Abstract: In order to prestress a tube (4) of a heat exchanger in tension in the axial direction, with precise tailoring of the prestress, at least one of the end parts (4a, 4b) of the tube (4) is expanded diametrally using a hydraulic pressure while the tube (4) is fixed at its ends in the tube plates (3a, 3b). The value of the prestress in each of the tubes (4) of the heat exchanger is tailored by altering the initial radial clearance between the external surface of the end part (4a, 4b) of the tube (4) and the internal surface of the hole (5) passing through the tube plate (3a, 3b) in which hole the end part (4a, 4b) of the tube (4) is engaged before diametrally expanding the end part. The end part (4a, 4b) of the tube which runs substantially over the entire length of the hole (5) passing through the tube plate (3a, 3b) is hydraulically diametrally expanded.

Abstract: An end portion of each of two parts is machined and the machined end portion of the parts are arranged in facing positions to form a welding bevel extending in a longitudinal direction between the parts, whereafter a filler metal is deposited into the welding bevel. The welding bevel is a narrow bevel with side walls at an aperture angle of no more than 5° relative to the longitudinal central plane of the bevel. A nickel alloy comprising 18-32% of chromium is deposited into the welding bevel. The method is particularly suitable for joining a pressurized water nuclear reactor vessel tubing and an austenitic stainless steel primary circuit pipe.

Abstract: The machined ends of two parts (2, 4) are arranged in facing positions to form a welding bevel (6) between the parts (2, 4). A series of layers of filler metal are deposited one on top of the other in the welding bevel (6) in a direction thereof corresponding to the width of the parts (2, 4), by melting a wire (14) supplied at a predetermined feed rate to an electric arc between the parts to be welded and an electrode (13) supplied with a predetermined welding current and voltage. Each layer of filler metal essentially consists of a single weld bead across the full width of the bevel (6). The electric welding current and voltage and the feed rate of the wire (14) are predetermined in accordance with the width of the bevel (6).