EP0944443B1 - Process for producing internally plated pipes - Google Patents

Description

The invention relates to a method for producing internally clad pipes, the as composite pipes with an outside diameter of at least 60 mm for Transport of corrosive and / or abrasive fluids (gases, liquids, Suspensions) are provided. This is done in an external, usually thick-walled tube made of a carbon steel or other higher strength metallic material a second (inner) tube with one opposite Inner diameter of the outer tube is slightly smaller and a wall thickness of at least 1 mm. The inner tube consists of another, especially a corrosion-resistant and / or wear-resistant metallic material and generally has a thinner Wall thickness than the outer tube. Between the inner and outer tube becomes a press fit by mechanical shrinking frictional connection created by the diameter of the outer tube is reduced in that this tube by a reducing ring is forced through. (see e.g. GB-A-2 085 330).

Clad pipes are composite components, which are used accordingly their purpose by combining two different materials technical and / or economic advantages can be achieved. Most of the time you want them good corrosion-chemical properties of high-alloy steels with the superior mechanical properties of e.g. B. connect carbon steels. But also the combination of particularly wear-resistant materials with common ones Structural and stainless steels can bring technical and economic advantages. The Economy follows from the fact that the layer thicknesses of the mostly very expensive plating materials on the technical for the respective application necessary dimension can be reduced.

With the increasing exhaustion of the easily accessible deposits of hydrocarbons, the handling of so-called acidic products has increased significantly, particularly in the offshore industry. These products are oil, gas or condensate with proportions of CO 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 further exacerbates the problem of corrosion.

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 appropriate 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 occurs and, if necessary, additionally Corrosion wear on. For such tasks are therefore often used corresponding composite pipes equipped with wear-resistant inner cladding used. The plating is often applied by welding plating. This The process is very complex.

The composite pipes considered here are basically pipes, whose wall consists of two layers of different material composition consists. A distinction is made between pipes with a metallurgical bond Layers of those with a purely mechanical bond (so-called soundproof Links). Composite pipes of the first type can be made using the known methods of coextrusion, roll cladding, hot isostatic pressing, des Explosive plating or welding plating can be produced. A disadvantage of composite pipes, which are manufactured by means of hot forming, is common to be seen in the fact that after the forming the usage properties of basic and support material are not in an optimal condition. For setting z. B. the required mechanical properties of a carbon steel existing carrier material and the corrosion-chemical properties of the a plating material consisting of a high-alloy material is therefore often one additional heat treatment required. This provides one for the carrier material Tempering treatment and solution annealing treatment for the plating material Inevitably, both treatments must and can take place simultaneously Therefore, it must not be carried out in an optimal way for each layer a compromise in temperature control can be found.

Various are available for the production of composite pipes with mechanical connection Process known. There are two different ways to do this. In both Cases are each made of an inner tube with a higher quality one as a rule Material originated in an outer tube with generally larger Wall thickness is inserted from lower 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 against the outer tube expanded to produce the mechanical bond. For example by means of a hydraulic expansion and calibration press, as is done from the Company brochure "PRODUCT - BUTTING BIMETAL PIPES" is known. With this Processes can also produce composite pipes with larger diameters.

In a second method, the mechanical bond between the inner and outer tube manufactured in that a Reduction in diameter of both pipes is enforced by the fact that these pulled together by a drawing ring. This can be done without simultaneous An inner tool is used, as is known from US 4125924. It can also be arranged at the same time in the deformation area of the drawing ring Plugs can be used as an internal tool, as is known from US 386338 is. In this document, a method is also described as a further method of production, at which is similar to the use of a hydraulic expansion press to expand the Inner tube against the outer tube using a pull plug.

It is common to all these processes that in the manufacture of the mechanical Composite both the inner and the outer tube of a plastic Is subjected to deformation.

A method is known from Japan in which the mechanical bond between inner and outer tube is made by an outer Carbon steel tube expanded by thermal expansion and the inside thin-walled tube is hydraulically expanded from the plating material. To Cooling down the outer tube results from shrinking the outer tube Press fit between the inner and outer tube.

The advantages of composite pipes with a purely mechanical connection between the inside and the outer tube are in particular in the opposite composite pipes metallurgical bond significantly lower manufacturing costs. One disadvantage is that limited further processability, for example in hot forming into pipe bends to see. In addition, care must be taken that in the contact zone No moisture penetrates between the inner and outer tube, which too Corrosion could result. The latter, however, only plays in front of the Laying such a composite pipe a role.

In the known methods for producing mechanically connected composite pipes brings the plastic deformation of an inner high-alloy pipe significant disadvantage with itself. This is because of the plastic Deformation the corrosion resistance is adversely affected. This is especially with regard to the resistance to stress corrosion cracking of Importance.

The object of the invention is a generic manufacturing method for mechanical to propose bound composite pipes in which the corrosion resistance of the inner tube especially with regard to stress corrosion cracking as possible high level reached.

This object is achieved according to the invention in a generic method in that, when a reducing ring is forced to pass, through which the outer tube is conveyed with the inner tube therein, the Reduction of the diameter of the outer tube is only driven so far that caused by shrinking the outer tube onto the inner tube mechanical deformation of the inner tube still remains in the elastic range. The Forces acting on the inner tube from the outer tube are during the Deformation is so limited that the inner tube does not undergo plastic deformation is exposed. This leaves its good corrosion-chemical properties completely preserved.

Larger pipe diameters are passed through the reducing ring expediently in that the outer tube in the direction of the tube axis the reducing ring is pushed through. This is preferably done on an Erhardt drawing press. Especially with smaller pipe diameters, the passage of the Reducing ring can also be done in a manner known per se by pulling.

• Innendurchmesser des Reduzierrings am Ausgang
• Außendurchmesser des eingesetzten äußeren Rohres
• Wanddicke bzw. Innendurchmesser des eingesetzten äußeren Rohres
• Außendurchmesser des eingesetzten inneren Rohres.

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
• Outside diameter of the outer tube used
• Wall thickness or inner diameter of the outer tube used
• Outside diameter of the inner tube used.

When reducing the outer tube, the deformation must be set so that the new inner diameter of the outer tube taking into account a sufficient preload (press connection between inner and outer tube) corresponds to the outer diameter of the inner tube. The original Existing air gap between the inner and the outer tube must therefore be completely closed.

For the inner and the outer tube, in particular seamless or longitudinally welded pipes are used. Metallic pipes with helical welds are less preferred. As materials for the outer tube come martensitic as well as usual carbon steels Chrome steels, duplex steels or in special cases also austenitic or ferritic Stainless steels in question. In comparison, the materials for the inner tube are in the Usually higher value; there are especially martensitic chrome steels, Duplex steels, austenitic stainless steels, titanium or titanium alloys and finally also nickel-based alloys in question. In special cases, the inner tube also be formed from a high-temperature alloy. Preferably that outer tube has a wall thickness that is significantly above the wall thickness of the inner Rohres lies. In an expedient embodiment of the invention, the Wall thickness of the outer tube at least 3 mm and its outer diameter at least 110 mm. The wall thickness of the inner tube should be made in particular For cost reasons, even with large-format pipes, if possible, not more than 6 mm be. Around the outer tube, especially if it is made of carbon steel to protect against corrosion, it is preferred to use the composite pipe on the outside to provide a corrosion protection coating. A particularly useful one Execution of the corrosion protection provides a three-layer insulation with a Epoxy resin base layer, an ethylene copolymer adhesive layer and one final polyethylene top layer. But it can also, for example Epoxy resin thick layer insulation or bitumen coatings can be applied. The composite pipes produced according to the invention are on their end faces finally mechanically expediently processed and then in annular area of the junction between the outer and inner tube welded gas-tight, so that none during storage or during transport Moisture penetrate into the bond area between the inner and outer tube can.

Based on the single figure, a composite pipe in the form of a sectional view Shows deformation range of a drawing ring, the invention is closer below explained. In an outer tube 1 is an inner tube 2, the outer diameter is somewhat smaller than the inner diameter of the outer tube telescopically inserted. The inner surface of the outer tube and the outer surface of the inner tube are pure metallic and were possibly pushed into each other cleaned accordingly. This loose unit made of outer tube 1 and inner tube 2 is then e.g. hydraulically driven stamp 3, the expediently a mandrel for coaxial centering of the inner Has tube 2, pressed through a stationary mounting ring 4. 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 so far that there is a bias with respect to the outer surface of the inner tube 2, this preload is so limited, however, that the deformation of the inner Tube 2 remains in the elastic range. The in the inventive method The plastic deformation that takes place therefore remains only on the outer tube 1 limited. Due to the resulting interference fit between the outer tube 1 and the inner tube 2 is formed a so-called soundproof composite.

The main advantage of the method according to the invention over the known method described, such as a hydraulic expansion of the Using the inner tube to achieve the mechanical bond lies in the considerable simpler process control and in the fact that the inner tube is none undergoes plastic deformation. In this way, the previously e.g. by a Solution annealing set optimal corrosion-chemical properties of the Inner pipe also completely preserved on the finished composite pipe. Furthermore the method according to the invention is suitable for the production of composite pipes in a very wide range of dimensions. Especially large format pipes with Outside diameters up to 660 mm and wall thicknesses of the outer tube up to 35 mm can be generated easily. In doing so, existing ones Production facilities, such as an Erhardt drawing press, without large ones Capital expenditure can be used, especially for diameter reduction Standard tools can be used.

Another advantage of the method according to the invention lies in the fact that the plastic deformation behavior of the inner tube material does not matter plays. This allows a very large number of tube material combinations. in the In contrast, in processes in which the mechanical bond through Internal expansion is achieved, the plastic deformation properties of the involved pipe materials to be coordinated. For example, the remaining plastic deformation of the outer tube may be smaller than that of the Inner tube to create a gap-free bond. With approximately the same modulus of elasticity of the two composite materials depends on the level of the yield strength and / or the further course of the hardening curves (stress-strain curves) on. For example, with approximately the same yield strengths of the outer and Inner tube materials, the hardening curve for the latter is flatter than those for the outer tube material to create a tight press fit. This Demand limits in processes that improve the mechanical bond through plastic Deformation of both pipes, the selection of suitable pipe materials. This is not the case with the present invention.

Claims (15)

1. Method of manufacturing internally plated 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 is inserted in an outer pipe composed of a carbon steel or other high-strength metal material, a second (inner) pipe with a slightly smaller outer diameter than the inner diameter of the outer pipe and a wall thickness of at least 1 mm and the inner pipe consists of another, in particular corrosion-resistant and/or abrasion-resistant metal material and in which the outer pipe is sufficiently reduced in diameter by the constrained passing over of a reducing ring that the outer pipe shrinks mechanically on to the inner pipe in the form of a force fit, characterised in that the reduction in diameter of the outer pipe in the reducing ring is only taken so far that the mechanical deformation of the inner pipe effected by the shrinking of the outer pipe on to the inner pipe still remains within the elastic range.
2. Method according to claim 1, characterised in that the passing over of the reducing ring is effected by pressing the outer pipe in the direction of the pipe longitudinal axis.
3. Method according to claim 2, characterised in that the pressing is effected on an Erhardt drawing press.
4. Method according to claim 1, characterised in that the passing over of the reducing ring is effected by drawing.
5. Method according to one of claims 1 to 4, characterised in that the end faces of the composite pipe produced, after mechanical processing in the annular region of the joining point between the outer and the inner pipe are welded in a gas-tight manner.
6. Method according to one of claims 1 to 5, characterised in that as an outer pipe a pipe which is seamless or has a longitudinal weld seam is used.
7. Method according to one of claims 1 to 6, characterised in that as an inner pipe a pipe which is seamless or has a longitudinal weld seam is used.
8. Method according to one of claims 1 to 7, characterised in that for the outer pipe a martensitic chromium steel, a duplex steel or an austenitic special steel is used.
9. Method according to one of claims 1 to 8, characterised in that for the inner pipe a martensitic chromium steel, a duplex steel, a ferritic or austenitic special steel, titanium or a titanium alloy or a nickel-based alloy is used.
10. Method according to one of claims 1 to 9, characterised in that for the inner pipe a high-temperature-resistant alloy is used.
11. Method according to one of claims 1 to 10, characterised in that for the outer pipe a pipe with a significantly thicker wall than the inner pipe is used.
12. Method according to claim 11, characterised in that the wall thickness of the outer pipe is at least 3 mm.
13. Method according to one of claims 1 to 12, characterised in that the wall thickness of the inner pipe is 6 mm maximum.
14. Method according to one of claims 1 to 13, characterised in that the composite pips is provided on the outside with a corrosion-protection coating, in particular with a 3-layered jacket of an epoxy resin base layer, an ethylene copolymer adhesive layer, and a final polyethylene covering layer.
15. Method according to one of claims 1 to 14, characterised in that the joining point of the inner and outer pipes is welded at the end in a gas-tight manner.

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