The present invention relates in general to casings for accessories, such as steel casings for gate valves, and a method and apparatus for making the same and, in particular, to a new and useful casing particularly for gate valves which have a relatively large or very large nominal width which are usable in installations requiring high and very high safety measures, such as thos required in the manufacture or construction of a nuclear reactor, and to a method and apparatus for making the same.
Gate valve casings used in the construction of nuclear reactors, which have large to very large nominal widths, such as from 300 mm to 600 mm, have been manufactured by working, e.g., by milling, the entire casing out of a steel bloom, for example, and this construction entails very high costs.
Gate valve casings of such large nominal widths and for satisfying safety conditions have also been made by longitudinally welding two casing parts together.
The valve seat rings cooperating with the shutoff member, thus with the gate, are also welded to the casing, in the interior thereof. Also welded to the casing are pipe connections for connecting to the piping proper. A flange is eventually welded to the top of the casing, to which a collar may be secured by screws. However, there are also known constructions where such covers are fitted in grooves so that no welded flanges are needed.
With gate valves used under increased safety conditions, such as in nuclear plants, the welding seams must meet the highest requirements of quality. This involves the necessity of providing for the possibility of radiographic and also ultrasonic inspection. Such a possibility, however, is not provided for in the prior art constructions since, for example, in the last-mentioned construction, the location of the welded seams does not permit X-ray and ultrasonic tests. More particularly, sufficient distance of approach is not available for the test head of such ultrasonic test instruments, and it is equally difficult to take radiographs with the prior construction.
Since, in conventional gate valve casings having such large nominal widths, six or even more welding seams are frequently provided between the fairly large number of individual parts welded together, such a construction cannot properly be used under the required safety conditions.
Numerous other casings for accessories, particularly for gate valves, are known, however, which cannot be employed in safety zones, such as nuclear plants, since they are small in size and, in addition, have welded seams which are inaccessible for radiographic and ultrasonic inspection. Additionally, many of these constructions are rather expensive since they are made of a plurality of individual parts which must undergo relatively highgrade machining and are unsuitable for larger or very large casings, for example, of a nominal width of 300 mm to 1,000 mm.
The following references are cited as of interest to the present invention:
"Advanced Technology of Fittings particularly With Regard to the Quality Control" by W. Kranert, "3R International", Vol. 15, No. 9, September, 1976, pages 530 to 535;
"Manual of Welding" by Paul Schimpke and Hans A. Horn, Third Edition, publishers Springer-Berlin 1943, pages 173/180;
"Welding of Iron Materials" by Ludwig Zeyen and Wilhel Lohmann, Second Edition, 1948, publishers, Stahleisen mbH, Dusseldorf, page 297;
German Pat. Nos. 755,989; 973,519; 1,928,585 and 1,000,652;
German Auslegungschrift Nos. 2,032,132; 1,425,710; 2,164,929 and 2,354,246;
Published Patent Application No. S 28 115 XII/47 g;
Class 47 g, Groups 39 01;
German Offenlegungschrift Nos. 2,057,746; 1,928,686; 2,114,068 and 2,041,333; and
German Utility Model No. 7,031,192.