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Mechanization of austenitic 18/8 Cr-Ni internal weld cladding of small diameter nozzles

The Submerged Arc Fine Wire Weld Cladding Procedure was developed for the austenitic internal cladding of 8 nozzles on the shell flange of the "Atucha 2" RPV.

In Fig. 10, arrows indicate the location  of four of this nozzles. 

The internal diameter of them was between 196 and 348 mm, at a length of up to 970 mm.

Some other welding processes had to be discarded for economic reasons (GTAW with cold wire - insufficient deposition efficiency), on geometrical grounds (manual arc - restricted space conditions), or because of increased defect frequency (GMAW).



     Fig. 10

To get this nozzles in the optimal welding position the shell flange was mounted on turning rolls as shown in Fig. 11.

The basic approach pursued when implementing the new process is illustrated in Fig. 12. The individual beads are deposited on the vertical wall. The flux is retained by means of a special device that moves as welding progresses, and which has an opening for slag extraction in its middle.

        Fig. 11  


   Fig. 12

The welding parameters and the position of the melting wire relative to the surface are matched to ensure perfect weld cladding both geometrically and metallurgically.

Fig 13 shows the design of the smallest shell flange nozzle with the internal austenitic cladding. Fig. 14 illustrate the transverse macro-section of the cladding made this way. Mostly striking is the uniformity of the weld beads and cladding layers, as well as the minor loss of thickness of the last layer after being planed by grinding.

         Fig. 13       Fig. 14 

The required δ-Fe content across the total cladding thickness can be adjusted and obtained by this process without any difficulty.

The submerged arc fine wire weld cladding technology has been successfully applied for many years and was extended to a great number of other cladding materials, as well as production and repair purposes.

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