Abstract: A frequency-selection device, for selecting a radio-electric signal RF from a number of signals having frequencies which are situated in a given range, includes an oscillator OSC supplying a signal Vco having a variable frequency, a mixer M receiving the radio-electric signal RF and the output signal Vco from the oscillator OSC and supplying a signal FI having a frequency which is equal to the difference between the frequencies of the two signals, a frequency divider DIV supplying a signal Vco/R having a frequency which is equal to the frequency of the output signal Vco from the oscillator OSC, divided by a number R defined by a control signal CMD, a phase detector PD comparing the frequency of the output signal Vco/R from the frequency divider DIV with that of a reference signal Vref and adjusting the frequency of the output signal Vco from the oscillator OSC in the case of difference.

Abstract: The tubular casing (3) of the working head (1) exhibits two windows, upstream (4) and downstream (5), opposite each one of which there is mounted a deflecting mirror, a partially reflecting mirror (12) and a totally reflecting mirror (14) respectively. A first optical focusing device (8) is mounted in front of the upstream mirror, and a second optical focusing device (13) is mounted between the downstream mirror and the image focus (11) of the upstream optical device.Application to the simultaneous performance of a plurality of circular welds in tubes of small diameter.

Abstract: A connecting surface (24) of frusto-conical shape whose axis coincides with the axis of a pipe (23), having an apex semi-angle close to 45.degree. and a section of transverse dimension decreasing towards the end of the pipe (23) is produced on an end part of the pipe (23). A connecting surface (25) of frusto-conical shape corresponding to the shape of the connecting surface (24) of the pipe is produced on the wall member (20). The connecting surfaces (24, 25) are placed so that they coincide, and the pipe and the wall member are welded by means of an electron beam in a single pass and without filler metal, along their connecting surfaces (24, 25) from the side of the wall (20) onto which the widened part of the connecting surface (25) of the opening (22) opens. The invention applies particularly to the fastening of pipes (23) to a pipe-carrying shell (20) of a pressurized-water nuclear reactor vessel.

Abstract: A vessel comprising a shell of large thickness, for example between 200 and 300 mm, consists of unit components symmetrical in revolution (2a, 2b, 6, 7, 8, 9, 10, 3a, 3b) and connected together by end-to-end welding. The components are made of a steel containing 2 to 2.50% of chromium, 0.9 to 1.1% of molybdenum and less than 0.15% of carbon. The welding for connecting these unit components is performed by means of an electron beam in a single pass over the entire thickness of the components, without filler metal. the invention applies particularly to the manufacture of a vessel for a pressurized-water nuclear reactor.

Abstract: A process for reducing the residual stresses in a seamless metal tube which has undergone a straightening operation comprising subjecting the tube to an internal pressure of between 0.8 Pc and 1.0 Pc for a period of at least 3 minutes, while maintaining the temperature of the tube at or close to ambient temperature, Pc being the critical pressure beyond which the tube will undergo plastic deformation.