Method of making a pipe connection

Abstract: A pipe connection is formed in a tube plate (10) with a tube (12) of plastically deformable material which is inserted into a hole (14) in the tube plate. An annular seat (16) is provided in the wall of the hole (14). A sealing ring (18) of deformable material is placed between the seat (16) and the tube (12) in a gap formed as a result of constricting the tube (12) on its section. The tube is then expanded on its section (13) within the tube plate (10) resulting in metal to metal contact between the tube and tube plate. Expansion on the section (h1) results in the seat (16) becoming closed by an outward bent rim (20) of the tube (12), thereby compressing the sealing ring (18). The resultant pipe connection has an outer diameter (D1) on the section L1 in the hole (14) which is greater than that on the section (L) outside the hole (14).

Description: This invention relates to a method for making a pipe connection comprising a tube plane and a cube of plastically deformable material. Pipe connections consisting of a tube plate and a tube have special significance wit respect to heat exchangers widely used in heat power engineering for a heat exchange between gaseous and liquid media such as steam and water. Heat exchangers of this type consist of bundles of mutually parallel tubes which on both their ends are connected to distribution or collecting chambers. Connection is established by means of tube plates which confine the distribution or collecting chambers on their inner sides and fix the pipe bundles. The tube plates and the tubes connected thereto form pipe ccnnections. A pipe connection has to warrant suitable strength, should be corrosion resistant and leak-proof against fluids. Since the pipes of the heat exchangers occupy mutually close positions, building the pipe connection requires special technology. Technological dffficulties such as fixing by welding are aggravated by the heat exchanger pipes consisting, as a rule, of thinner material than the tube plates receiving the pipe ends. In case of materials of high strength and good weldability or suitable for soldering building of pipe connections represents a relatively simple problem. For instance, if both the tube plate and the tubes consist of steel, the tubes may be spinned in or welded into the tube place. If welding is employed, differences in the wall thicknesses of tube and tube plate require special welding technology. Where materials suitable for soldering such as steel are used, the tubes are, as a rule, fixed in the tube plates by soldering or brazing. If, on the other hand, the tubes consist of soft metal, sealing between tube plate and tube is established by means of annular gaskets made of rubber or plastics. These are placed in annular seats confined on their inner side by the tube of unchanged diameter, and closed down by a plate which means assembly work as well. In FR-A-2 185 043 a fluid-tight tube joint assembly is described wherein the pipe connection is obtained by making, in a tube plate, a circular stepped opening formed by two coaxial cylindrical wall portions of different diameters joined at an intervening radial shoulder, fixing a tube within the opening with a sealing ring positioned against the radial shoulder and expanding the tube by a mandrel so as to form two annular enlargements engaging wall portions of the opening. By the expansion the sealing ring is deformed and completely trapped in the tube plate. Another method of forming a seal between a tube and a tube plate is described in GB-A-1 551 816 in which an annular sealing element of elastomeric material is disposed between the tube and an opening in the tube plate and the sealing element is compressed by a radial expansion of the tube. The sealing element is preferably located in a groove made in the wall of the opening. In order to enhance the sealing effect there may be two or more sealing elements in axial succession. There are two or more sealing elements in axial succession also in a pipe connection described in EP-A2-0 108 958. It is the principal object of the invention to provide an improved method of making a pipe connection for heat exchangers by mechanically fixing and sealing a tube end in the opening of a tube plate. The method of making a pipe connection according to the invention is described by the features of claim 1. The sealing rings are fitted in annular grooves rolled in on the tube end opposite to annular seats in the wall of the hole whereupon the tube end will be expanded until a metal-to-metal contact between tube and tube plate is obtained and the sealing rings become compressed while the annular grooves on the tube end become straightened out. By such method positioning of the sealing rings is relatively more simple, and the more so if the inner diameter of the sealing rings is smaller than the outer diameter of the tube prior to expanding by which the sealing rings are, as it were, fixed to the tube end. The sealing rings will preferably be compressed by more than 20 percent which warrants suitable packing effect. The tube will preferably be expanded on its section beetween the inner side of the tube place and the seat by 6 to 7 per cent of the diameter of the tube which proved to be sufficient for good fixing. Closer details of the invention will be described hereinafter by taking reference to the accompanying drawings the figures of which show some exemplified steps of the method of making it and in which:- Figure 1 represents a longitudinal sectional view of an embodiment of the invention with more than one sealing ring; Figure 2 is an enlarged view of a part B of Figure 1 delimited by a circle; Figure 3 represents a pipe connection according to the invention with elliptical cross-sectional areas. Same reference characters refer to similar details throughout the figures of the drawings. In the drawings, reference character 10 designates a tube plate while reference character 12 refers to a tube to be connected to the tube plate 10 Tube plate 10 with tube 12 connected thereto represents a pipe connection 11. Tube 12 is made of soft that is plastically deformable material. E.g. aluminium or copper are such materials. The tube plate 10 may consist of steel or stainless steel. However, it may likewise be made of soft material such as aluminium. In compliance with the invention, the outer diameter D1 of tube 12 along its section L1 lying within the tube plate 10 and forming one of its ends is greater than the outer diameter D on its section below the tube plate 10. As has been mentioned, the outer diameter D1 of section L1 of tube 12 in one hole it is, preferably, by 6 to 7 per cent greater than the tube diameter D below the tube plate 10, that is D1 = (1.06 to 1.07)D. Such dimensional ratios ensure good metal-to-metal contact and, thereby, reliable fixing of tube 12 in tube plate 10. The invention can be employed also in case of tubes with other than circular cross section. E.g., the tube 12 may have elliptical shape as shown in Figure 3. In such case, in addition to favourable results similar to those previously described also a diminution of flow resistance can be obtained if the major axis T of the tube 12 is oriented so as to lie in the flow direction 24 of fluids flowing thereoutside. In Figures 1 and 2 sealing rings 18a and 18b are placed in annular grooves 12a and 12b rolled in on the end of tube 12 opposite to annular seats 16a and 16b, respectively. After expanding on section L1 compression of the sealing rings 18a and 18b as well as a metal-to-metal contact between tube plate 10 and tube 12 is obtained. In addition, grooves 12a and 12b are straightened out as can be seen on the right hand part of Figure 1. Handling of the tube 12 with the sealing rings 18a and 18b in its annular grooves 12a and 12b, respectively, is facilitated if the inner diameter of the rings 18a and 18b is smaller than the outer diameter D of tube 12 prior to expanding because, then, the sealing rings 18a and 18b become stretched when put on the end of tube 12 and snugly fit in the annular grooves 12a and 12b, respectively, of the latter. Obviously, more than two sealing rings may be provided for in a similar manner. Moreover, a number of tubes such as a pipe bundle may be fastened and sealed in the above described manner simultaneously as will be apparent to a skilled art worker. The use of two or more sealing rings has special significance where a bundle of pipes has to be built in simultaneously and a possibility of failure or a dislocation of sealing rings has to be reckoned with. As to practical values of some dimensions, the original or unexpanded tube diameter D may amount to 18.6 millimetres while diameter D1 of the hole 14 will be 19 millimetres. The axial length and the depth of the annular seats 16a and 16b may amount to 2 millimetres and to 0.5 millimetre, respectively, while sealing rings 18a and 18b will have a diameter of 1 millimetre. Expanding is preferably carried out by means of rolling mills for pipes or tubes well known in heat exchanger technology. Due to spinning in the tube end lying in the tube plate 10, section L1 of tube 12 becomes expanded. Thereby, on the one hand, tube 12 becomes mechanically fastened in tube plate 10 and, on the other hand, the sealing rings 18a,18b become flattened. As will be apparent, due to structural features and spinning in technology according to the invention the sealing rings 18a,18b in seats 16a and 16b between tube plate 10 and tube 12 are considerably deformed and put under pressure whereby very tight packing effect is obtained.

Claims: A method of making a pipe connection for heat exchangers, comprising the steps of making a hole (14) in a tube plate (10) for receiving an end of a tube (12), forming at least two annular seats (16a,16b) in the wall of hole (14), placing the end of the tube (12) into the hole (14) and providing at least two sealing rings (18a,18b) of yielding material between the hole (14) and the tube (12), and expanding the tube (12) on its section lying within the hole (14) radially until a contact is obtained between the tube (12) and the tube plate (10), whereby said at least two sealing rings (18a,18b) are compressed, characterised by providing the end of the tube (12) with annular grooves (12a,12b) corresponding to the annular seats (16a,16b) in the wall of the hole (14), fitting a sealing ring (18a,18b) into each of the annular grooves (12a,12b) and putting the end of the tube (12) into the hole (14) so that the sealing rings (18a,18b) are facing the annular seats (16a,16b), whereupon by expanding the end of the tube (12) the annular grooves (12a,12b) on the end of the tube (12) become straightened out. The method as claimed in claim 1, characterised in that the inner diameter of the sealing rings (18a,18b) is smaller than the outer diameter (D) of the tube (12) prior to expanding. The method as claimed in any of claims 1 and 2, characterised in that the sealing rings (18a,18b) are compressed by more than 20 per cent during the expansion. The method as claimed in any of claims 1, 2 and 3, characterised in that the tube (12) is expanded by 6 to 7 per cent of its diameter (D). The method according to any of claims 1 to 4, characterised in that the tube (12) and the hole (14) in the tube plate (10) have elliptical cross-sectional areas.

Inventors: BODAS JANOS, KOVACS GYULA, BODAS, JANOS, KOVACS, GYULA, Bodás, János, Kovács, Gyula
Applicants: ENERGIAGAZDALKODASI INTEZET, ENERGIAGAZDALKODASI RESZVENYTARSASAG
Application year: 1993
Main classification: F16L41
IPC codes: F16L13, F28F9, F16L41