CA1042944A

CA1042944A - Rolled joint system

Info

Publication number: CA1042944A
Application number: CA247,144A
Authority: CA
Inventors: Terry A. Hunter; Ernest H. Farris; Jacobus Van Winssen
Original assignee: Canadian General Electric Co Ltd
Current assignee: General Electric Canada Co
Priority date: 1976-03-04
Filing date: 1976-03-04
Publication date: 1978-11-21

Abstract

ABSTRACT OF THE DISCLOSURE

In a tubed vessel such as a calandria for a nuclear reactor the thin walls of the calandria tubes or the pressure tubes are secured to members such as end fittings by way of rolled joints wherein high axial strength and leak proof joining are achieved by rolling a surface of one member into engaging relation with a grooved mating surface of the other member, the interface between the two members being carefully sized to achieve a fit of substantially zero clearance therebetween upon assembly, so that upon rolling or otherwise swaging the joint together the residual tensile stresses in the tube member will minimal.

Description

Case 2516 ~4Z~49c This invention is directed to a tube joint, and in particular to a system for providing a high strength lea~-tight joint between a tube and a member in mutual telescoped relation.
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 develope optimum strength and leak tightness when making a joint between a tube and an associated member, such as a calandria end fitting.
One form of joint involves a rolling process 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.
It has been found that this type of joint is susceptible to crack propagation when undue residual stresses are generated in rolling the tube member. The level of residual stresses may be affected significantly by proper placement and usage of the rolling tool with which the joint is completed. A Eurther factor which can serve to minimize any adverse effects of rolling tool usage is to size the mating faces of the tube member and the end member to achieve substantially zero clearance at the initial interface therebetween, prior to rolling the joint.
In practice it has been found that whereas control of rolling conditions permit a significant reduction in residual joint stresses, the benefit in stress reduction due to providing rolled joints having substantially an initial zero clearance at their interface iB approximately one order greater.

In order to permit initial component assembly when the tube and its coupling member have substantially zero initial ~4~4~
clearance, including the condition of a slight interference fit due to oversize of the male member, or interference due to ovality of one of the two parts, a clearance between the components may be obtained by the imposition of a suitable temperatura differential, such as heating up the radially outer member in order to expand it and permit the ready insertion of the radially inner or male member, 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, resulting in minimum residual tensile stresses on the inner surface of the tube member.
It will be understood that an interference fit between the joint members may be acceptable, up to the limit where differential temperature control permits free assembly of the members prior to commencement of the rolling operation. Such an interference fit provides a degree of precompression to the inner member, 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 i~ based upon the maximum desirable temperature to which the radially outer hub member may be heated without affecting its metallurgical properties.
Owing ~o the general acceptability of interference fits in practicing the present invention, the term "substantially zero clearance" may encompass a modest interference fit and also a sli~ht clearance fit.
The present invention is of particular merit in making rolled joints with thin wall0d tubes of zirc onium niobium, which are inserted into a thick walled hub and then rolled.
As an example, satisfactory zero clearance rolled

2~4 joints in accordance with the present invention can be made in the case of zirc onium 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 tolerated.
While the present invention is of particular merit in the fabrication of fuel channel components for nuclear reactors, it is contempated 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.
Thus there is provided a method of rolling a tube member in radial joined relation with a hub member, including the steps of sizing the inner diameter of the one member and the outer diameter of the other member to substantially the same size, axially displacing one member in telescoping relation with the other member, to provide a substantially zero clearance interface therebetween, and applying a swaging force to the other member on a surface thereof remote from the one member to swage the other member in joining relation with the other member whereby a joint having a tube member with minimal residual tensile stress`is produced.
In accordance with the disclosure herein, there is provided a tube joint assembly having a radial interface between its members, an annular groove recessed in one member at the interface, the other member being radially displaced into engaging relation within the groovet the members having sub-stantially zero clearance at the radial interface whereby a condition of minimal residual tensile stress in the tube member is achieved.

~2~4~
Certain embodiments of the invention are described, reference being made to the accompanying drawing, wherein;
Figure 1 i5 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 joinedO
; 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 pairs of 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 dimension OD of the tube is substantially the same as the dimen~ion ID of the collar 12, in order to provide the "substantially zero clearance" referred to above, so that the OD may in fact slightly exceed the ID 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.

Claims

The embodiments of the invention in which an exclu-sive property or privilege is claimed are defined as follows:

1. The method of rolling a tube member in radial joined relation with a hub member, including the steps of sizing the inner diameter of one said member and the outer diameter of the other said member to substantially the same size, axially displacing into engagement one member in telescoping relation with said other member, to provide a substantially zero clearance interface therebetween, and applying a swaging force to the other said member on a surface thereof remote from said one member to swage said other member in joining relation with said other member, whereby a joint having minimal residual tensile stress in the tube member is produced.

2. The method of joint rolling as claimed in claim 1 including the step of changing the temperature of one said member relative to the other said member to produce a clearance at said interface whereby said axially telescoping step may be readily performed.

3. The method of joint rolling as claimed in claim 1 wherein said step of temperature changing involves heating said hub member so as to increase the inner diameter of a bore surface therein, said bore surface containing said annular groove.

4. The method of joint rolling as claimed in claim 1, claim 2 or claim 3, said hub member having at least one annular groove wherein material of said tube is swaged by rolling.

5. A rolled tube joint assembly having a hub member in axially telescoped relation with a tube member, having a radial interface between said members, one said member being radially swaged into engaging relation with the other said member, said members having substantially zero clearance at the radial interface whereby a condition of minimal residual tensile stress in said tube member is achieved.

6. The joint assembly as claimed in claim 5, one said member having an annular groove recessed at said interface, the other said member being swaged into sealing engagement within said groove.

7. The joint assembly as claimed in claim 6, said hub member extending about an end of said tube member and having a plurality of said annular grooves therein.

8. The joint assembly as claimed in claim 5, claim 6 or claim 7 wherein said tube is of relatively thin walled con-struction and said hub member is of relatively thick walled construction.

9. The joint assembly as claimed in claim 6 or claim 7, said hub member being of relatively thick walled construction and containing at least one said groove, said tube being of relatively thin walled construction.