Abstract: A nickel-base superalloy article which is susceptible to strain-age cracking and has a directionally oriented, single crystal, or equiaxed grain structure is repaired with minimal welding heat input into the article. The article is first heated to a welding temperature of from about 1650.degree. F. to about 2000.degree. F. in an inert atmosphere. A damaged area of the article is weld repaired using a plasma-transferred arc welder which vaporizes a filler metal in a plasma arc and deposited the vaporized metal onto the article to form a weld overlay. Minimal additional heat is added to the article during welding, as the weldment metal is vaporized remotely from the article.

Abstract: Direct electric current arc welding between an electrode and a workpiece surface is accomplished in the electric current range of about 0.5-45 amps while reversing the polarities between the electrode and the workpiece surface at a low frequency rate in the range of about 1-1000 cycles per second, in a series of polarity cycles. The workpiece surface, in at least some of the cycles, is positive for a time less than that surface is negative to result in anodic cleaning of the workpiece surface. If the arc is extinguished during a polarity reversal, the arc is maintained, for example, by restriking.

Abstract: A variable polarity device reverses the polarity of an electrically conductive workpiece and an electrode, having opposite polarities, between positive and negative in a low D.C. range of about 0.5-45 amps. Combined with the device is a control means which schedules a frequency of time rate of the reversing in the low time frequency of about 1-1000 cycles per second as well as the electric current at each polarity to provide a series of time and current defined polarity cycles for D.C. arc welding apparatus.

Abstract: A method for replacing a damaged or defective section of a length of original piping or tubing located within a structrue such as the turbine of a jet engine wherein access to the tubing is limited, and replacing such damaged section with a new section of tubing comprises inserting a cutter mounted at one end of a flexible shaft into the interior of the original tubing and rotating the shaft to cut out and remove the damaged section of tubing leaving at least one stub section of original tubing. The stub sections of original tubing are then prepared for welding or brazing to a section of replacement tubing with a series of tools each mounted to an elongated shaft. These tools include a chamfering tool, a deburring tool, and a polishing tool.