Development of LABGENE's steam generators tube to tubesheet welding qualification procedure

The welding qualification procedure of LABGENE's Nuclear Electric Generation Laboratory - Steam Generators has special characteristics due to nuclear class 1 requirements, reduced dimensions of the LABGENE's equipment and combination of the materials involved with the tube to tubesheet welding. The welding procedure was performed using an automatic orbital welding machine without material addition. The weld joint was simulated using a sample made of a tube (ext. 12,7 BWG 18 x 90 mm) in SB-163 N08800 material and a plate (48 x 330 x 55 mm) in 20MnMoNi55 material, covered with 8 mm AWS E NiCrFe-3 cladding. For the development of the welding procedure, a lot of welding simulations were performed using machines and special devices designed for the dimensions of the pieces. Procedures related with operating, handling and cleaning conditions, essential to avoid the contamination of the pieces were issued. It was also developed a mixture of gases which contributed for the homogenising of the welding and also to avoid the appearance of cracks and defects on the weld joint. The results obtained with the performed tests fulfilled the requirements of the applied specifications and standards. The welding procedure was developed testing a lot of specimens removed from samples that were representatives of the equipment's tube to tubesheet welding. (author)