Process and apparatus for the optical checking of the shape and dimensions of the ends of tubes in a steam generator

Process for the stereophotogrammetric checking of the shape and dimensions of the ends of the tubes of a steam generator comprising a bundle of tubes (8) whose ends are fixed in a tubular plate (2) constituting a regular grid in which the positions of said tubes are accurately defined and lie flush with one face of said tubular plate (2), or primary face (2a), and a water tank (3) of hemispherical shape having at least one opening (10) in its wall, the interior space of said tank being in communication with said primary face (2a) of said tubular plate (2) and with the interior of said tubes (8), said process comprising the steps of

• (a) placing a photographic camera (15) provided with a sensitive support parallel to said tubular plate (2), inside said water tank (3), in such a manner that its optical axis remains substantially parallel to a fixed direction during the displacement;
• (b) making successive exposures of the ends of said tube lying flush with said primary face (2a) of said tubular plate (2) with said camera (15) in different determined positions, each exposure corresponding to a plurality of tubes chosen so as to obtain, by the successive exposure made, at least two views at two different perspective angles of each of said tubes (8) to be checked;
• (c) obtaining from said sensitive support extracted from said water tank (3) photographic images on a predetermined fixed scale of said primary face (2a) of said tubular plate (2) and of the ends of said tubes (8),
• (d) determining on each image the perspective angle corresponding to each said tube to be checked by measuring the space between said tubes in the neighborhood of the tubes to be checked and comparing said spacing to the corresponding spacing at the center of the image, each tube being identified in terms of its position in the regular grid of said plate;
• (e) arranging the photographic images in pairs to give a stereophotogrammetric view of the end of each of said tubes (8) to be checked;
• (f) orienting the images of each said pair with respect to each other to obtain a stereophotogrammetric image of each tube;
• (g) determining the scale of the image by measuring the spacing of said tubes on the stereophotogrammetric view and comparing said spacing with the constant spacing of said grid;
• and
• (h) observing and measuring the ends of each tube on the stereophotogrammetric view, taking the scale into account.