WO1998031958A2

WO1998031958A2 - Production of a metal pipe connection

Info

Publication number: WO1998031958A2
Application number: PCT/DE1997/002940
Authority: WO
Inventors: Ingo Von Hagen; Kurt Niederhoff; Markus Ring; Thomas Kremser
Original assignee: Mannesmann Ag
Priority date: 1997-01-15
Filing date: 1997-12-12
Publication date: 1998-07-23
Also published as: WO1998031958A3; DE19702719C1

Abstract

The present invention relates to a method for making a metal pipe connection (6) in the form of an intermediate tube for connecting a pipe made of a first material (7) to another pipe made of a second material (8) by means of ring-shaped welds. The intermediate tube is made of a first material at one end and of the second material at the other end, and comprises in the transition area (9) between both materials, at least in partial areas, a large surface weld. One of the two materials is used to make a first cylindrical block (1) with a conical coaxial recess (3) open to the outside, and the other material is used to make a second cylindrical block (2) having the same external diameter as the first one, the block having, outside, a conical shape at one of its two front ends. Thereafter, the two blocks are inserted into each other; then, in the area where the diameter of the conical forms is the largest, said blocks are connected to each other by a ring-shaped weld, heated at a thermoforming temperature, stretched in an extruding machine to a pin which is fully welded into the side area of the cone having a considerably smaller diameter and greater axial length, and shaped into a tubular body.

Description

"Process for producing a metallic pipe connector"

description

The invention relates to a method for producing a metallic pipe connector in the form of a pipe adapter, which is provided for connecting two pipes made of different materials. The connection should be made using circular welds. The pipe intermediate piece is formed at its ends in such a way that it consists of the material of one pipe at one end and the material of the other pipe at its other end.

One material is e.g. one austenitic steel and the other a ferritic or martensitic steel. In any case, these are materials with significantly different properties where a fusion welded connection is problematic under the operating conditions. At least in parts of the transition area between the two different materials of the

Pipe connector, these materials are welded together over a large area.

The manufacture of such pipe connectors is known from DE-PS 854 005. Two tubes made of different materials, one of which has an outer diameter that corresponds to the inner diameter of the other tube, are inserted into one another. The double-walled tube formed in this way is then compressed at one end in such a way that an increase in wall thickness results in the two material layers by enlarging the outside diameter. At the other end, the double-walled tube is compressed in the opposite way, so that an increase in wall thickness is achieved by reducing the inside diameter.

A special forming tool is required for this. In the area of the upset ends, pressure welding creates a large-area connection between the two different materials. The final shape of the pipe connector is produced by machining the two pipe ends. This is done in such a way that the end with the enlarged outer diameter is turned so far until the material of the inner layer is exposed. The other end with the reduced inner diameter is removed by drilling out the inner layer in the reverse manner until the outer material layer is exposed. In this way, a pipe connector is obtained, the two ends of which each consist of only one of the two materials.

Pipe connectors of this type, which have an austenitic material on one side and a ferritic or martensitic material on the other, can be used to connect an austenitic pipeline to a ferritic or martensitic pipeline, which can be easily welded under construction site conditions by simple circular seams. The need for such pipe connections arises particularly in the pipelines of power plants. For example, austenitic superheater pipes have to be connected to a ferritic collector.

The pipe connectors known from DE-PS 854 005 have largely proven themselves in power plant construction at the time. However, the welded connection between the different materials of the pipe connector was not always sufficiently reliable in applications with tougher conditions. To increase the axial tensile strength of the welded joint in the pipe connector, the

DE-PS 906 167 proposed to weld the large area in the transition area of the two materials by additional means such as e.g. relieve toothing, corrugation, pin locking or by additional fusion welding against mechanical stress.

Modern power plant construction aims to achieve significantly higher levels of efficiency. This is achieved through a further increase in steam temperatures. However, this involves pipeline requirements that are significantly higher than the requirements that were common in previous years. For this reason, pipe connectors of the generic type are required that are complete

Ensure welding of the two materials in the transition area with the greatest reliability. The object of the invention is therefore to propose a method for the production of such pipe connectors which manages with the usual manufacturing facilities for the implementation of the individual work steps and which ensures high reliability with sufficient economy. The present invention solves this problem in that a first cylindrical block with a coaxial, outwardly opening frustoconical recess is first produced from one of the two materials. This recess, which can be produced, for example, by machining on a lathe, extends only over part of the axial length of the block. A second cylindrical block with the same outside diameter as the first block is produced from the respective other material. At one of its two front ends, this second block is provided with a frustoconical contour on the outside. This contour of the outer truncated cone corresponds to the contour of the truncated cone-shaped recess of the first block and is therefore essentially congruent with it. The axial length of the outer truncated cone or of the hollow truncated cone should expediently be in the range from 50 to 70%, preferably approximately 60%, of the axial length of the first or second block. The tip angle of the two truncated cones is expediently set to a value in the range from 45 to 65 °, preferably in the range from 50 to 55 °. The first and the second block are plugged into each other in the area of their truncated cone shapes and then tightly connected to one another in the area of the largest diameter of the truncated cone by a circular weld seam. It may be expedient to remove the free oxygen still present between the two truncated cones in order to avoid even the slightest scaling of the bonding surface on the two truncated cones. This can be done in different ways. For example, a bore can be made at the bottom of the truncated cone-shaped recess to the otherwise closed end face of the first block. Through this hole, the

Evacuate the cavity between the two blocks. After applying the vacuum, this hole must e.g. sealed again by welding. Another possibility is to add an oxygen-binding agent, for example in a cavity that is connected to the area of the joined truncated cone surface, for example in the aforementioned bore.

Aluminum or zirconium. This cavity must then be sealed off from the outside, if necessary. The latter is of course superfluous if the oxygen-binding agent is introduced, for example, into a depression on the bottom (ie on the smaller top surface) of the inner truncated cone, if possible in the region of the truncated cone axis. After this preparation, the two are merged Blocks heated to hot forming temperature and inserted in an extrusion press. In the case of austenitic and ferritic or martensitic materials, the forming temperature is typically in the range of 1200 to 1250 ° C. In the extrusion press, the assembled block is stretched into a bolt with a significantly smaller diameter and a correspondingly greater axial length. The two materials weld completely together in the area of the conical surface. The stretching is expediently set so that the bolt produced is approximately 1.5 to 2.5 times the length, preferably twice the length, of the original axial length of the nested blocks. The pipe shape of the pipe connector is then replaced by a cutting

Further processing generated from the bolt. For this purpose, the bolt is provided with a continuous bore in the region of its longitudinal axis, the diameter of which corresponds to the inside diameter of the pipelines to be joined later with this pipe connector. The outer diameter of the pipe connector is tightened to the dimension of the outer diameter of the one to be connected

Pipelines brought. When the bolt is drilled out, any oxygen-binding agent that may be used is also completely removed from the pipe connector. Under no circumstances does it get into the bonding surface (the outer surface of the two truncated cones) during hot forming.

With regard to the contours of the outer truncated cone and the inner truncated cone, it is desirable that they overlap as completely as possible when they are plugged together. For this reason, because of the unavoidable manufacturing tolerances, the aim should rather be to set the apex angle of the truncated cone-shaped recess of the first block to be slightly smaller than the apex angle of the truncated cone of the second block than to allow an inverse dimensional deviation. A difference in the range of, for example, up to 0.5 to 1 ° is still perfectly acceptable. Furthermore, to ensure that the two frustoconical outer contours fit as closely as possible, the axial length of the frustoconical recess of the first block is selected to be slightly larger than the axial length of the truncated cone of the second block. This slight difference is expediently in the range from 0.1 to 1 mm, preferably up to about 0.5 mm. This is also a measure to control unavoidable manufacturing tolerances. This is to avoid that the length of the outer truncated cone is greater than that of the inner truncated cone. Ideally, both are the same size as the tip angles.

In an advantageous development of the invention, it is provided to produce the first block from a ferritic or martensitic material and the second block from an austenitic material. As a result, the ferritic or martensitic material lies on the outside and the austenitic on the inside in the transition area of the two materials. This has advantages with regard to the different thermal expansion behavior of these two materials. For pipe connectors that are exposed to operating temperatures of over 550 ^C C, it is recommended in the case of

Material pairings with significantly different carbon activity in the transition area of the austenitic material to the ferritic or martensitic provide a thin nickel layer in order to inhibit the undesired diffusion of carbon in this transition area. For this purpose, one of the two blocks, preferably on the

Outer surface of the second block, in the area of the truncated cone, a thin layer of nickel, for example by plasma spraying or possibly also by electroplating.

Machines and

Systems are used that are available in comparatively large numbers, as is the case for turning and drilling machines, for generating the frustoconical contours and overtightening the extruded bolt or for drilling a hole for evacuation or drilling out the bolt can be used. There are also no special requirements for the extrusion press, since it is only necessary to form a short round block with a larger diameter into a longer bolt with a smaller diameter.

The invention is explained in more detail below with reference to the figures in an exemplary embodiment. Show it:

1 two blocks with a corresponding truncated cone shape,

Fig. 2 shows a pipe connector according to the inventive method and Fig. 3 is a micrograph through an extruded bolt. In Fig. 1 two blocks 1 and 2 are shown, of which the first block 1 was made, for example, of an austenitic material. It has a truncated cone-shaped recess 3, which was produced on a lathe. The tip angle of the inner truncated cone is approximately 55 °. At the bottom of the inner truncated cone is in

A continuous bore 5 is provided in the region of the longitudinal axis. The inner truncated cone has a height d, while the remaining axial length of the block 1 has the value c. In the upper part of FIG. 1, a second block 2 corresponding to block 1 is shown, which has an outer truncated cone 4 at one end, the height of which is designated by b. The axial length of the remaining cylindrical part of the block 2 is denoted by a. The lengths a and c and b and d are usually approximately the same size, so that the heights of the two truncated cones 3 and 4 are approximately the same size. The apex angles of the two truncated cones are also approximately the same size, i.e. that the apex angle of the truncated cone 4 can be slightly larger (e.g. by up to 0.5 °) than that

Point angle of the hollow truncated cone 3. Because of the essentially congruent contours of the truncated cones 3 and 4, when the two blocks 1 and 2 are inserted into one another, the truncated cones overlap over their entire length, even if there are slight manufacturing tolerances. At least in the area of the truncated cones, the surfaces of the two blocks 1 and 2 are clean metallic. To

Putting the two blocks 1 and 2 together are tightly connected to one another by a circular weld seam. Thereafter, through the bore 5, the cavity at the bottom of the truncated cone 3 and the small space between the largely contacting conical surfaces of the truncated cones 3 and 4 is evacuated so that free oxygen is no longer available. Then the

Bore 5 tightly welded so that no more oxygen can penetrate into the existing cavity from the outside. After heating to a hot forming temperature of approximately 1250 ° C., the block assembled in this way is inserted into a hollow cylindrical die of an extrusion press and stretched into a bolt of approximately twice the length and correspondingly reduced diameter. After cooling, this bolt is turned out in the area of its longitudinal axis to the desired inside pipe dimension and then brought to the desired outside diameter by overturning. In this way, a pipe connector 6 is produced, as shown in FIG. 2. This pipe connector 6 has on one side a ferritic or martensitic part 7 and on the other side an austenitic part 8. The transition region 9 between the two halves of the material is completely welded by the pressure welding that takes place during the extrusion, without defects being ascertainable. The excellent full-surface connection between the two different materials is evident from the micrograph shown in FIG. 3 of an extruded bolt cut in the longitudinal direction.

Since the production of pipe connectors according to the invention can take place on conventional units and does not require any special tools, the investment and manufacturing costs can be kept very low. A particular advantage that results from the final cutting shape of the final shape of the pipe connector is the extraordinarily high degree of shape accuracy in terms of roundness and uniform wall thickness. Due to the high quality of the pressure welding connection between the two different materials of the pipe connector produced according to the invention, this can be easily installed in power plant construction

Use conditions in which the pressures and temperatures are significantly higher than in the past.

Claims

claims

1.Method for producing a metallic pipe connector in the form of a pipe adapter for connecting a pipe made of a first material, in particular made of a ferritic or martensitic steel with a pipe made of a second material, especially an austenitic steel, by means of welded seams, the pipe adapter being on one of it End is formed from the first and at its other end from the second material and in the transition area of the two materials of the pipe adapter, at least in some areas, a large area

Welding is present, characterized in that one of the two materials is used to produce a first cylindrical block with a coaxial, outwardly opening frustoconical recess that extends over part of the axial length of the block, and that a second cylindrical block is made from the other material Block with the same outer diameter as the first block is produced and the block is formed frustoconical on one of the two front ends, the contour of this truncated cone being substantially congruent with the frustoconical recess of the first block, that the first and the second block in the area of their Truncated cone shapes are inserted into each other as far as they will go, that both blocks in the area of the largest diameter of the truncated cone shapes are tightly connected to one another by a circular weld seam - that the two nested blocks are heated to hot forming temperature so that the two en heated blocks in an extruder to a fully welded in the region of the conical outer surface bolt with a significantly smaller diameter and greater axial length, and - that the bolt is machined into a tubular body by being in the

Provide a continuous bore in the area of its longitudinal axis, the outside is turned to size and cut to the desired axial length at its ends, its inside and outside diameters corresponding to those of the pipes to be connected.

2. The method according to claim 1, characterized in that the axial length of the frustoconical recess of the first block is chosen slightly, in particular by up to 0.1 to 1 mm larger than the axial length of the truncated cone of the second block.

3. The method according to claim 1 or 2, characterized in that any free oxygen present between the two truncated cones is removed.

4. The method according to claim 3, characterized in that a bore is attached to the otherwise closed end face of the first block at the bottom of the frustoconical recess.

5. The method according to claim 4, characterized in that the bore is sealed again after applying a vacuum, in particular by welding.

6. The method according to claim 1 or 2, characterized in that in the region of the longitudinal axis of the frustoconical recess at the bottom thereof in an indentation an oxygen-binding agent, in particular

Aluminum or zirconium.

7. The method according to any one of claims 1 to 6, characterized in that the frustoconical contours are produced by machining.

8. The method according to any one of claims 1 to 7, characterized in that before plugging into one another on at least one of the two blocks A thin layer of nickel, in particular by plasma spraying, is applied to the area of the truncated cone to inhibit carbon diffusion in the transition area of the pipe connector.

9. The method according to any one of claims 1 to 8, characterized in that the apex angle of the truncated cone shapes is set to a value in the range from 45 to 65 °, in particular in the range from 50 to 55 °.

10. The method according to any one of claims 1 to 9, characterized in that the apex angle of the frustoconical recess of the first block is set slightly, in particular by up to 0.5 to 1 °, smaller than the apex angle of the truncated cone of the second block.

11. The method according to any one of claims 1 to 10, characterized in that the axial length of the truncated cone shape in each case 50 to 70%, in particular about 60%, of the axial length of the block.

12. The method according to any one of claims 1 to 1 1, characterized in that the first block consists of a ferritic or martensitic material and the second block consists of an austenitic material.

13. The method according to any one of claims 1 to 12, characterized in that the length of the bolt during extrusion in the range of 1, 5 to 2.5 times, in particular to 2 times the original axial length of the nested blocks is set .