PROCESS FOR PRODUCING CORROSION RESISTANT ALLOY CLAD METAL PIPES

Abstract

The present invention relates to a process for producing corrosion resistant alloy-clad metal pipes by: (a) providing one or more pipes to be clad; (b) providing an exothermic mixture; 5 (c) loading and distributing the exothermic mixture into the one or more pipes in a cladding assembly at a rotational speed suitable to generate a centrifugal force of at most 10 times the gravitational force; (d) igniting the loaded exothermic mixture using an ignition system at a rotational speed generating a centrifugal force of at least 50 times the gravitational force; 10 and (e) applying a post cladding pipe procedure.

Claims

1. A process for producing corrosion resistant alloy-clad metal pipes by: (a) providing one or more pipes to be clad; (b) providing an exothermic mixture; (c) loading and distributing the exothermic mixture into the one or more pipes in a cladding assembly at a rotational speed suitable to generate a centrifugal force of at most 10 times the gravitational force; (d) igniting the loaded exothermic mixture using an ignition system at a rotational speed generating a centrifugal force of at least 50 times the gravitational force; and (e) applying a post cladding pipe procedure.

2. The process according to claim 1, wherein the corrosion resistant alloy comprises stainless steels, copper-nickel alloys, cobalt super alloys or nickel super alloys.

3. The process according to claim 1, wherein an end cap having a center opening is attached to at least one end of the steel pipe, preferably to both ends of the steel pipe prior to loading.

4. The process according to claim 1, wherein the exothermic mixture comprises at least one transition metal oxide and at least one fuel.

5. The process according to claim 1, wherein the exothermic mixture further comprises other metals or alloys or their oxides, other oxides or fluorides.

6. The process according to claim 1, wherein the clad pipes as obtained in step (d) are contacted with a cooling medium.

7. The process according to claim 6, wherein the cooling medium is water, preferably a water spray or a water tank placed underneath the cladding assembly.

8. The process according to claim 1, wherein the transition metal oxide is selected from the group consisting of copper oxides, iron oxides, nickel oxide, chromium oxides, niobium oxides, cobalt oxides or molybdenum oxides, and tungsten oxides, and mixtures thereof.

9. The process according to claim 1, wherein the exothermic mixture further comprises as fuel a component selected from the group consisting of aluminium, calcium, magnesium, silicon and mixtures thereof, more preferably binary, ternary, or quaternary fuels selected from Al, Ca, Mg and Si, even more preferably binary, ternary, or quaternary fuels comprising at least Ca.

10. The process according to claim 1, wherein the exothermic mixture further comprises a metal selected from the group of copper, iron, nickel, chromium, cobalt, manganese, molybdenum, niobium, tantalum, tungsten, and the alloys thereof.

11. The process according to claim 1, wherein step (c) is performed using blade powder spreading, interior tubing, expandable interior cylinder, and/or rotational velocity variation.

12. The process according to claim 1, wherein the cladding assembly includes mechanical support, an ignition system, and a cooling system.

13. The process according to claim 12, wherein the mechanical support includes a spring shock loaded mechanism to dynamically position and confine the pipe in rotation by confining wheels.

14. The process according to claim 1, wherein green pellets prepared by uniaxial pressing of the exothermic mixture, resistant wire, and a power supply are placed inside the pipes.

15. The process according to claim 1, wherein loading the exothermic mixture to the steel pipes is performed at a rotational velocity generating a centrifugal force of at least 1 g, more preferably at least 2 g and at most 10 g, more preferably at most 8 g.

16. The process according to claim 1, wherein igniting the exothermic mixture using an ignition system is performed at a rotational velocity generating a centrifugal force of at least 100 g, preferably at least 150 g.

17. The process according to claim 1, wherein the cladding assembly comprises an array of water spraying nozzles.

18. The process according to claim 1, wherein the post-cladding pipe procedure includes subjecting the slag layer to a mechanical ablative treatment, including breaking off slag by mechanical means, more preferably by mechanical means assisted by thermal shock due to cooling water spraying and/or by surface machining.

19. The process according to claim 1, wherein the interior of the one or more pipes are subjected to a thorough cleaning step prior to the cladding comprising by sand blasting and/or by using a chemical wash treatment followed by drying.

20. The process according to claim 19, wherein the chemical wash treatment comprises contacting the steel pipe surface with a weak acid, preferably acetic acid, more preferably in an aqueous solution.

21. The process according to claim 20, wherein the concentration of the acetic acid is between 1 and 10 vol %, preferably between 4 and 6 vol %.

Description

[0057] The following, non-limiting embodiments of the invention are further described hereinafter with reference to the accompanying figures, wherein like letters and numerals refer to like parts, wherein the figures are approximately to scale, and wherein:

[0058] FIG. 1 illustrates an example of a cladding operation that is carried out in a centrifugal assembly.

[0059] FIG. 2 illustrates an example of an assembly that is used to spread and compact the powder mixture.

[0060] FIG. 3 illustrates an example of a paper tube that is placed inside at the centre of the pipe.

[0061] FIG. 4 illustrates an example of an ignition set up.

[0062] FIG. 5 illustrates the cross section of the clad pipe.

[0063] FIG. 1 illustrates an example of the cladding operation that is carried out in a centrifugal assembly. The centrifugal assembly is comprised of modules with the number of modules scalable with pipe length. In this non-limiting embodiment each module includes a structural platform (10) which hosts four steel wheels (20). The backing pipe (30) is placed onto the four wheels (20), and the pipe (30) is confined on top by four steel wheels (40) which are mounted to the structural frame using two shocks comprised of spring and dashpot mechanisms (50). Each spring shock can apply force to the clad pipe independently, thus enabling low resistance confinement of rotating eccentric pipes. Other wheel configurations for the module could also be used such as four lower wheels and two upper wheels or a minimal configuration of three wheels such as two lower wheels and one upper wheel. On each end of the backing pipe (30), there is an end cap (60) with an opening in the middle for ignition and for outgassing. One of the wheels on the bottom of the structural platform is driven by a motor (70), which is controlled by a variable frequency drive (VFD) (80) to vary the RPM of the motor. Some modules may not include their own motor and the motor may be controlled by other methods such as gearing or fuel intake. Underneath the bottom four wheels (20) there is a water quenching line (90) for cooling after the combustion synthesis reaction. The water quench line is fed by a pump and contains nozzles and a long enough line to have a spray reach that would extend out to the end of the pipe or the spray reach of the adjacent module to allow for uniform quench. Thus, it is preferred that the cladding assembly includes mechanical support, an ignition system and a cooling system. It is furthermore preferred that the mechanical support includes a spring shock loaded mechanism to dynamically position and confine the pipe in rotation by wheels.

[0064] Prior the clad operation, the backing pipe is preferably prepared by removing rust and grease at the interior surface by for example sandblasting and/or by soaking the pipe in a 5% vinegar solution for at least 24 hours, following by water cleaning and drying.

[0065] The clad operation starts with placing the backing pipe (30) between the four wheels (20) and (40), and the exothermic powder mixture is loaded into the pipe and distributed by one of two methods. In the first method, the powder mixture is first loaded to the inside of the pipe, which is then rotated at a rotational speed, at a rotation per minute (RPM) corresponding to the generation of a gravitational force of 2 g or higher. A device consisting of a blade (110) made of steel (or any other material), guide tracks (120) and adjusting screw (130) as illustrated in FIG. 2 is used to spread and compact the powder mixture. At first, the blade (110) is adjusted to be parallel to the inner surface longitudinally, and then lowered to the powder mixture while the pipe is in rotation at a rotational speed corresponding to generate a gravitational force of at least 2 g. The blade will initially contact the highest areas of the powder and will spread these areas to lower areas. The blade is further lowered down to continue spreading until there is accumulation of powders near the blade edge. This operation ensures that all areas are sufficiently filled with powder and assists in compaction of the powder mixture. The blade is then slowly raised up until the accumulation of powder near blade edge disappears. This method is referred to as the Blade Powder Spreading (BPS) in this document. In some situations, the rotational speed is intentionally increased to generate 10 g or higher in order to increase the packing density of the mixture. Other spreading devices such as a rod or roller may also be used to increase the amount of powder compaction.

[0066] In the another method, a combustible, e.g. paper, wax or carton tube (210) is placed inside at the centre of the backing pipe (220) as illustrated in FIG. 3. The outside diameter (OD) of the paper tube (210) is determined according to the mass and packing density of the powder mixture such that the amount of the powder mixture required to fill the space between the paper tube and backing pipe would form the required clad thickness. The powder mixture is then loaded into the gap between the outside diameter of the paper tube and inside diameter of the backing pipe. The powder mixture pre-loaded backing pipe is then placed onto the cladding assembly between the four wheels (20) and (40) for subsequent cladding operation. This powder mixture loading is referred to as the paper tube (PT) method. Other methods such as the spray, screw feed, and fluidized powder methods as previously described may also be used.

[0067] In still another method, the powder mixture is loaded to the inside of the pipe. The pipe is then rotated at a rotational velocity in RPMs that generates a gravitational force less than 1 g to allow the powder mixture to tumble initially, then the rotational velocity is increased to higher g-levels until it reached about 4 g. The rotational velocity is increased slowly and continuously to allow the inner powder to continue to tumble until the powder is distributed with a uniform layer thickness around the inner circumference of the backing pipe. This method is referred to as the RPM variation method.

[0068] Once the powder mixture is loaded to the clad pipe, the rotation of the pipe is increased to a higher rotational velocity to generate a gravitational force of at least 50 g. The powder is then ignited by using a setup illustrated in FIG. 4. It consists of multiple green pellets (310) pressed from the same exothermic mixture as used for cladding or another compatible mixture, ignition coils (320) made of an electrically resistant wire suitable for Joule heating such a tungsten or Kanthal® (trademark owned by Sandvik) wire, and a power supply (330). Each coil holds one pellet, and all ignition coils may be connected electrically to the same power supply. Specific numbers of green pellet/ignition coil pairs are decided from the reaction rate of the exothermic mixture as well as the length of the pipe to be cladded. The essence of the ignition system in FIG. 4 is to attempt to clad the entire pipe at the “same time”. This is not only to save time, but the entire pipe would have a relatively uniform thermal profile. Alternative ignition methods may use a reactive fuse or ignite the mixture from only one or both ends.

[0069] The required rotational velocity during the reaction is selected according to the combustion temperature of the reaction, compositions of the CRA and slag, and the diameter of the pipe. Typically, it is in the range of 500-2000 RPM, generating a gravitational force of 50-300 g depending on the diameter of the pipes.

[0070] Shortly after the completion of the reaction, the pipe is cooled by water quenching, as shown in FIG. 1, by using a water quenching line (90). Cooling time is determined by consideration of energy generated by the exothermic reaction, pipe size, and water spraying rate.

[0071] The final clad pipe is illustrated in FIG. 5. It comprises a slag layer (430), the clad layer (420) comprised of CRA and the backing steel pipe (410).

[0072] The final step of the manufacture process involves removing the slag thus exposing the CRA. In most cases, slag can be easily broken off by mechanical operation. The slag removal can also be assisted by thermal shock, i.e., spraying the slag with water while it is still hot thus cracking and weakening the slag.

[0073] Optionally, the clad pipe may be heat treated post-clad to obtain the desired microstructure and properties for the backing pipe and clad layer.

[0074] The following, non-limiting examples are provided to illustrate the invention. The clad pipe manufacture process is illustrated in the following using stainless steel as CRA examples.

[0075] For all examples except for example 8, a section of X60 carbon steel pipe having an outside diameter of 273.1 mm, a wall thickness of 11.1 mm and a length of 500 mm was cleaned by sand blasting and soaking in 5% white vinegar for 24 hours.

[0076] After loading the different exothermic mixtures, the ignition set up shown in FIG. 4 was used to ignite the mixture.

[0077] For all examples, the pipe was cooled shortly after the completion of the reaction, by spraying water from both inside and outside. Water spraying from inside the pipe leads to the weakening of the slag by thermal shocking, thus the slag could be readily removed from a subsequent mechanical operation.

Example 1

[0078] An exothermic mixture containing iron oxide (Fe.sub.2O.sub.3), calcium (Ca) and aluminum (Al), and alloying metals of chromium (Cr), nickel (Ni), iron (Fe), molybdenum (Mo), silicon (Si), and manganese (Mn) was loaded to the inside of the pipe by the BPS method while the pipe was in rotation at approximately 250 RPM (.sup.˜8 g). Afterward, the rotational velocity was raised to 1150 RPM (.sup.˜185 g) and the mixture was ignited. Shortly after the completion of the reaction, the pipe was cooled by spraying water.

[0079] Upon the ignition and reaction, the mixture formed molten CRA of stainless steel 316L composition and a molten slag of oxides (CaO and Al.sub.2O.sub.3). Owing to the large difference in specific gravities between the CRA and the slag, the CRA was deposited to the inner wall of the X60 backing pipe with the slag on top. Shortly after the completion of the reaction, the pipe was cooled by spraying water from both inside and outside and slag was removed using a separate mechanical operation. Examination of the cross sections of the cladded pipe showed that a strong metallurgical bond had been formed between the cladded layer and the X60 steel backing.

Example 2

[0080] An exothermic mixture containing iron oxide (Fe.sub.2O.sub.3), chromium oxide (Cr.sub.2O.sub.3), calcium (Ca) and aluminum (Al), and alloying metals of chromium (Cr), nickel (Ni), iron (Fe), molybdenum (Mo), silicon (Si), and manganese (Mn) was loaded to the inside of the pipe by the paper tube (PT) method. Afterward, the rotational velocity was raised to 1150 RPM (.sup.˜185 g) and the mixture was ignited. Shortly after the completion of the reaction, the pipe was cooled by spraying water.

[0081] Upon the ignition and reaction, the mixture formed molten CRA of stainless steel 316L composition and molten slag of oxides (CaO and Al.sub.2O.sub.3). Owing to the large difference in specific gravities between the CRA and the slag, the CRA was deposited to the inner wall of the X60 backing pipe with the slag on top. Shortly after the completion of the reaction, the pipe was cooled by spraying water from both inside and outside and slag was removed using a separate mechanical operation. Examination of the cross sections of the cladded pipe showed a strong metallurgical bond had been formed between the cladded layer and the X60 steel backing.

Example 3

[0082] An exothermic mixture containing iron oxide (Fe.sub.2O.sub.3), calcium (Ca) and aluminum (Al), and alloying metals of chromium (Cr), nickel (Ni), iron (Fe), molybdenum (Mo), silicon (Si), and manganese (Mn) was loaded to the inside of the pipe. The powders were tumbled using a rotational velocity that generates a gravitational force of about 0.5 g for 30 seconds. The rotational velocity or rotational speed is then gradually increased to generate a gravitational force of 4 g with about 5 minutes taken to transition from 0.5 g to 4 g. Afterward, the rotational velocity was raised to 1150 RPM (.sup.˜185 g) and the mixture was ignited. Shortly after the completion of the reaction, the pipe was cooled by spraying water.

[0083] Upon the ignition and reaction, the exothermic mixture forms molten CRA of stainless steel 316L composition and molten slag of oxides (CaO and Al.sub.2O.sub.3). Owing to the large difference in specific gravities between the CRA and the slag, the CRA was deposited to the inner wall of the X60 backing pipe with the slag on top. Shortly after the completion of the reaction, the pipe was cooled by spraying water from both inside and outside and slag was removed using a separate mechanical operation. Examination of the cross sections of the cladded pipe showed a strong metallurgical bond has been formed between the cladded layer and the X60 steel backing.

Example 4

[0084] An exothermic mixture containing iron oxide (Fe.sub.2O.sub.3), calcium (Ca) and aluminum (Al), fluorspar (CaF.sub.2) and alloying metals of chromium (Cr), nickel (Ni), iron (Fe), molybdenum (Mo), silicon (Si), and manganese (Mn) was loaded to the inside of the pipe by the BPS method while the pipe was in rotation at approximately 250 RPM (.sup.˜8 g). Afterward, the pipe was rotated at 1150 RPM (.sup.˜185 g) and the mixture was ignited. Shortly after the completion of the reaction, the pipe was cooled by spraying water.

[0085] Upon the ignition and reaction, the mixture forms molten CRA of stainless steel 316L composition and a molten slag made of oxides (CaO and Al.sub.2O.sub.3) and fluoride (CaF.sub.2). Owing to the large difference in specific gravities between the CRA and the slag, the CRA was deposited to the inner wall of the X60 backing pipe with the slag on top. Shortly after the completion of the reaction, the pipe was cooled by spraying water from both inside and outside and slag was removed using a separate mechanical operation. Examination of the cross sections of the cladded pipe showed a strong metallurgical bond has been formed between the cladded layer and the X60 steel backing.

Example 5

[0086] An exothermic mixture containing iron oxide (Fe.sub.2O.sub.3), calcium (Ca), silicon (Si) and aluminum (Al) and alloying metals of chromium (Cr), iron (Fe), nickel (Ni), molybdenum (Mo), and manganese (Mn) was loaded to the inside of the pipe by the BPS method while the pipe was in rotation at approximately 250 RPM (.sup.˜8 g). Afterward, the rotation speed was raised to 1150 RPM (.sup.˜185 g) and the mixture was ignited. Shortly after the completion of the reaction, the pipe was cooled by spraying water.

[0087] Upon the ignition and reaction, the mixture forms molten CRA of stainless steel 316L composition and a molten slag of oxides (CaO, SiO.sub.2 and Al.sub.2O.sub.3). Owing to the large difference in specific gravities between the CRA and the slag, the CRA was deposited to the inner wall of the X60 backing pipe with the slag on top. Shortly after the completion of the reaction, the pipe was cooled by spraying water from both inside and outside and slag was removed using a separate mechanical operation. Examination of the cross sections of the cladded pipe showed a strong metallurgical bond has been formed between the cladded layer and the X60 steel backing.

Example 6

[0088] An exothermic mixture containing iron oxide (Fe.sub.2O.sub.3), nickel oxide (NiO), chromium oxide (Cr.sub.2O.sub.3), calcium (Ca), aluminium (Al), and silicon (Si) and alloying metals of iron (Fe), molybdenum (Mo), and manganese (Mn) was loaded to the inside of the pipe by the BPS method while the pipe was in rotation at approximately 250 RPM (.sup.˜8 g). Afterward, the rotation speed was raised to 1150 RPM (.sup.˜185 g) and the mixture was. Shortly after the completion of the reaction, the pipe was cooled by spraying water.

[0089] Upon the ignition and reaction, the mixture forms molten CRA of stainless steel 316L composition and a molten slag of oxides (CaO, Al.sub.2O.sub.3 and SiO.sub.2). Owing to the large difference in specific gravities between the CRA and the slag, the CRA was deposited to the inner wall of the X60 backing pipe with the slag on top. Shortly after the completion of the reaction, the pipe was cooled by spraying water from both inside and outside and slag was removed using a separate mechanical operation. Examination of the cross sections of the cladded pipe showed a strong metallurgical bond has been formed between the cladded layer and the X60 steel backing.

Example 7

[0090] An exothermic mixture containing iron oxide (Fe.sub.2O.sub.3), calcium (Ca), aluminium (Al) and silicon (Si), and alloying metals of chromium (Cr), nickel (Ni), iron (Fe), molybdenum (Mo), silicon (Si), and manganese (Mn) was loaded to the inside of the pipe by the BPS method while the pipe was in rotation at approximately 250 RPM (.sup.˜8 g). Afterward, a calculated amount of silica (SiO.sub.2) was loaded to the inside of the pipe by the BPS method while the pipe was in rotation. Then the pipe was rotated at 1150 RPM (.sup.˜185 g) and the mixture was ignited. Shortly after the completion of the reaction, the pipe was cooled by spraying water.

[0091] Upon the ignition and reaction, the mixture forms molten CRA of stainless steel 316L composition and a molten slag made of oxides (CaO, Al.sub.2O.sub.3 and SiO.sub.2). Owing to the large difference in specific gravities between the CRA and the slag, the CRA was deposited to the inner wall of the X60 backing pipe with the slag on top. Shortly after the completion of the reaction, the pipe was cooled by spraying water from both inside and outside and slag was removed using a separate mechanical operation. Examination of the cross sections of the cladded pipe showed a strong metallurgical bond has been formed between the cladded layer and the X60 steel backing.

Example 8

[0092] A section of X60 carbon steel pipe having an outside diameter of 273.1 mm, a wall thickness of 11.1 mm and a length of 500 mm was not cleaned and used “as is” although it was exposed to the environment for a few years and contained visible rust. An exothermic mixture containing iron oxide (Fe.sub.2O.sub.3), nickel oxide (NiO), calcium (Ca), aluminium (Al) and silicon (Si), and alloying metals of chromium (Cr), iron (Fe), molybdenum (Mo), silicon (Si), and manganese (Mn) was loaded to the inside of the pipe by the BPS method while the pipe was in rotation at approximately 250 RPM (.sup.˜8 g). Afterward, the pipe was rotated at 1150 RPM (.sup.˜185 g) and the mixture was ignited. Shortly after the completion of the reaction, the pipe was cooled by spraying water.

[0093] Upon the ignition and reaction, the mixture forms molten CRA of stainless steel 316L composition and a molten slag made of oxides (CaO, Al.sub.2O.sub.3 and SiO.sub.2). Owing to the large difference in specific gravities between the CRA and the slag, the CRA was deposited to the inner wall of the X60 backing pipe with the slag on top. Shortly after the completion of the reaction, the pipe was cooled by spraying water from both inside and outside and slag was removed using a separate mechanical operation. Examination of the cross sections of the cladded pipe showed a strong metallurgical bond has been formed between the cladded layer and the X60 steel backing.

[0094] The above examples for manufacture of stainless steel 316L cladded pipes can be extended to the manufacturing of other CRA clad pipes such as other stainless-steel compositions, nickel super alloys, and copper nickel alloys using appropriate transition metal oxides, thus manufacture of these CRA cladded pipes are also included in the scope of the current invention.