce residual stress generated by the welding operation.

Method of repairing a discontinuity on a tube by welding

The wall of a pressure vessel tube having stress-corrosion cracks or the like is repaired by localized melting using laser welding, for fusing over defects by melting and re-solidifying the metal. A high powered laser beam is focused at a limited area or spot on the internal wall of the tube. The welding head is operated at sufficient power and is relatively moved in the tube at a sufficient rate to melt the spot while advancing along a line on the internal surface of the wall. The wall is melted to a depth of part or all of the thickness of the wall. Points at which the tube has been melted by the focused beam cool following passage of the welding head. The welding head is also advanced laterally of the line, either continuously or stepwise. Localized melting and cooling of the tube material continues progressively, line by overlapping and/or adjacent line, to melt and reform the degraded area. By successively melting, and optionally alloying linear sections of the wall using an alloying material, stress-corrosion cracks and similar defects are fused over, repairing the degraded area. The localization of the melting is such that the metal does not substantially flow and the metal cools quickly following passage of the weld head, to below a temperature of sensitization.

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Greensburg, PA, United States of America

Larry M Kozak