Patent Number: 044252960
Section: description

SPECIFIC DESCRIPTION In the drawing, the reference numeral 1 indicates a vertical steam generator traversed by water tubes 2, the ends of which are fixed to tube plates, the lower tube plate being represented by 3. At each of their ends, the tubes 2 open into chambers, the lower chamber of which is shown by the reference numeral 4. The chamber 4 is bounded by a dome 6 provided with an access aperture 7 which is normally closed in a sealed manner. A probe-holding apparatus, shown on the drawing in a general manner by the reference numeral 8, is disposed in the chamber 4. The probe-holding apparatus 8 comprises a telescopic support arm 9 biased by resilient means towards its maximum extended position and controlled by a pneumatic cylinder. One of the ends of the arm is fixed into a ball and socket joint 10, or other equivalent linkage, mounted by way of adjustable friction elements, not shown, in a cap 11 which can be fixed into the aperture 7 or can be fixed in the vicinity of the aperture. The other end of the support arm 9 is connected by a ball and socket joint 12 to a carriage 13. Two shafts 14 spaced apart from each other and on which grooved or toothed drums 15 are fixed, are rotatably mounted in the carriage 13. A belt 16, the inner face of which is grooved or toothed, passes over the two drums 15. The belt 16 carries fingers 17 or other projections which are disposed in the longitudinal central plane of the carriage and spaced apart from each other by a distance equal to the distance between two adjacent tubes 2 or to a multiple of this distance. The output shaft of a stepping motor 18 mounted on the carriage 13 is connected to one of the shafts 14, and thus enables the belt 16 to be moved. One of the ends of the carriage 16 carries a support 19 having its axis perpendicular to the plane of the carriage, and into which there is fixed a guide sheath 20, in which a Foucault current probe 21 slides together with its connection cable. The support 19 is likewise disposed in the longitudinal central plane of the carriage, and acts as guide means for the probe. A locking finger, not shown, enables the ball and socket joint 12 to be put out of action, i.e. to make the carriage 13 and the telescopic arm 9 rigid with each other in the position in which these elements lie at the moment. In order to use the probe-holding apparatus 8, the telescopic arm 9 is elongated in the direction of the tubes 2 to be examined, such that the support 13 comes into proximity with the tube plate 3, and the arm 9 is moved so as to engage the fingers 17 in the steam generator tubes 2. The probe 21 can then be inserted into a tube 2, and this tube examined. Having carried out this examination, the probe 21 is withdrawn, and the motor 18 is started while maintaining the tube 9 in its elongated position, so that the belt 16 remains in contact with the plate 3. The carriage moves over the plate, and the support 19 comes in front of a new tube 2, and this enables this latter to be inspected. This procedure can thus be carried out successively in order to check all the tubes 2 which lie in the longitudinal direction of the carriage. The tubes 2 are generally disposed along two different directions, mostly perpendicular to each other. It is therefore necessary to change the direction of movement of the carriage 13 in order to inspect all the tubes. In order to do this, after moving the locking finger for the ball and socket joint 12 into its locking position, the arm 9 is slightly retracted in order to disengage the fingers 17 from the openings of the tubes 10 in which they are engaged, and to disengage the probe-holding guide, the arm 9 remaining in its axial position by the action of the friction exerted on the ball and socket joint 10. The arm 9 is rotated about its axis through the required angle, the arm 9 is again extended so that the carriage 13 abuts against the plate 3, and the ball and socket joint 12 is released. The carriage 13 can thus be moved into contact with the plate 3, and the fingers 17 become engaged in the openings of the tubes 2 which lie along the second direction of the tube bundle. This operation is preferably carried out after previously moving the arm 9 into a position in which it is perpendicular to the tube plate 3. It is then necessary only to rotate this arm about its axis through an angle equal to that between the two tube directions, for example 90.degree. if the tubes are positioned along two perpendicular directions. It can be seen from the aforegoing description that with the aid of the apparatus, all the tubes 2 of the steam generator can easily be inspected, even those which lie at the periphery of the bundle. The apparatus can be used for any tube spacing. For this, it is necessary only to change the distance between the fingers 17 or replace the belt 16 by a belt carrying fingers which are at a suitable distance apart, and then to move the support 19 longitudinally.