WO1998025712A1

WO1998025712A1 - Process for producing internally plated pipes

Info

Publication number: WO1998025712A1
Application number: PCT/DE1997/002944
Authority: WO
Inventors: Manfred Keller; Ingo Von Hagen; Rolf Kümmerling; Wilfried Schmidt; Theodor Schmitz
Original assignee: Mannesmann Ag
Priority date: 1996-12-13
Filing date: 1997-12-12
Publication date: 1998-06-18
Also published as: NO992565D0; EP0944443A1; DE59703252D1; EP0944443B1; AU5651398A; NO311967B1; NO992565L

Abstract

This invention concerns a process for producing internally plated pipes which, as compound pipes with an outer diameter of at least 60 mm, are used for transport of corrosive and/or abrasive fluids. To that effect, a second (inner) pipe (2) with a slightly smaller outside diameter than the inner diameter of an outer pipe (1) and a wall thickness of at least 1 mm is inserted into an outer pipe (1) of carbon steel or another more resistant metallic material. The inner pipe (2) is made out of another material, particularly of a corrosion resistant and/or wear resistant metal. Moreover, the outside pipe is reduced in diameter by forced fit using a reducing ring (4) so that the outer pipe (1) is mechanically reduced to press against the inner pipe (2). This invention is characterized in that the reduction of the diameter of the outer pipe (1) using a reducing ring (4) is only carried out to the extent that the mechanical deformation of the inner pipe, which is brought about by the pressing on of the outer pipe onto the inner pipe (2), still remains within the elastic range.

Description

Process for the production of internally clad pipes

description

The invention relates to a method for producing internally clad pipes, which are provided as composite pipes with an outside diameter of at least 60 mm for the transport of corrosive and / or abrasive fluids (gases, liquids, suspensions). A second (inner) tube with an outer diameter that is slightly smaller than the inner diameter of the outer tube and a wall thickness of at least 1 mm is inserted into an outer, usually thick-walled tube made of carbon steel or another high-strength metallic material. The inner tube consists of a different, in particular a corrosion-resistant and / or wear-resistant, metallic material and generally has a thinner wall thickness than the outer tube. Between the inner and the outer tube, a non-positive connection is created in the sense of a press fit by mechanical shrinking, by reducing the diameter of the outer tube by forcing this tube through a reducing ring.

Clad pipes are composite components in which technical and / or economic advantages are achieved by combining two different materials depending on their intended use. Mostly you want the good corrosion-chemical properties of high-alloy steels with the superior mechanical properties of z. B. connect carbon steels. But the combination of particularly wear-resistant materials with conventional structural and stainless steels can also bring technical and economic advantages. The

Economic efficiency follows from the fact that the layer thicknesses of the mostly very expensive plating materials can be reduced to the level that is technically necessary for the respective application. With the increasing exhaustion of the easily accessible deposits of hydrocarbons, the use of so-called acidic products has increased significantly, particularly in the offshore industry. These products are oil, gas or condensate with proportions of C0 ₂ , H ₂ S and chlorides. The promotion of such products is associated with considerable corrosion problems. This can be partially prevented by injecting chemical inhibitors. However, it is often necessary to use delivery lines and transport lines made of correspondingly corrosion-resistant alloys. Austenitic-ferritic duplex steels are often used here. With increasing depth of conveyance, the temperatures of the products to be conveyed also increase, which means that

Corrosion problems are significantly exacerbated.

With higher H ₂ S contents and additional CO ₂ and chloride contents, the risk of stress corrosion cracking increases. If the use of duplex steels is no longer sufficient, highly corrosion-resistant materials such as B. high-alloy austenitic steels and in extreme cases even nickel-based alloys can be used. Due to the low yield strengths in the annealed condition of these materials and their high prices, the use of solid wall pipes made from these materials is often not only technical but also economic. In such cases, e.g. B. carbon steel tubes with corresponding

Inner claddings made of high-alloy materials can be an interesting alternative. This applies both to small-format seamless pipes (for tubings and flowlines) and to large-format longitudinally welded pipes (for pipelines).

Another area of application is hydraulic solids transport through pipelines. In particular, abrasion wear and, if necessary, additional corrosion wear occur. Composite pipes equipped with appropriate wear-resistant inner claddings are therefore often used for such tasks. The plating is often applied by welding plating. This process is very complex.

The composite pipes considered here are basically pipes whose wall consists of two layers of different material compositions. A distinction is made between pipes with a metallurgical bond of the layers from those with a purely mechanical bond (so-called soundproof Links). Composite pipes of the first type can be produced using the known methods of coextrusion, roll cladding, hot isostatic pressing, explosive cladding or also welding cladding. A disadvantage of composite pipes, which are produced by hot forming, can be seen in many cases in that after the forming, the usage properties of the base and support material are not in an optimal condition. For setting z. B. the required mechanical properties of the carrier material consisting of a carbon steel and the corrosion-chemical properties of the plating material consisting of a high-alloy material, an additional heat treatment is therefore often required. This provides one for the carrier material

Tempering treatment and solution annealing treatment for the plating material. Inevitably, both treatments have to be carried out simultaneously and therefore cannot be carried out optimally for each layer, rather a compromise in the temperature control must be found.

Various methods are known for producing composite pipes with a mechanical bond. There are two different ways to do this. In both cases, an inner tube with a generally higher quality material is assumed, which is inserted into an outer tube with a generally greater wall thickness made of low quality material. The

The outer diameter of the inner tube is close to the inner diameter of the outer tube. In the first production route, the inner tube is expanded against the outer tube in order to produce the mechanical bond. This can be done, for example, by means of a hydraulic expanding and stamping press, as is known from the company brochure "PRODUCT - BUTTING BIMETAL PIPES". With this

Processes can also produce composite pipes with larger diameters.

In a second method, the mechanical connection between the inner and the outer tube is produced by forcing an increase in the diameter of both tubes by pulling them together through a drawing ring. This can be done without the simultaneous use of an internal tool, as is known from US 4125924. However, a plug arranged in the deformation area of the drawing ring can also be used as an internal tool, as is known from US Pat. No. 3,86,338. In this document, a method is also described as a further method of production, at Similar to the use of a hydraulic expansion press, the inner tube is expanded against the outer tube with the help of a pulling plug.

It is common to all these processes that both the inner and the outer tube of a plastic one are used in the production of the mechanical bond

Is subjected to deformation.

A method is known from Japan in which the mechanical bond between the inner and outer tube is produced by expanding an outer carbon steel tube by thermal expansion and hydraulically expanding the thin-walled tube lying in it from the plating material. After the outer tube has cooled down, the outer tube is shrink-fitted to give an interference fit between the inner and outer tubes.

The advantages of composite pipes with a purely mechanical connection between the inner and outer pipe are, in particular, the significantly lower production costs compared to composite pipes with a metallurgical bond. One disadvantage is the limited further processability, for example in hot forming into pipe bends. In addition, care must be taken to ensure that no moisture penetrates into the contact zone between the inner and outer tube, which could lead to corrosion. The latter, however, only plays a role before laying such a composite pipe.

In the known methods for producing mechanically connected composite pipes, the plastic deformation of an inner high-alloy pipe has a major disadvantage. This consists in that the corrosion resistance is adversely affected by the plastic deformation. This is particularly important in terms of resistance to stress corrosion cracking.

The object of the invention is to propose a generic manufacturing method for mechanically bound composite pipes, in which the corrosion resistance of the inner pipe reaches the highest possible level, particularly with regard to stress corrosion cracking. This object is achieved according to the invention in a generic method in that when a reducing ring is forcedly passed through which the outer tube with the inner tube therein is conveyed, the reduction in the diameter of the outer tube is only driven to the extent that the Shrinking the outer tube onto the inner tube causes mechanical deformation of the inner tube still remains in the elastic range. The forces acting on the inner tube from the outer tube are thus limited during the deformation so that the inner tube is not subjected to any plastic deformation. This means that its good corrosion-chemical properties are retained in full.

For larger pipe diameters, it is expedient to pass the reducing ring by pushing the outer pipe through the reducing ring in the direction of the pipe axis. This is preferably done on an Erhardt drawing press. In particular with smaller pipe diameters, the reducing ring can also be passed by pulling in a manner known per se.

In order to keep the forces acting on the inner tube during the deformation of the inner tube within the permissible limits, the geometrical influencing variables relevant for the deformation must be coordinated with one another in a corresponding manner. This applies in particular to the following sizes:

Inner diameter of the reducing ring at the outlet outer diameter of the outer tube used - wall thickness or inner diameter of the outer tube used outer diameter of the inner tube used.

When reducing the outer tube, the deformation must be adjusted so that the new inner diameter of the outer tube corresponds to the outer diameter of the inner tube, taking into account a sufficient preload (press connection between inner and outer tube). The originally existing air gap between the inner and the outer tube must therefore be completely closed. For the inner and outer tubes, in particular seamless or longitudinally welded tubes can be used. Metallic tubes with a helical weld are less preferred. In addition to conventional carbon steels, martensitic chrome steels, duplex steels or, in special cases, austenitic or ferritic steels are also used as materials for the outer tube

Stainless steel in question. In comparison, the materials for the inner tube are generally of higher quality; martensitic chrome steels, duplex steels, austenitic stainless steels, titanium or titanium alloys and finally also nickel-based alloys are particularly suitable. In special cases, the inner tube can also be formed from a high-temperature alloy. The outer tube preferably has a wall thickness which is clearly above the wall thickness of the inner tube. In an expedient embodiment of the invention, the wall thickness of the outer tube is at least 3 mm and its outer diameter is at least 110 mm. The wall thickness of the inner tube should not be more than 6 mm, particularly in the case of large-size tubes, particularly for cost reasons. In order to protect the outer tube against corrosion, in particular if it is made of carbon steel, it is preferred to provide the composite tube with an anti-corrosion coating on the outside. A particularly expedient version of the corrosion protection provides for a three-layer insulation with an epoxy resin base layer, an ethylene copolymer adhesive layer and a final polyethylene cover layer. However, epoxy resin thick-layer insulation or bitumen coatings can also be applied, for example. The composite tubes produced according to the invention are expediently mechanically processed on their end faces and then welded gas-tight in the annular area of the connection point between the outer and inner tube, so that no moisture can penetrate into the bonding area between the inner and outer tube during storage or during transport.

The invention is explained in more detail below with the aid of the single figure, which shows a composite pipe in the deformation area of a drawing ring in the form of a sectional view. An inner tube 2, whose outer diameter is somewhat smaller than the inner diameter of the outer tube, is telescopically inserted into an outer tube 1. The inner surface of the outer tube and the outer surface of the inner tube are metallically clean and were possibly pushed before one another cleaned accordingly. This loose unit made of outer tube 1 and inner tube 2 is then pushed through a stationary reducing ring 4 with the aid of a hydraulically driven punch 3, for example, which expediently has a holding mandrel for coaxially centering the inner tube 2. The reducing ring 4 reduces both the outer and the inner diameter of the outer tube 1 in such a way that the originally existing air gap between the inner tube 2 and the outer tube 1 is completely closed. In addition, the inner diameter of the outer tube is reduced to such an extent that there is a pretension with respect to the outer surface of the inner tube 2, this pretension, however, being so limited that the deformation of the inner

Tube 2 remains in the elastic range. The plastic deformation taking place in the method according to the invention is therefore limited exclusively to the outer tube 1. Due to the resulting interference fit between the outer tube 1 and the inner tube 2, a so-called soundproof bond is formed.

The main advantage of the method according to the invention compared to the known methods described, which use a hydraulic expansion of the inner tube to achieve the mechanical bond, lies in the considerably simpler process control and in the fact that the inner tube does not undergo any plastic deformation. In this way, the previously e.g. by a

Solution annealing set optimal corrosion-chemical properties of the inner tube even on the finished composite tube completely. In addition, the method according to the invention is suitable for the production of composite pipes in a very wide range of dimensions. In particular, large-format pipes with outer diameters up to 660 mm and wall thicknesses of the outer pipe up to 35 mm can be produced without any problems. Existing production facilities, such as an Erhardt drawing press, can be used without major investment, especially since standard tools can be used to reduce the diameter.

Another advantage of the method according to the invention lies in the fact that the plastic deformation behavior of the inner tube material plays no role here. This allows a very large number of tube material combinations. In contrast, in processes in which the mechanical bond is achieved by internal expansion, the plastic deformation properties of the involved pipe materials to be coordinated. For example, the remaining plastic deformation of the outer tube must be smaller than that of the inner tube in order to produce a gap-free bond. If the elastic modulus of the two composite materials is approximately the same, the yield strengths and / or the further course of the hardening curves (stress-strain

Curves). For example, with approximately equal yield strengths of the outer and inner raw materials, the hardening curve for the latter is flatter than that for the outer tube material in order to produce a firm press fit. This requirement restricts the selection of suitable pipe materials for processes that bring about the mechanical connection by plastic deformation of both pipes. This is not the case with the present invention.

Claims

claims

1. Process for the production of internally clad pipes, which are provided as composite pipes with an outer diameter of at least 60 mm for the transport of corrosive and / or abrasive fluids, in which in an outer

Tube made of a carbon steel or other high-strength metallic material, a second (inner) tube with an outer diameter that is slightly smaller than the inner diameter of the outer tube and a wall thickness of at least 1 mm is inserted and the inner tube made of another, especially a corrosion-resistant and / or wear-resistant metallic material and in which the outer tube is reduced in diameter by forced passage through a reducing ring so that the outer tube shrinks mechanically onto the inner tube in the sense of a press fit, characterized in that the reduction in the diameter of the outer tube is driven only so far in the reducing ring that the mechanical deformation of the inner tube caused by the shrinking of the outer tube onto the inner tube still remains in the elastic range.

2. The method according to claim 1, characterized in that the passage of the reducing ring is carried out by pressing the outer tube in the direction of the tube longitudinal axis.

3. The method according to claim 2, characterized in that the pressing is carried out on an Erhardt drawing press.

Method according to claim 1, characterized in that the reducing ring is passed by pulling.

5. The method according to any one of claims 1 to 4, characterized in that the end faces of the composite tube produced are welded gas-tight after mechanical processing in the annular region of the connection point between the outer and the inner tube.

6. The method according to any one of claims 1 to 5, characterized in that a seamless or a longitudinally welded tube is used as the outer tube.

7. The method according to any one of claims 1 to 6, characterized in that a seamless or a longitudinally welded tube is used as the inner tube.

8. The method according to any one of claims 1 to 7, characterized in that a martensitic chrome steel, a duplex steel or an austenitic stainless steel is used for the outer tube.

9. The method according to any one of claims 1 to 8, characterized in that a martensitic chrome steel, a duplex steel, a ferritic or austenitic stainless steel, titanium or a titanium alloy or a nickel-based alloy is used for the inner tube.

10. The method according to any one of claims 1 to 9, characterized in that a high-temperature alloy is used for the inner tube.

11. The method according to any one of claims 1 to 10, characterized in that a tube with a significantly thicker wall thickness than the inner tube is used for the outer tube.

12. The method according to claim 11, characterized in that the wall thickness of the outer tube is at least 3 mm.

13. The method according to any one of claims 1 to 12, characterized in that the wall thickness of the inner tube is a maximum of 6 mm.

14. The method according to any one of claims 1 to 13, characterized in that the composite pipe is provided on the outside with a corrosion protection coating, in particular with a 3-layer covering made of an epoxy resin base layer, an ethylene copolymer adhesive layer and a final polyethylene cover layer.

15. The method according to any one of claims 1 to 14, characterized in that the connection point of the inner and outer tube is welded gas-tight on the end face.