GB2203684A

GB2203684A - Joint on steel pipes

Info

Publication number: GB2203684A
Application number: GB08808074A
Authority: GB
Inventors: Heiner Bogdahn; Bernd-Peter Salzberg; Manfred Feinmechanik Langhanki
Original assignee: TELTOV GERAETE REGLER
Current assignee: TELTOV GERAETE REGLER
Priority date: 1987-04-09
Filing date: 1988-04-07
Publication date: 1988-10-26
Anticipated expiration: 2008-04-07
Also published as: DD259662A1; GB8808074D0; DE3809479A1; GB2203684B; HUT53954A

Description

2 2 0, M114 TITLE: Joint on steel pipes.

The invention relates to the construction of a joint for connecting pipes of small diameter of unalloyed, low alloyed and/or high-alloyed steel. This joint construct ion comes into use especially in installations which are demanding as regards safety, as for example nuclear power works or installations requiring Execution Classes 1A or IB.

Pipelines in installations which must satisfy high quality demands in their execution (for example in the first and second cycles of nuclear power plant or in chemical installations, which conform with Execution Class IA or IB) are as a rule joined by a "WIG" welding process.

Since the quality of the weld seams is very greatly dependent upon the skills of the welders, the joints are always inspected by an irradiation test (X-ray). The procedure of weld seam testing is very expensive, since V about ten times as much time is needed for the testing as for the production of the weld seam. This disproportion determined the development of a diffusion welding process for building site use (F. Salzberg, H. Bogdahn:

"Production of welded/soldered connections under argon 99.0.9 with resistance heating" "Sch,,.,eisstechnik", Berlin (1985), Vol. 61 pp. 240, -.251). With this process, 2 since it is a partially automated welding processs it is possible to produce connection qualities which are most extensively independent of the skills of the welder.

Since these co-i.nections cannot be tested by X-ray, the quality of the welds is tested on a parallel sample subjected to bending stress. An achieved bending angle of 1000 is a sure sign that the parameters necessary for welding are correctly set. The quality assurance by reference to a parallel sample is adequate for installat ions in the conventional range.

This productive welding process cannot be used for the setting up of installations in nuclear power plant, because on account of the absence of any possibility of destruction-free testing of every joint, any reductions of quality cannot be detected and thus a certain residual risk remains.

It is the aim of the invention to produce a joint in pipes of steel which is distinguished by high reliability but at the same time is simple in production.

It is the problem of the invention to produce a joint in steel pipes, the strength of which at least corresponds to that of the basic material and which is so secure that no more residu'al risk occurs, so that it is possible to dispense with X-ray testing.

In accordance with the invention this problem is solved in that the pipe connection, produbed in one heating operation, consists of a diffusion-welded 3 connection and a combined diffusion-welded/soldered connection, where the diffusion-welded connection and the combined diffusion-welded/soldered connection do not lie in one plane.

In an advantageous development of the solution in accordance with the invention the diffusion-welded connection produced between the pipe end faces is jacketed by a combined diffusion-welded/soldered connection produced by means of a sleeve. This combined diffusion welded/soldered connection jacketing the diffusion-welded connection can also be forted by a T-piece.

Next the functional features of this joint construction in accordance with the invention are to be described briefly. Let it be set forth as most essential aspect that both connections, that is the diffusion-welded connection between the pipe end faces and the combined diffusion-welded /soldered connectiorh lying outside this plane between Dipe and sleeve, are produced at the same time, that is in one heating operation, in order to preclude damage to the basic material. This is realised by a diffusion-welding process known per Re, working on the basis of electric resistance heating under protective gas.' In addition however a sliding sleeve is fitted over the Dipe interfwe. Then the current heat not only diffusion-welds the pipe ends but also melts the solder rings deposited on the sleeve ends. By capillary action the liquid additional material passes into the gap between sleeve and pipe. Surprisingly however it is not a pure soldered connection but a combined diffusion-welded/ soldered connection which occurs in this gap.

4 Each joint individually possesses the strength of the basic material, so that there is double security from the outset against failure of the pipe connection. if nevertheless a joint connection should fail, the remaining connection is still in a position to transmit the occurring forces without failure.

As additional material a material is to be selected the liquidus temperature of which lies in the r--r-jrange of the basic material to be joined, so that good condit ions are also i=esent in a short time for the diffusion welding of the pipe end faces.

The invention is next to be explained in greater detail by reference to an example of embodiment.

FIGURE 1 shows the assembly according to the invent- ion of a joint on steel pipes, by means of a sliding sleeve and FIGURE 2 shows the assembly according to the invent- ion by means of a T-piece.

Pipes of high-alloyed steel X8CrIliTi 18.10 of dimensions 12 x 2 are to be joined with one another. For this purpose an apparatus for the diffusion-welding of pipes which is known per se but somewhat modified is used (P. Salzberg, H. Bogdahn "Production of welded/soldered connections under argon 99.99 with resistance heating", "Schijeisstechnik,, Berlin 35 (1985) vol. 6, pp. 249 -251).

The end faces 2 of the pipes 1 are machined with an end-milling cutter so that plane-parallel faces standing perpendicularly of the pipe axis are produced. After the the cleaning of the entire joint area with a grease solvent, solder rings of a heat-conductive alloy, which consists essentially of 30 % Nil 20 % Cr and remainder iron, are oriented at the joint by means of a gauge. The sliding sleeve 3 is fitted between the solder rings.

Then the pipe ends thus prepared are clamped into the already-mentioned diffusion-welding apparatus. The modification of the known apparatus becomes necessary because heat is withdrawn from the joint by the arrange ment of the sleeve around the pipe interface, while the pipe has already reached the solidus temperature. For this reason the distance between the collar carriers must be adapted to these modified conditions, since too great an interval leads to overheating of the basic material.

After the pipe ends have been clamped in this modified apparatus, the protective gas chamber is closed, scavenged with argon and,the heating process is initiated.

When the solder rings positioned on the sleeve edges are molten, the heating is terminated.

The connections thus produced possess double security compared with the known welded seam or soldered seam constructions. A diffusion-welded connection has been produced between the end faces 2 of the pipes 1 at the pipe interface by the action of temperature, time and pressure (elastic deflection of the collar ca-riers). In addition to this connection a combined diffusion-welded/ soldered connection is produced between external diameter 4 of the pipe ends and the inner circumferential surface of the sliding sleeve 3 jacketing the pipe interface.

6 This combined diffusion-welded/soldered connection is likewise alysult of the elastic deflection of the collar carriers in co-operation with pressure and temperature.

This has the effect that pressure faces for the pipes to be joined occur in the sliding sleeve, in the region ofWych then the formation of a diffusion-welded connection occurs. In the remaining gap region a soldered connection develops. Each connection individually. both the diffusion-welded connection and the combined diffusion welded/soldered connection, possesses the strength of the basic material. Thus such high security of the joint is achieved that a residual risk is excluded and thus it is possible to dispense with a destruction-free testing.

The same joint construction is also achievable when using T-pieces 7 (Figure 2). Here in principle three joints occur, and each joint again consists of a diffusion-welded connectio'n at the pipe interface 5 and a combined diffusion welded/soldered connection on the circumferential surfaces of the pipe ends 6. It is merely necessary to use an apparatus which permits of joining in the 90 0 direction.

7

Claims

Claims

I.) Joint on steel pipes, characterised in that the pipe connection produced in one heating operation consists of a diffusion-welded connection and a combined diffusion- welded/solldered connections wherein the diffusion-welded c6nnection and the combined diffusion-welded/soldered connection do not lie in one plane.
2.) Joint on steel pipes according to Claim 19 characterised in that the diffusion-welded connection produced between the pipe end faces (2) is jacketed by a combined diffusion-welded/soldered connection produced by means of a sleeve (3).
3.) Joint on steel pipes according to Claim 1, characterised in that the diffusion-welded connection is formed on the pipe interface (5) and the combined diffusion-welded soldered connection jacketing this pipe interface (5) is formed by a T-piece (7)
4.) Joint on steel pipes substantially as described with reference to Figure 1 or Figure 2 of the accompanying drawings.

PubUbhed 1988 at The Patent Office, State House, 86171 High Holborn, London WC1R 4TP. Further copies may be obtained from The Patent Office, Sales Branch, St Mary Cray, Orpington, Kent BR5 3RD. Printed by Multiplex techniques ltd, St Mary Cray, Kent. Con. 1187.