WO1986002300A1

WO1986002300A1 - A method for joining pipes in pipe-lines by means of explosion welding

Info

Publication number: WO1986002300A1
Application number: PCT/SE1984/000345
Authority: WO
Inventors: Jan DELERSJÖ
Original assignee: Delersjoe Jan
Priority date: 1984-10-18
Filing date: 1984-10-18
Publication date: 1986-04-24
Also published as: EP0197925A1

Abstract

A method for joining pipes in pipe-line systems by means of explosion welding, in which the two pipe ends to be welded together are chamfered on the outer surfaces of the pipes in a direction towards the end surfaces of respective pipes at an angle of 4o to 40o, whereafter the pipes are brought together before being welded. According to the invention, a support ring (3) is placed around the outer surfaces of the pipe ends (1, 2). The inside of the ring is provided with circumferentially extending surfaces which slope away from each other and which form an angle to the longitudinal geometric axis of the ring (3) and the pipe ends (1, 2) such that an angular difference (alpha) of 2o to 25o, preferably 4o to 15o is obtained between the chamfer of respective pipe ends and respective inclined surfaces. An explosive charge (5) is arranged around the inner periphery of the pipe ends (1, 2), and is initiated, so that the chamfered part of respective pipe ends are explosion-welded to the respective inclined surfaces of the ring (3).

Description

A method for joining pipes in pipe-lines by means of

-_*, explosion welding.

Pipes forming part of pipe-lines, particularly pipe¬ lines of large dimensions, for conducting gas or oil therethrough, are mostly joined together by means of conventional welding techniques. For safety reasons extremely high demands are placed on the mechanical strength of the weld joints, and consequently the welds must be made by highly qualified personnel and carefully inspected. Since this welding work must be carried out in open-air conditions , even bad weather conditions, it is highly cost and time consuming. At times it is also necessary to carry out the work beneath water, on the sea bottom. -

Various methods relating to explosion welding tech¬ niques have been proposed on a world-wide basis through various patents and patent applications, with the aim of achieving more positive and more economical welding methods.

The present invention also relates to the application of explosion welding techniques.

Distinct from other explosion-welded systems, a joint effected in accordance with the invention has no outwardly projecting edges or the like whatsoever on the inner surface of the pipe. The presence of such projections is liable to disturb the flow of medium transported through the pipe, or give rise to crevice corrosion at the roots of the projections. In addition, the joint configuration is so similar to that of a conventional weld joint as to enable it to be tested with conventional test equipment, suc as ultrasonic equipment or X-ray equipment, from outside or inside the pipe. The present invention relates to a method for joining pipes in pipe-line systems by means of explosion welding, in which the two pipe ends to be welded together are chamfered on the outsides of respective pipes in a direc¬ tion towards the end surface of said pipes at an angle of

O PI 4° to 40°, whereafter the pipes are brought together prior to wedding the same, the method being characterized by applying ttp the outside of said pipe ends a support ring whose inner side is provided with circumferentially extending oblique surfaces which slope outwardly from one another, these surfaces forming such an angle with the geometric longitudinal axis of the pipes and of the ring that an angular difference between the chamfer of respec¬ tive pipes and said respective inclined surfaces of 2 to 25°, preferably 4° to 15° is obtained; and by applying an explosive charge along the inner periphery of the pipe ends, and exploding said charge, whereupon the chamfered portion of respective pipe-ends is explosion-welded to said respec¬ tive inclined surfaces of said ring. The invention will now be described in more detail with reference to the accompanying drawings, in which

Figure 1a is a radial sectional view of a joint arrangement according to the invention prior to explosively welding the joint; Figure 1b illustrates the arrangement shown in Figure 1a upon completion of an explosion welding operation; and

Figure 2 is a radial sectional view of an alternative joint arrangement according to the invention prior to explosively welding the joint.

Figure 1 illustrates the principle design of the joints In Figure 1a the references 1 and 2 identify the pipe ends which are to be welded together. Each of the pipe ends is chamfered to an angle of between 4 and 40°, preferably 10° to 25°. Arranged on the outside of the pipe ends is a support ring 3, which is so formed that an angular diffe¬ rence, ex is obtained at the joint locations; α is between 2° - 25°, preferably 4° - 15°".

In order to permit the air present in the joint crevices to be expelled during the explosion-welding phase, a cavity 7 must be provided between the outer support ring 3 and the pipes 1 and 2, this cavity having at least the same volume as the air present in the joint crevices.

In the Figure 1 embodiment, the surfaces defining the cavity 7 are terminated with a support edge, the inner dia- meter of which connects with respective pipe walls. This is no way necessary to the function of the welding process and, if found suitable, can be replaced with support shoulders or inserts, or some other means of fixing the position of the support ring in relation to the pipe ends. In Figure 1a, the reference 4 identifies an insert made, for example, of rubber, plastics or metal. The insert 4 prevents smoke from penetrating down into the regions of the joint and affords protection to the inner surfaces of the pipe ends, so as to avoid undesirable cold-working hardening.

A ring of explosive charge 5 is placed around the inner surface of the insert 4 and thus radially within the pipe ends. The explosive charge is arranged to be fired by an explosive disc 6. A suitable detonator herefor is loca¬ ted in the centre of the disc 6 , thus on the centre axis of the pipes. In this way, in accordance with a preferred embodiment, the explosive charge 5 is simultaneously initia¬ ted along its peripheral symmetry line by means of the explosive disc 6, which in turn is fired by a detonator system located centrally on the disc.

According to another preferred embodiment, illustrated in Figure 2, the support ring comprises two parts, i.e. an inner ring 8 which presents the aforementioned inclined surfaces and an outer ring 9 which lies against said inner ring. The outer surface of the inner ring 8 and the inner surface of the outer ring 9 are rectilinear. In accordance with a preferred embodiment, the outer ring 9 is divided radially into segments which are held together by means of a mechanical bond, which can be released upon completion of a welding operation and the outer ring removed. The outer ring 9 may comprise two or more parts, mechanically held together by, for example, screw joints.

In an alternative embodiment, the outer ring 9 comprise

a steel strap wound several times around the inner ring 8, β. said strap being secured at its outer end by means, for example, of a weld, and can be unwound upon completion of an explosion welding operation.

OMPI

Claims

1. A method for joining together pipes forming part of a pipe-line system by means of explosion welding, in which the two pipe ends to be welded together are chamfe¬ red on the outer surfaces of respective pipes in a directio towards respective end surfaces of said pipes at an angle of 4° to 40°, and in which the pipes are brought together prior to welding the same together, characterized by arranging on the outer surfaces of the pipe ends (1,2) a support ring (3; 8,9) whose inner surface is provided with circumferentially extending surfaces which slope outwardly away from one another and which form with the longitudinal geometric axis of the ring (3; 8,9) and the pipes (1,2) an angle of such magnitude that an angular difference ( ) is obtained between the chamfer of respective-, pipe- ends and said respective inclined surfaces of 2 to 25 , preferably 4° to 15°; by applying an explosive charge (5) around the inner periphery of the pipe ends (1,2); and by exploding said charge, whereupon, the chamfered part of respective pipe ends is explosion-welded to said respec- tive inclined surfaces of said ring (3; 8,9).

2. A method according to Claim 1, characterized in that said explosive charge (5) is simultaneously initiated around its peripherical symmetry line by means of an explosive disc (6) , which is in turn initiated by an ignition system located centrally on the disc (6) .

3. A method according to Claim 1 or Claim 2, charac¬ terized in that the support ring (8,9) comprises two parts, an inner ring (8) provided with said inclined surfaces, and an outer ring (9) which lies upon the inner ring (8) .

4. A method according to Claim 3, characterized in tha said outer ring (9) is radially divided into segments and is held together by means of a mechanical bond, which can be released subsequent to the welding operation, and the outer ring (9) removed.

5. A method according to Claim 3, characterized in tha the outer ring- (9) comprises a steel band wound several

times around the inner ring (8) and secured at its outer end, preferably by welding, such that the band can be un¬ wound upon completion of a welding operation.