WO1999029976A1

WO1999029976A1 - A method for producing a pipe node for a larger and a smaller pipe in a framework

Info

Publication number: WO1999029976A1
Application number: PCT/NO1998/000361
Authority: WO
Inventors: Gunnar Foss; Per Bull HAUGSØEN
Original assignee: Marine Shuttle Operations As
Priority date: 1997-12-05
Filing date: 1998-12-04
Publication date: 1999-06-17
Also published as: GB2352015B; GB2352015A; AU1695999A; NO981338L; GB0014429D0; NO306629B1; NO981338D0

Abstract

In a pipe node for a larger and a smaller pipe (1, 2) in a framework the largest pipe (1) is provided on two opposite sides with incisions (3, 3') which penetrate the largest pipe's wall (4), together forming a through-going opening (5) through the largest pipe (1), which through-going opening (5) is larger than the smallest pipe (2). The smallest pipe (2) is passed through the through-going opening (5) and welded (7, 7') into the edges (6, 6') of the incisions (3, 3') on both sides of the largest pipe (1).

Description

A method for producing a pipe node for a larger and a smaller pipe in a framework

The invention concerns a method for producing a pipe node for a larger and a smaller pipe in a framework. The invention also concerns a pipe node for a larger and a smaller pipe in a framework.

Pipe nodes which form a connection between a larger and a smaller pipe are used to connect load-bearing pipes in frameworks. The frameworks may be level, for example constituting a base or a mast, or the frameworks may be spatial, for example constituting a trusswork which forms the jacket for an oil platform or a support structure for a bridge, or they may form a tower. The largest pipe may be one of several pipes forming vertical pillars, while the smallest pipe may form a strut.

The pipe nodes transfer forces between the pipes in the framework, and are traditionally made by welding the smallest pipe into the side of the largest pipe. The forces are thereby transferred between the pipes in a limited area on one side of the largest pipe, with the result that the material stresses in this area are relatively great, and in many cases, particularly in fatigue- stressed structures, so great that they become critical for the design of the framework. In order to distribute the forces between the pipes over a larger area, thereby reducing the material stresses, the area at the weld between the pipes can be reinforced with an external reinforcing plate. The reinforcing plate helps to reduce the material stresses, but since the forces between the pipes continue to be transferred by only one side of the largest pipe, the material stresses are still greater than desired. Moreover, reinforcing plates increase the weight of the pipe nodes, which is often undesirable.

Norwegian patent no. 158307 describes a node device for framework structures which comprises a number of nodes in which there are incorporated beamed pillars in the form of round pipes, each node containing a main pipe and one or more branch pipes. The device comprises at least one flat, rigid plate element which on at least one side is adapted for attachment of a level, cut-off end of the main pipe or at least one branch pipe and at least one transition piece with a first end which makes a smooth transition into the plate element and a second end with a cross section which is adapted for attachment of an end of either a branch pipe or the main pipe. The node according to Norwegian patent no. 158307 distributes the forces between the pipes over a larger area than the known nodes, but it has low bending rigidity across the plate element, and is also expensive to manufacture.

The object of the invention is to provide a method for producing a pipe node and a pipe node for a larger and a smaller pipe in a framework where the forces between the pipes are distributed over a larger area than in traditional pipe nodes. It is a further object that the pipe node according to the invention should have a high degree of rigidity. It is a further object that the pipe node according to the invention should be of moderate weight. The object is achieved according to the invention with a method and a pipe node of the type mentioned in the introduction, characterized by the features which are stated in the claims.

The invention therefore consists in incisions being cut out through the pipe wall on two opposite sides of the largest pipe, thus forming a through-going opening through the largest pipe, which through- going opening should be larger than the smallest pipe. The smallest pipe is passed through the through-going opening in the largest pipe and welded in along the edges of the incisions on both sides of the largest pipe. The through-going opening is preferably cylindrical and has a diameter which is only so much larger than the smallest pipe's external diameter that after being welded in, the smallest pipe has the same orientation as the through-going opening.

The forces which are transferred between the pipes are transferred via the welds along the edges of the incisions on both sides of the largest pipe, and the forces are thereby distributed over a larger area than in traditional pipe nodes. Due to the geometrical design of the sections which transfer the forces in the pipe node, the material stresses are more evenly distributed than in traditional pipe nodes. This can be demonstrated by calculations or experiments, but will also be immediately appreciated by a person skilled in the art, and this effect of the invention will therefore not be gone into in more detail.

The welds along the edges of the incisions on the two sides of the largest pipe provide two laterally secured attachments of the smallest pipe, which two laterally secured attachments have a spacing which corresponds to the diameter of the largest pipe. Due to the relatively large spacing the two laterally secured attachments have a far greater ability to absorb bending moments than the traditional attachment where the smallest pipe is only welded in on one side of the largest pipe, and consequently the pipe node has a high degree of rigidity.

The pipe node according to the invention can be reinforced with, for example, reinforcing plates in the vicinity of the welds which connect the smallest pipe to the edges of the incisions, in the same manner per se as known pipe nodes. In a preferred embodiment the reinforcements are welded into the inside of the smallest pipe, inside the welds which connect the smallest pipe to the edges of the incisions. In a further preferred embodiment the reinforcements are composed of a pipe or a sleeve which has an external diameter which is slightly smaller than the internal diameter of the smallest pipe in the pipe node, and which is placed concentrically inside the smallest pipe and welded to the inside thereof in the area of the smallest pipe which is located inside the welds which connect the smallest pipe to the largest pipe.

In a further preferred embodiment the reinforcements are composed of curved insert plates welded to the inside of the smallest pipe, and with the same curvature as the wall of the largest pipe, arranged in extension of the largest pipe's wall, with the result that the curved insert plates and the largest pipe together form a complete cylinder. A pipe node is thereby produced in which the forces are transferred between two complete cylinders which intersect each other, thus providing a particularly favourable distribution of the material stresses. The relationship between the pipe node's ability to transfer forces, its rigidity and weight depend on the specific design, but in general a pipe node according to the invention, especially the latter embodiment, has a lower weight than traditional pipe nodes which are designed to transfer equally great forces and have the same rigidity. This applies particularly to pipe nodes between thin-walled pipes.

The through-going opening may have an angle of 90° relative to the largest pipe, which, for example, may be the case if the largest pipe is one of several vertical pipes in a truss work jacket for an oil platform and the smallest pipe is a transverse stiffening. The through-going opening may also have other orientations than 90° relative to the largest pipe, which, for example, may be the case if the largest pipe is one of several vertical pipes in a trusswork jacket for an oil platform and the smallest pipe is an X-member.

In the case of the pipe node according to the invention both the largest pipe and the smallest pipe extend continuously through the pipe node, thus producing a pipe node in the form of a cross or an X. By terminating one of the pipes, or two adjacent pipes, close to the pipe node, the pipe node according to the invention can be modified into a pipe node in the form of a T or an L. If the actual joining of the pipes is according to the inventive concept, these and other modified pipe nodes produced by terminating one or more of the pipes close to the pipe node will all be covered by the invention.

The invention will have its application in a number of frameworks, and is particularly advantageous in floating, thin-walled framework structures, where low weight is of great importance. The invention will now be explained in more detail in association with a description of a specific embodiment, and with reference to the drawing, in which: fig. 1 illustrates a section of a pipe which constitutes the largest pipe in a pipe node according to the invention,

fig. 2 illustrates the pipe in fig. 1 with a through-going opening, fig. 3 illustrates a pipe node according to the invention, fig. 4 illustrates a preferred embodiment of a pipe node according to the invention, fig. 5 is a section through the pipe node in fig. 4, taken along the pipes' centre axes, fig. 6 illustrates sections of the largest pipe which was formed during the production of the through-going opening, fig. 7 illustrates a preferred embodiment of curved insert plates which form part of the pipe node, fig. 8 illustrates a second preferred embodiment of curved insert plates which form a part of the pipe node, fig. 9 illustrates a detail from figs. 7 and 8 on a larger scale, fig. 10 illustrates one of the curved insert plates in fig. 7 inside the pipe node, fig. 11 illustrates a detail from fig. 10 on a larger scale, and fig. 12 illustrates yet another preferred embodiment of the curved insert plates.

The same reference numerals are used in all the figures.

Fig. 1 illustrates a section of a pipe 1 with a centre axis 17 and an external diameter Dl . The pipe 1 will constitute the largest pipe in a pipe node for a larger and a smaller pipe in a framework. The largest pipe 1 is a thin-walled pipe and in this embodiment has internal stiffening rings 11 in order to increase the pipe's resistance to buckling and external overpressure. Such stiffening rings are prior art, and will not be discussed further. Fig. 2 illustrates the pipe in fig. 1 with a through-going opening 5 for a pipe which will constitute the smallest pipe in the pipe node. The through-going opening 5 is produced by cutting out on two opposite sides of the largest pipe 1 two incisions 3, 3' through the largest pipe's wall 4. The two incisions 3, 3' are placed in such a manner that the projection of the incisions in a plane perpendicular to the largest pipe's centre axis 17 represents coincident circles with a diameter D5, with the result that the through-going opening 5 has a cylindrical shape. The through-going opening's diameter D5 is smaller than the largest pipe's diameter Dl, but larger than the smallest pipe, thus enabling the smallest pipe to be passed through the opening. The edges 6, 6' of the incisions 3, 3' are bevelled with a view to welding in the smallest pipe. The incisions 3, 3' are further designed in such a manner that between the edges 6, 6' and the smallest pipe a gap will be formed which is so sized that together with the bevelling of the edges 6, 6' it will permit the smallest pipe 2 to be welded in in a rational and reliable manner. The bevelling of the edges and the size of the gap are selected on the basis of the prior art, and will not be discussed further. Fig. 3 illustrates a pipe node according to the invention. A section of a pipe 2 which constitutes the smallest pipe in the pipe node and has a centre axis 22 and a diameter D2 which is smaller than the through-going opening's diameter D5 is here passed through the through-going opening 5 and welded in in welds 7, 7' along the edges 6, 6' of the incisions 3, 3' on both sides of the largest pipe 1. A rigid pipe node is thereby provided where the forces between the largest and the smallest pipe are transferred on both sides of the largest pipe, as mentioned in the general part of the description.

Fig. 4 illustrates a preferred embodiment of a pipe node according to the invention. A reinforcement in the form of a curved insert plate 8 with the same curvature as the largest pipe's wall 4 is here placed inside the smallest pipe 2, in an extension of the largest pipe's wall 4, thereby filling in the area of the largest pipe 1 where the pipe wall was cut out in order to form the incision 3. This is illustrated more clearly in fig. 5, which shows a section through the pipe node in fig. 4, taken along the pipes' centre axes. To avoid making the figure over-complex, the pipes' centre axes have been omitted from fig. 5. In addition to a curved insert plate 8, fig. 5 also illustrates an opposite curved insert plate 8' which correspondingly fills in the area of the largest pipe 1 where the pipe wall was cut out in order to form the incision 3'. The curved insert plates 8, 8' are welded into the smallest pipe 2 by welds 12, 12', and it is understood from fig. 5 that the welds 12, 12' on the inside of the smallest pipe 2 are placed right inside the external welds 7, 7'. A pipe node is thereby produced which is reinforced compared to the pipe node illustrated in fig. 3, where the curved insert plates 8, 8' and the largest pipe 1 together form a complete cylinder. This gives a particularly favourable distribution of the material stresses, as mentioned in the general part of the description.

Fig. 5 also illustrates how both the largest pipe 1, the smallest pipe 2 and the curved insert plates 8, 8' are provided with internal stiffening rings 11. The stiffening rings are welded together in the welds 12, 12', thus achieving continuity in the stiffening.

Fig. 6 illustrates sections 9, 9' of the largest pipe 1 which was cut out during the cutting of the incisions 3, 3'. By adapting edges 10, 10' of the sections 9, 9', the sections 9, 9' can be used as the curved insert plates 8, 8', which gives a rational production of the curved insert plates and high material utilization. Figs. 7 and 8 illustrate preferred embodiments of the curved insert plates 8, 8'. An axis 23 which is perpendicular to the largest pipe's centre axis 17 and the smallest pipe's centre axis 22 is included in the drawing as an aid for explaining the preferred embodiments. The axis 23 thereby extends through the point of intersection of the centre axes 17 and 22. The axis 23 thereby extends right into the paper plane in figs. 7 and 8.

Here it is illustrated how sections 27, 27' of the curved insert plates 8, 8' which point towards the axis 23 are designed with end edges which meet side edges 10, 10' of the curved insert plates, forming pointed sections 31, 31' which are terminated in right or acute angles v3.

In fig. 7 the end edges are designed as rounded rectangular end edges 30, 30', while fig. 8 shows the end edges designed as curved end edges 32, 32'.

Fig. 9 illustrates one of the angles v3 in figs. 7 and 8 on a larger scale, in a cross section taken perpendicularly through the wall in the smallest pipe 2. Here it can be seen how by means of the angle v3 a pronounced termination of the weld 12 is formed between the curved insert plate 8 and the smallest pipe 2.

Fig. 10 illustrates one of the curved insert plates in fig. 7 inside the pipe node, viewed in the direction of the smallest pipe's centre axis 22, while fig. 1 1 illustrates the area in fig. 10 where the axis 23 intersects the wall in the smallest pipe 2 on a larger scale. Here it can be seen how by means of the rounded rectangular end edge 30 a design is produced where the weld 12 between the curved insert plate 8 and the smallest pipe 2 is terminated at a distance from the point of intersection between the axis 23 and the wall in the smallest pipe 2. It is thereby a practical possibility for a welder to gain access to both sides of the area where the weld 12 has to be made, which is a great advantage. Furthermore, a design is achieved where the welds 12, 12' inside the smallest pipe 2 do not touch each other, which is a great advantage with regard to the stresses in the welds. Fig. 12 illustrates the curved insert plates 8, 8' inserted in the pipe node, viewed in the direction of the axis 23. Corresponding pointed sections on the two curved insert plates 8, 8' point towards each other, i.e. the pointed section 31 on the curved insert plate 8 points towards the pointed section 31' on the curved insert plate 8' and vice versa. The termination of the end edges 30, 30' in the pointed sections 31, 31' is also preferably geometrically continuous with the wall in the smallest pipe 2, which means that the end edges 30, 30' extend over into the wall in the smallest pipe without sharp geometric transitions. In these preferred embodiments, viewed in the direction of the axis 23, the wall in the smallest pipe 2 and the end edges 30, 30' of the two curved insert plates 8, 8' form an area 34 with rounded, geometrically continuous edges. A geometric continuity is thereby produced between the curved insert plates and the smallest pipe, and material stresses in the pipe node will thereby be transmitted between the curved insert plates and the smallest pipe with far lower stress concentrations in the welds than without this geometric continuity.

In the above, the invention has been explained with reference to a specific design. It is clear, however, that variants can be implemented within the scope of the invention, in connection, for example, with the reinforcements. An example of such a variant is to provide the central areas of the curved insert plates with hatches or openings for access for welding and inspection, since this will not have particularly great significance for the material stresses in the welds between the largest and the smallest pipe and between the smallest pipe and the curved insert plates.

Claims

PATENT CLAIMS

1. A method for producing a pipe node for a larger and a smaller pipe (1, 2) in a framework, characterized by the following steps: a) to cut out incisions (3, 3') through the largest pipe's wall (4) on two opposite sides of the largest pipe (1) in order to form a through-going opening (5) through the largest pipe (1), which through-going opening (5) should be larger than the smallest pipe (2), b) to pass the smallest pipe (2) through the through-going opening (5) in the largest pipe (1), and c) to weld (7, 7') the smallest pipe (2) to the edges (6, 6') of the incisions (3, 3') on both sides of the largest pipe (1).

2. A method according to claim 1, characterized in that it further comprises welding in reinforcements in the vicinity of the welds (7, 7') which connect the smallest pipe (2) to the edges (6, 6') of the incisions.

3. A method according to claim 2, characterized in that the reinforcements are securely welded in on the inside of the smallest pipe (2), inside the welds (7, 7') connecting the smallest pipe (2) to the edges (6, 6') of the incisions.

4. A method according to claim 3, characterized in that for each incision (3, 3') it comprises welding (12, 12') in a curved insert plate (8, 8') with the same curvature as the largest pipe's wall (4) inside the smallest pipe (2) in extension of the largest pipe's wall (4), with the result that the curved insert plates (8, 8') and the largest pipe (1) together form a complete cylinder.

5. A method according to claim 4, characterized in that it further comprises producing the curved insert plates (8, 8') in such a manner that sections (9, 9') which were cut out of the largest pipe (1) in order to form the incisions (3, 3') are adapted to be welded inside the smallest pipe (2).

6. A pipe node for a larger and a smaller pipe (1, 2) in a framework, characterized in that the largest pipe (1) on two opposite sides is provided with incisions (3, 3') which penetrate the largest pipe's wall (4), together forming a through-going opening (5) through the largest pipe (1), which through-going opening (5) is larger than the smallest pipe (2), and that the smallest pipe (2) is passed through the through-going opening (5) and welded (7, 7') into the edges (6, 6') of the incisions (3, 3') on both sides of the largest pipe (1).

7. A pipe node according to claim 6, characterized in that the through-going opening (5) is cylindrical and has a diameter (D5) which is larger than the smallest pipe's external diameter (D2).

8. A pipe node according to claim 6 or 7, characterized in that it comprises welded-in reinforcements in the vicinity of the welds (7, 7') connecting the smallest pipe (2) to the edges (6, 6') of the incisions.

9. A pipe node according to claim 8, characterized in that the reinforcement is composed of a concentric pipe welded in on the inside of the smallest pipe (2).

10. A pipe node according to claim 8, characterized in that the reinforcements are composed of two curved insert plates (8, 8') with the same curvature as the largest pipe's wall (4), internally welded (12, 12') into the smallest pipe (2) in extension of the largest pipe's wall (4), with the result that the curved insert plates (8, 8') and the largest pipe (1) together form a complete cylinder.

11. A pipe node according to claim 10, characterized in that the curved insert plates (8, 8') are composed of sections (9, 9') of the largest pipe which were cut out during the formation of the incisions (3, 3').

12. A pipe node according to claim 10 or 11, characterized in that sections (27, 27') of the curved insert plates (8, 8') which point towards an axis (23) which is perpendicular to the largest and the smallest pipe's centre axes (17, 22) are designed with end edges (30, 30', 32, 32') which form approximately right or acute angles (v3) with the curved insert plates' side edges (10, 10').

13. A pipe node according to claim 12, characterized in that the curved insert plates' end edges (30, 30', 32, 32') and side edges (10, 10') meet in pointed sections (31, 31'), and that corresponding pointed sections on the two curved insert plates (8, 8') point towards each other.

14. A pipe node according to claim 13, characterized in that the termination of the end edges (30, 30', 32, 32') in the pointed sections (31 , 31') are geometrically continuous with the wall in the smallest pipe (2).