Patent GB-1471874-A (GB)
Title: Storage tanks and methods and apparatus for manufacturing such tanks
IPC: F17C3/06
Filed: 1973-08-15
Abstract: 1471874 Making membrane tanks; welding by pressure WELDING INSTITUTE 13 Aug 1974 [15 Aug 1973] 38532/73 Headings B3A and B3R [Also in Division F4] A method of making a membrane tank includes positioning a stand 4 for a reel 5 of strip material 6 at the tank location, fixing the outer end of the strip to a traction device, e.g. a trolley 8, guiding the traction device around a track defining the tank perimeter and guiding the strip 6 by the device over a frame 1 so that the strip forms the perimeter of a section of the tank, guiding the device to pull a further length of strip from the reel and lay it alongside or overlapping the previously laid strip, moving a seaming device around the frame 1 to weld the strips together and continuing to pull further strips and to weld them to each previously laid strip until the total width of the strips is equal to the required dimension. The end of the strip 6, which is preferably of Invar (Trade Mark) but may be titanium or stainless steel, is held in the trolley 8 by jaws (13), Fig. 3 (not shown), and the trolley has an electrically driven wheel formed as a pinion for engagement with a rack on the frame 1. The trolley also has welding wheels 12, which weld the adjacent strips together when the jaws (13) are open as the trolley returns for a further strip length. The trolley 8 may be fitted with rollers (11), Figs. 2, 11 (not shown), for forming flanges on the strip edges which are subsequently welded together by rollers 12a and a support roller 12b. The rollers 12a are symmetrically displaced from the plane of the strips to facilitate their passage round the angles of the frame 1. The lap welding rollers (12), Fig. 2, form two parallel welds (21), (22), with a space (23) between them, Fig. 5 (not shown). A hole (24) is drilled through one of the strips into the space (23), so that it may be pressurized for leak testing. At the ends of the tank, the end peripheral strips are joined to end frames of thicker material, e.g. by pulsed TIG or MIG welding, and vertical strips forming the end faces are attached strip-by-strip to the end frames. The frame 1 may consist of a standard centrepiece with replaceable portions fitted around it to form the frame to the required shape. By this means a double membrane tank can be made by alternately securing outer and inner membrane strips and as the construction proceeds insulating material, e.g. balsa wood or polyurethane, is inserted between newly laid strips. The inner membrane 15, Fig. 7, is spaced from the outer membrane 18 by plywood panels 17 fixed to brackets 27, 28 which are welded to the membranes. Similarly the outer membrane 18 is fixed to a support, such as the side of a ship by plywood panels 17a. The spaces between the membranes and the ship side is filled with polyurethane foam, 19, 29. For making double membrane tanks, two vertically offset trolley tracks corresponding to the peripheries of the inner and outer membranes may be provided. The trolley may be fitted with a device for corrugating the strip and the frame may be shaped to form further corrugations extending transversely to the original corrugations. The trolley may also be arranged to move in a horizontal plane so that the strips are laid vertically above each other when making a simple cylindrical tank.