METHOD OF PRODUCING A TUBE ARRANGEMENT, A TUBE ARRANGMENT AND A FURNACE PROVIDED WITH SUCH A TUBE ARRANGEMENT

Abstract

A tube arrangement includes a first metal tube provided with a first outer threading in an end region thereof, a second metal tube provided with a second outer threading in an end region thereof, a first butt weld joining the end regions of the first and second tubes, and a sleeve provided on the outside of first and second metal tubes forming a thread coupling with the outer threading of the first and second tubes. The present disclosure also relates to a method of producing the tube arrangement, in which a first tube is joined with a second tube, both the first tube and the second tube being metal tubes. A furnace having a chamber, which is provided with a burner arrangement for generating heat and a tube arrangement for conduction of a hot gas or steam through the furnace, is also provided.

Claims

1. A method of producing a tube arrangement, in which a first tube is joined with a second tube, said tubes being metal tubes, wherein said method comprises the following steps: a) providing an end region of the first metal tube with a first outer threading; b) providing an end region of the second metal tube with a second outer threading; c) providing a first sleeve part made of metal with a first inner threading; d) providing a second sleeve part made of metal with a second inner threading; e) positioning the first metal sleeve part on the first metal tube by screwing said first metal sleeve part onto the first outer threading of the first metal tube; f) positioning the second metal sleeve part on the second metal tube by screwing the second metal sleeve part onto the second outer threading of the second metal tube; g) moving the ends regions of the first and second metal tubes into contact with each other; h) butt welding together from the outside the end regions of the first and second metal tubes; i) bringing together the first and second metal sleeve parts (8, 10) by screwing at least one of said metal sleeve parts (8, 10) on the outer threading (2, 5) of an associated tube; and j) butt welding together from the outside the opposed ends of the first and second metal sleeve parts, wherein in step g) the first and second metal sleeve parts are positioned such that a joint between the first and second metal tubes is accessible from outside.

2. The method according to claim 1, wherein before step a) or before step f), at least one of the first and second metal tubes is subjected to a treatment whereby said end region is provided with a larger outer diameter and a larger wall thickness than an adjacent part of the tube.

3. The method according to claim 2, wherein said treatment includes forging of said end region such that said end region is provided with a larger outer diameter and a larger wall thickness than an adjacent part of the tube.

4. The method according to claim 1, wherein between steps g) and h), a protection member is positioned between the first and second metal sleeve parts and the first and second metal tubes, wherein the protection member separates the second butt weld from the first and second metal tubes and from the first butt weld.

5. The method according to claim 4, wherein the protection member is a ceramic.

6. The method according to claim 1, wherein the first metal tube comprises a first metal alloy and the second metal tube comprises a second metal alloy, wherein the first and second metal alloys have different alloy compositions.

7. The method according to claim 6, wherein the first metal alloy is a ferritic steel comprising Fe, Cr and Al, and the second metal alloy is an austenitic steel comprising Fe, Cr and Ni.

8. The method according to claim 1, wherein the first metal sleeve part and the second metal sleeve part are of a same alloy composition.

9. A tube arrangement, comprising a first metal tube provided with a first outer threading in an end region thereof; a second metal tube provided with a second outer threading in an end region thereof; a first butt weld joining said end regions of the first and second metal tubes; a first metal sleeve part provided with a first inner threading and positioned on said end region of the first metal tube; and a second metal sleeve part provided with a second inner threading and positioned on said end region of the second metal tube, wherein the inner threading of the first metal sleeve part engages the outer threading of the first metal tube and wherein the second inner threading of the second metal sleeve part engages the outer threading of the second metal tube and wherein the opposed ends of the first metal sleeve part and the second metal sleeve part are joined by a second butt weld.

10. The tube arrangement according to claim 9, wherein there is a space between the second butt weld and the first and second metal tubes and between the second butt weld and the first butt weld.

11. The tube arrangement according to claim 10, wherein the tube arrangement is provided with a ceramic protection member said space.

12. The tube arrangement according to claim 9, wherein the first metal tube comprises a first metal alloy and the second metal tube comprises a second metal alloy and wherein the first metal alloy and the second metal alloy are of different alloy compositions.

13. The tube arrangement according to claim 9, wherein the first metal sleeve part and the second metal sleeve part are of a same alloy composition.

14. A furnace comprising: a chamber in which there is provided a burner arrangement for generating heat; and a tube arrangement provided in the chamber, for conduction of a hot gas or steam through the furnace, the tube arrangement including a first metal tube provided with a first outer threading in an end region thereof, a second metal tube provided with a second outer threading in an end region thereof, a first butt weld joining the end regions of the first and second metal tubes, a first metal sleeve part provided with a first inner threading and positioned on the end region of the first metal tube, and a second metal sleeve part provided with a second inner threading and positioned on the end region of the second metal tube, wherein the inner threading of the first metal sleeve part engages the outer threading of the first metal tube and wherein the second inner threading of the second metal sleeve part engages the outer threading of the second metal tube, the opposed ends of the first metal sleeve part and the second metal sleeve part being joined by a second butt weld.

15. The furnace according to claim 14, wherein the furnace is a furnace in which ethylene is produced by means of cracking of hydrocarbons conducted by said tube arrangement.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Embodiments of the disclosure will now be presented with reference to the annexed drawing, on which:

[0054] FIG. 1 is a cross section showing a tube arrangement of the present disclosure,

[0055] FIG. 2 is an enlarged view of a detail of the tube arrangement shown in FIG. 1,

[0056] FIG. 3 is a perspective view of the tube arrangement in a position before joining of the first and second metal tubes thereof by means of welding, and

[0057] FIG. 4 is a schematic view of a furnace in which a tube arrangement according to the present disclosure is arranged.

DETAILED DESCRIPTION OF THE DISCLOSURE

[0058] Though the disclosure is applicable to all applications in which an outer sleeve is used for the purpose of supplementing or replacing the load-carrying function of a weld between two metal tubes, the present disclosure will be described with regard to an application in which tubes are used in furnaces for cracking of hydrocarbonaceous feedstock, typically for the production of ethylene. It should thus be understood that the present disclosure is not primarily restricted to such an application.

[0059] FIG. 1 shows a cross section of a tube arrangement of an embodiment of the present disclosure. The tube arrangement comprises a first metal tube 1 provided with an first outer threading 2 in an end region 3 thereof; a second metal tube 4 provided with a second outer threading 5 in an end region 6 thereof; a butt weld 7 joining said end regions 3, 6 of the first and second metal tubes 1, 4; a first metal sleeve part 8 provided with a first inner threading 9 and positioned on said end region 3 of the first metal tube 1, wherein the first inner threading 9 of the first metal sleeve part 8 engages the first outer threading 2 of the first metal tube 1; a second metal sleeve part 10 provided with a second inner threading 11 and positioned on said end region 6 of the second metal tube 4, wherein the second inner threading 11 of the second metal sleeve part 10 engages the second outer threading 5 of the second metal tube 4, wherein opposed ends of the first metal sleeve part 8 and the second metal sleeve part 10 are joined by a butt weld 12. In the present disclosure, the term sleeve is intended to mean a one piece tubular threaded connection.

[0060] Each of the above-mentioned end regions 3, 6 of the first and second metal tubes 1, 4 is provided with a larger outer diameter and a larger wall thickness than an adjacent part of the first and second metal tube 1, 4 associated thereto. The bottom of each threading encircles a circle having a larger diameter than the diameter of said adjacent part of the respective first and second metal tube 1, 4. Accordingly, the inner diameter of the first metal sleeve part 8 is larger than the outer diameter of said adjacent part of the first metal tube 1, and the inner diameter of the second metal sleeve part 10 is larger than the diameter of said adjacent part of the second metal tube 4. The outer diameter of said end region 3 of the first metal tube 1 corresponds to the outer diameter of said end region 6 of the second metal tube 4.

[0061] The opposing ends of the first and second metal tubes 1, 4 that are joined by means of the butt weld 7 are bevelled such that the butt weld 7 is U-shaped, or V-shaped, with its wider end directed outwards.

[0062] The opposing ends of the first and second metal sleeve parts 8, 10 that are joined by the butt weld 12 are bevelled such that the butt weld 12 is U-shaped, or V-shaped, with its wider end directed outwards.

[0063] There is a space 13 between the butt weld of the first and second metal sleeve parts 8, 10 and the first and second metal tube 1, 4 or the butt weld 7 thereof. This space will prevent the butt weld 12 connecting the first and second metal sleeve parts 8, 10 from contacting and interacting with the first and second metal tubes 1, 4 and from contacting and interacting with the butt weld 7 connecting said metal tubes 1, 4. A ceramic protection member 14 is provided in said space 13, preventing the butt weld 12 connecting the first and second metal sleeve parts 8, 10 from contacting and interacting with the first and second metal tubes 1, 4 and the butt weld 7 connecting the latter.

[0064] The first metal tube 1 comprises a first metal alloy and the second metal tube 4 comprises a second metal alloy, wherein there is at least one brittle phase in the butt weld 7 joining the first and second metal tubes as a consequence of the first and second metal alloys have different alloy compositions and thereby different material chemistry, the alloying elements comprised therein will interact and form said phase upon welding, thus making the butt weld 7 mechanically weaker than the respective metal tube 1, 4. Here, the first metal alloy FrCrAl alloy, and the second metal alloy is FeCrNi alloy. The above-mentioned brittle phase may thus include nickel aluminides. In the exemplifying embodiment presented here, the first metal alloy contains, in weight %: C up to 0.08, Si up to 0.7, Cr 10-25, Al 1-10, Mo 1.5-5, Mn up to 0.4, balance Fe and normally occurring impurities.

[0065] The first and second sleeves 8, 10 are made of steel having the same or at least corresponding chemical composition. In the exemplifying embodiment presented here, the metal alloy of the first and second sleeve is the above-mentioned first metal alloy, which contains, in weight %: C up to 0.08, Si up to 0.7, Cr 10-25, Al 1-10, Mo 1.5-5, Mn up to 0.4, balance Fe and normally occurring impurities.

[0066] The second inner threading 11 of the second metal sleeve part 10 presents an alumina layer (not visible on the drawing). The risk of having iron oxide on the surface of threading of the first metal alloy is even larger when the opposing part, in this case the second metal tube 4, is made of the above-mentioned second metal alloy and the second metal sleeve part 10 is formed by the first metal alloy. Therefore, at least the second inner threading 11 of the second metal sleeve part 10 should be subjected to a pre-oxidation treatment and whereby an alumina layer is obtained thereon as a result thereof. In the exemplifying embodiment presented here, the first inner threading 9 of the first metal sleeve part 8 also presents a protecting alumina layer. Also the first outer threading 2 of the first metal tube 1 presents a protective alumina layer.

[0067] The tube arrangement presents a gas-tight connection between the first and second metal tubes 1, 4 defined by the butt weld 7 connecting the first and second metal tubes 1, 4, while a sleeve formed by the first and second metal sleeve parts 8, 10 forms a load-carrying part of the tube arrangement, which reduces the mechanical load needed to be adopted by the butt weld 7 connecting the first and second metal tubes 1, 4. According to the exemplifying embodiment, the load-carrying part formed by the first and second metal sleeve parts 8, 10 connected by the butt weld 12 is designed to carry a larger part of mechanical load to which the tube arrangement is subjected than is carried by the butt weld connecting the first and second metal tubes 1, 4.

[0068] An exemplifying embodiment of the provision of the tube arrangement presented hereinabove comprises the following steps: [0069] providing an end region 3 of the first metal tube 1 with a first outer threading 2; [0070] providing an end region 6 of the second metal tube (4) with an second outer threading 5; [0071] providing a first sleeve part 8 made of metal with a first inner threading (9); [0072] providing a second sleeve part 10 made of metal with a second inner threading 11; [0073] positioning the first metal sleeve part 8 on the first metal tube 1 by screwing said first metal sleeve part 8 onto the first outer threading 2 of the first metal tube 1; [0074] positioning the second sleeve part 10 on the second metal tube 4 by screwing the second metal sleeve part 10 onto the second outer threading 5 of the second metal tube 4; [0075] moving the ends regions 3, 6 of the first and second metal tubes 1, 4 into contact with each other; [0076] butt welding together from the outside the end regions 3, 6 of the first and second metal tubes 1, 4; [0077] bringing together the first and second metal sleeve parts 8, 10 by screwing at least one of said metal sleeve parts 8, 10 on the outer threading 2, 5 of its associated tube 1, 4; [0078] butt welding together from the outside the opposed ends of the first and second metal sleeve parts 8, 10;

[0079] The above-mentioned threading 2, 5, 9, 11 are typically generated by means of machining of the respective component provided therewith.

[0080] The butt welding process is suggested to comprise a TIG (tungsten inert gas)-welding process, possibly manual, using the above-mentioned first metal alloy as the filling material. However, other suitable alloys may also be used as filling material. The filling material may be in the form of a strip or a wire.

[0081] Before providing said end regions 3, 6 of the first and second metal tubes 1, 4 with said outer threading 2, 5, the metal tubes 1, 4 are subjected to a treatment by means of which the end region 3, 6 thereof is provided with a larger outer diameter and a larger wall thickness than an adjacent part corresponding metal tube 1, 4. This treatment comprises a forging step, also referred to as upsetting.

[0082] Before joining by butt welding the opposed ends of the first and second metal sleeve parts 8, 10, the ceramic protection member 14 is positioned between the first and second metal sleeve parts 8, 10 and the first and second metal tubes 1, 4 at a position in which it will prevent the butt weld 12 of the first and second metal sleeve parts 8, 10 from contacting and interacting with the first and second metal tubes 1, 4 and the butt weld 7 connecting them.

[0083] The second inner threading 11 of the second metal sleeve part 10 is subjected to a pre-oxidation treatment before the second metal sleeve part 10 is positioned on the second metal tube and the second metal tube 4 is joined with the first metal tube 1. The pre-oxidation treatment comprises heating the second metal sleeve part 10 to a temperature of approximately 1100 C. for a period of approximately 8 hours.

[0084] In the exemplifying embodiment presented here, also the first inner threading 9 of the first metal sleeve part 8 and the first outer threading 2 of the first metal tube 1 are provided with a alumina layer by means of a corresponding heat treatment.

[0085] FIG. 4 shows a furnace, presenting a chamber 15 in which a burner arrangement 16 is provided for generating heat and in which a tube arrangement as defined hereinabove is provided for conduction of a hot gas or steam through the furnace. In this specific embodiment, the furnace is a furnace in which ethylene is produced by means of cracking of hydrocarbons conducted by said tube arrangement.

[0086] Inside the chamber 15 of the furnace, tubing 19 to which the tube arrangement is connected (here by butt welds 20, 21) is formed by a tubing 19. It is suggested that the above-mentioned first metal alloy is used as the material of said tubing 19. At the region of an outlet 17 of the chamber 15, inside the chamber 15, the above-defined tube arrangement is provided, wherein the second metal tube 4 of the tube arrangement extends out of said chamber 15 through said outlet 17. At an inlet 18 of the chamber 15, inside the chamber 15, another tube arrangement as defined hereinabove is arranged. The second metal tube 4 of this tube arrangement extends out of the chamber through the inlet 18.