GB1583659A - Rolled joints - Google Patents

Description

(54) ROLLED JOINTS (71) We, CANADIAN GENERAL ELECTRIC COMPANY LIMITED, a Company organised under the Laws of Canada of 1420 Dupont Street, Toronto, Ontario, Canada, do hereby declare the invention for which we pray that a patent may be granted to us and the method by which it is to be performed, to be particularly described in and by the following statement: This invention is directed to a tube joint, and in particular to a method of making a high strength leak-tight joint between a tube and a member having a bore for receiving the tube.

The joining of thin walled tubes to annular members has achieved considerable significance in the nuclear reactor industry.

Due to the need for extremely high reliability it has been found necessary to develop optimum strength and leak-tightness when making a joint between a tube and an associated member, such as a calandria end fitting.

One known form of joint is made by a method involving a rolling operation wherein the radial interfaces between a tube and a surrounding bore of a member such as a fitting are joined in sealing relation by insertion and operating of a rolling tool to apply outward radial swaging force against the inner surface of the tube leading to radially outward swaging of the tube outer surface into a groove or grooves extending around an inner surface of the surrounding bore.

This type of joint, however, is susceptible to crack propagation when undue residual stresses are generated in rolling the tube member. One way in which the level of residual stresses may be reduced significantly is by careful control of the placement and usage of the rolling tool with which the joint is completed. This, on its own, however, does not produce the best possible joint from the point of view of leak-tightness and durability due to a low level of residual stresses. It has been found, by employing the joint forming method of the present invention defined below, that whereas control of rolling conditions permit a significant reduction in residual joint stresses, the benefit in stress reduction due to the use of the method of the present invention is approximately one order greater.

According to the present invention, there is provided a method of making a joint between a tube and a member having a bore for receiving the tube, comprising the steps of working the tube and/or the hole in the member to bring the surfaces which in the completed joint are to be in contact with one another into a substantially zero clearance (as herein defined) relation, positioning the tube within the bore to provide a substantially zero clearance (as herein defined) interface therebetween, and rolling the interior of the tube to complete the joint.

The term "zero clearance" when used herein will be understood to refer to the relative dimensions of two fitting components having correspondingly shaped cooperating surfaces the dimensions of which are nominally the same, with a manufacturing tolerance permitting a very small diametral clearance, up to a maximum of 0.002" or a small interference sufficient to permit free assembly to be obtained by causing a temperature difference in the two parts, for example, up to about 0.007" diametral interference. It will be appreciated, therefore, that on average there may be a very slight interference between the tube and the bore which will prevent them from being simply fitted one inside the other. For facilitating this step in the method of the present invention and to permit initial component assembly, it is preferred that the method includes the step of changing the temperature of the tube or the said member relative to the other to produce a clearance at the said interface to permit insertion of the tube into the bore.

The temperature changing step may be effected, for example, by heating up the said member in order to expand it and permit the ready insertion of the tube into the bore.

After permitting the two components to cool to the same temperature, and hence return to the zero clearance condition, the joint may then be rolled: it has been found that this results in a joint having minimum residual tensile stresses on the inner surface of the tube. Such an interference fit provides a degeee of pre-compression on the tube, which precompression is acceptable, provided it does not result in unacceptably high residual stresses on the outside surface of the inner or tube member.

One limit of such precompression is based upon the maximum desirable temperature to which the member having the tubereceiving bore may be heated without affecting the metallurgical properties.

The present invention is of particular merit in making rolled joints with thin walled tubes of zirconium niobium, which are inserted into a thick walled hub and then rolled.

As an example, satisfactory zero clearance rolled joints in accordance with the present invention can be made in the case of zirconium niobium tubes of a nominal four inch diameter having a wall thickness of 0.165 inches, wherein a clearance ranging from a .002" diametral clearance to a 0.007 inch diametral interference can be successfully assembled and rolled so as to give residual tensile stress of a value which may be folerated.

While the present invention is of particular merit in the fabrication of fuel channel components for nuclear reactors, it is contemplated that it may well be of importance in making rolled joints for other applications involving crack sensitive materials e.g.

boilers, heat exchangers and condensers. As such the hub member may or may not have annular grooves.

The present invention also comprehends a tube joint assembly made by the method of the invention as defined herein.

Certain embodiments of the invention are described, reference being made to the accompanying drawing, wherein.

Figure 1 is a diametrical cross-section of a joint in accordance with the teachings herein disclosed, and Figure 2 is a view at 2-2 of Figure 1.

Referring to the drawings the assembly 10 comprises an annular collar 12 having an internal bore 14 within which a tube 16 is inserted and joined.

The rolled joint is shown to comprise three annular grooves 18 extending about the bore 14, into which the material of the tube 16 is displaced by means of rolling.

The rolling is effected by way of three pairs of axially aligned rolls 22, each comprising a long roll and a short roll in staggered relation so as to avoid the generation of a squeeze line about the inner surface of the tube 16.

The outer diameter of the tube is nominally the same as the inner diameter of the collar 12, in order to provide the "substantially zero clearance" referred to above, so that the outer diameter may in fact slightly exceed the inner diameter in value. Rolling of the joint so as to fill the grooves 18 involves the use of rolls 22 and a tapered mandrel 23, as is well known in the art.

WHAT WE CLAIM IS: 1. A method of making a joint between a tube and a member having a bore for receiving the tube, comprising the steps of working the tube and/or the hole in the member to bring the surfaces which in the completed joint are to be in contact with one another into a substantially zero clearance (as herein defined) relation, positioning the tube within the bore to provide a substantially zero clearance (as herein defined) interface therebetween, and rolling the interior of the tube to complete the joint.

2. A method of making a joint, as claimed in Claim 1, including the step of changing the temperature of the tube or the said member relative to the other to produce a clearance at the said interface to permit insertion of the tube into the bore.

3. A method of making a joint, as claimed in Claim 2, wherein the step of temperature changing involves heating the said member to increase the inner diameter of the said tube-receiving bore therein.

4. A method of making a joint, as claimed in any preceding claim, including the step of forming at least one annular groove in the inner surface of the tubereceiving bore which contacts the tube in the completed joint, into which groove material of the tube is swaged by the rolling.

5. A method of making a joint, as claimed in Claim 4, including the step of forming a plurality of annular grooves in the said inner surface of the tube-receiving bore.

6. A rolled tube joint assembly when made by a method as claimed in any

Claims (1)

1. preceding claim.

   7. A joint assembly as claimed in Claim 6, in which the said member extends about an end of the said tube.

   8. A joint assembly as claimed in Claim 6 or Claim 7 wherein said tube is of relatively thin walled construction and the said member is of relatively thick walled construction.

   9. A joint assembly as claimed in Claim 6 or Claim 7, in which the said member is of relatively thick walled construction and the bore therein contains at least one annular groove, the said tube being of relatively thin walled construction.

   10. A method of making a joint between a tube and a member having a bore therein for receiving the tube, substantially as herein described with reference to the accompanying drawings.

   11. A rolled tube joint assembly substantially as herein described with reference to and as shown in the accompanying drawings.