Abstract:
A method of making a compression based tubular structure having at least one structural joint using the friction welding process to improve the durability of tubular structures and structural integrity via increased resistance to tension and fatigue type loading and resistance to corrosion. A method of making a compression based tubular structure having at least one structural joint using the friction welding process is provided. In addition, a compression based tubular structure is provided. The compression based tubular structure comprises at least one tubular structure joint, at least one pair of flanges that surround each tubular joint, and a plurality of tension rods that connect the pair of flanges that surround the tubular structure joint.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    In one embodiment, the present invention relates to a method for making compression based tubular structures using friction welding. In another embodiment, the invention pertains to a method for making compression based tubular structures, such as risers for the oil-drilling industry, sleeves for cannons and any other compression based tubular structures that are friction welded. In a further embodiment, compression based tubular structures may consist of pipes/tubes that are joined end to end, pipe/tube to flange ends that are joined end to end and/or pipe/tube to hollow-end cap that are joined end to end by friction welding for use between a well platform and an oil well or gas well located on the sea floor. 
         [0002]    When an oil well or a gas well located on the sea floor is drilled from a platform, steel pipes of a predetermined length are connected together, end to end to form a casing tube which is lowered from the platform to the sea floor. The casing tube forms a conduit between the platform and the gas or oil well on the sea floor beneath the platform. The casing tube is initially used when the well is being drilled and, thereafter, it is used to bring the crude oil or gas from the sea floor up to the platform. Since the oil well or gas well is located at the bottom of the sea which can be thousands of meters below the platform, the casing tube can have a length of thousands of meters. 
         [0003]    In general, the casing tube used today extends from a platform to the sea floor is made of carbon steel pipes each having a predetermined length of about 10 to 15 meters and which are joined by any one of known methods such as a bolting joining method, a welding method. Because the casing tube which extends from the platform to the sea floor can have a length of thousands of meters, the carbon steel pipes of the casing tube near the surface of the sea and immediately below the platform must support the pull of the total weight of all the carbon steel pipes that are attached to it. In addition, the horizontal tidal flow of the water between the sea bottom and the platform subjects the casing tube to an additional pulling force. Thus, the pipes at and near the top of the casing tube are subjected to a very large pulling force. 
         [0004]    In many instances, if no corrective measures are taken, this pulling force may be sufficient to stretch the carbon steel pipes near the top of the casing tube beyond their elastic limit and possibly lead to their catastrophic failure (e.g. rapture of seams, and joints such as welds). 
         [0005]    Currently, to reduce the pulling force on the carbon steel pipes of the casing tube, floatation members, like buoyancy compensators, are attached to the carbon steel pipes of the casing tube. The flotation members are used to provide an upward force which helps to reduce the destructive down ward pull on the carbon steel tubes of the casing tube. 
         [0006]    In one embodiment, the present invention discloses a method of making a compression based tubular structure using the friction welding process that provides very strong and reliable welds between the different segments of such structures (e.g. Risers), which in turn affords the use of thinner and lighter pipes. In another embodiment, the method of making a compression based tubular structure using friction welding to withstand the pulling force on the compression based tubular structure. In another embodiment, this method may be used to weld different alloys to each other. 
       SUMMARY OF THE INVENTION 
       [0007]    In one embodiment, the present invention provides a method for of making a compression based tubular structure using friction welding that improves the durability and structural integrity of tubular structures via increased resistance to tension and fatigue types of loading and in some cases resistance to corrosion. The method comprises machining square a first end and a second end of a first pipe, machining square a first end and a second end of a second pipe, friction welding the second end of the first pipe to the first end of the second pipe to create a joint, machining square the first end of the first pipe and the second end of the second pipe, machining square a flanged-end of a flange, friction welding the flanged-end of the flange to the first end of the first pipe to create a second joint, machining square the second end of the second pipe, machining square a flanged-end of a second flange, friction welding the flanged-end of the second flange to the second end of the second pipe to create a third joint, and connecting a plurality of tension rods between the flange and the opposite second flange where the compression based tubular structure has at least one structural joint using the friction welding process. 
         [0008]    In another embodiment, the method comprises machining square a first end and a second end of a first pipe, machining square a first end and a second end of a flange, friction welding the first end of the first pipe to the second end of the flange to create a joint, machining square a first end and a second end of the second pipe, machining square a first end and a second end of a second flange, friction welding the second end of the second pipe to the first end of the second flange to create a second joint, machining square the second end of the first pipe, machining square the first end of the second pipe, machining square the first end of the flange, machining square the second end of the second flange, and friction welding the second end of the first pipe to the first end of the second pipe to create a third joint, and connecting a plurality of tension rods between the flange and the second flange, wherein the compression based tubular structure has at least one structural joint using the friction welding process. 
         [0009]    In another embodiment, a rotational stop is used for aligning the orientation of the flanges. In a further embodiment, holes are drilled in the flanged-end of one of the flanges of the compression based tubular structure to align the orientation of both flanges. 
         [0010]    In yet another embodiment, the compression based tubular structure is friction welded to at least one other compression based tubular structure. 
         [0011]    In another embodiment, the tension rods are made of composite, fiberglass, or metal. 
         [0012]    In another embodiment, the compression based tubular structure is encased in a buoyancy-compensator. 
         [0013]    In yet a further embodiment, the present invention discloses a compression based tubular structure comprising at least one tubular structure joint, at least one pair of flanges that surrounding each tubular joint, and a plurality of tension rods that connect the pair of flanges that surround the tubular structure joint. 
         [0014]    Accordingly, it is one embodiment of the invention to provide a method for making compression based tubular structures using friction welding that create highly reliable and consistent weld quality and great performance with decreased weight load by using thinner pipes. 
         [0015]    It is another embodiment of the invention to provide a method for making compression based tubular structures by welding various different alloys to each other. 
         [0016]    These and other further embodiments of the invention will become more apparent through the following description and drawing. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0017]    For a fuller understanding of the invention, reference is made to the following description taken in connection with the accompanying drawing(s), in which: 
           [0018]      FIG. 1  is a perspective view of a tubular structure pre-stressed to be in compression in accordance with the invention; 
           [0019]      FIG. 2  is a sectional view showing a flange and the end of a pipe prior to the flange being friction welded to the pipe; 
           [0020]      FIG. 3  is a sectional view of two sections of a pipe being friction welded together to form a single pipe having a desired length; 
           [0021]      FIG. 4  is a side view of a plurality of pre-stressed pipes assembled to form a tubular structure/casing tube; 
           [0022]      FIG. 5  is a side sectional view of two flanges of the ends of two pre-stressed pipes of a casing tube coupled together; 
           [0023]      FIG. 6  is an end view of a flange showing the various apertures contained therein; 
           [0024]      FIG. 7  is a perspective view of a compression based tubular structure in accordance with another embodiment of the present invention; 
           [0025]      FIG. 8A  is a side view of the compression based tubular structure where a flange is integral with one end of this structure; 
           [0026]      FIG. 8B  is an exploded view of a compression based tubular of  FIG. 8A ; 
           [0027]      FIG. 9  is an end view of another type of flange showing the various apertures contained therein in accordance with another embodiment of the present invention; 
           [0028]      FIG. 10  is a cross-sectional view of the tension rod connected to the flange; and 
           [0029]      FIG. 11  is a perspective view of a compression based tubular structure that is encased in a buoyancy compensator in accordance with the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0030]    The present invention discloses a method for making compression based tubular structures using friction welding that results in improving the reliability of welds, corrosion resistance and decreasing the weight load of a tubular structure. The method of making the compression based tubular structure comprises machining square a first end and a second end of a first pipe, machining square a first end and a second end of a second pipe, friction welding the second end of the first pipe to the first end of the second pipe to create a joint, machining square the first end of the first pipe and the second end of the second pipe, machining square a flanged-end of a flange, friction welding the flanged-end of the flange to the first end of the first pipe to create a second joint, machining square the second end of the second pipe, machining square a flanged-end of a second flange, friction welding the flanged-end of the second flange to the second end of the second pipe to create a third joint, and connecting a plurality of tension rods between the flange and the second flange, where the compression based tubular structure has at least one structural joint using the friction welding process. 
         [0031]    In another embodiment, the method comprises machining square a first end and a second end of a first pipe, machining square a first end and a second end of a flange, friction welding the first end of the first pipe to the second end of the flange to create a joint, machining square a first end and a second end of the second pipe, machining square a first end and a second end of a second flange, friction welding the second end of the second pipe to the first end of the second flange to create a second joint, machining square the second end of the first pipe, machining square the first end of the second pipe, machining square the first end of the flange, machining square the second end of the second flange, and friction welding the second end of the first pipe to the first end of the second pipe to create a third joint, and connecting a plurality of tension rods between the flange and the second flange, where the compression based tubular structure has at least one structural joint using the friction welding process. 
         [0032]      FIG. 1  shows a perspective view of a tubular structure pre-stressed to be in compression by externally located rods that are in tension. More specifically, a compression based tubular structure  20  is made up of a pipe  21  which can have two pipe sections  22 ,  23  joined together at a central located weld or weld seam  24  by friction welding. The ends  25 ,  26  of the pipe sections  22 ,  23  of the pipe  21  are joined by friction welding to flanges  27 ,  28 . The pipe sections  22 ,  23  of the pipe  21  and the flanges  27 ,  28  can be of the same material and alloy or they may be of different materials or different alloys. 
         [0033]    Suitable types of materials for the pipes and flanges that may be used in the present invention include, but are not limited to, aluminum, steel, titanium and/or combinations thereof. For example, the pipe sections can be of aluminum and the flanges can be of aluminum. In the alternative, the pipe sections can be composed of aluminum and the flanges can be composed of steel. The pipe and flange sections may also be composed of a composite such as fiberglass. 
         [0034]      FIG. 1  shows that each flange  27 ,  28  has a plurality of various apertures for different purposes where the various apertures in flange  27  are aligned with cooperating apertures in flange  28 . For example, where pipe  21  has two rods which are used to pre-stress the pipe, each flange will have four alternately spaced apertures where two of the four apertures are sized to receive threaded tension rods and the other two of the four apertures are clearance openings for nuts that are threaded onto the threaded tension rods. In addition, each flange will have four or more apertures located inboard, outboard or on the same circumference as the four apertures for receiving threaded bolts and nuts for clamping the flanges of two pipes together. 
         [0035]    Pipe  21  can consist of a number of individual sections joined together by friction welding. For example, pipe  21  can be a single section, or it can be made from two or more sections joined together by friction welding. The flanges at the ends of the pipe  21  can be separate flanges which are friction welded to the ends of the pipe  21 . In the embodiment where the pipe  21  is made up of two pipe sections  22 ,  23 , the two sections  22 ,  23  can be joined together by friction welding, and a flange can then be attached to each end of pipe  21  by friction welding. It is understood that the order of friction welding the various parts to each other is not critical and in one embodiment the two pipe sections  22 ,  23  are first friction welded to each other, and the flanges  27 ,  28  are then friction welded to the ends of the pipe  21 . In another embodiment, pipe sections  22 ,  23  are first friction welded to flange  28 ,  27 , respectively. Then, the two pipe sections-flange components are friction welded to each other to create the tubular structure. 
         [0036]    The ends of the parts to be friction welded are first machined square for cleanliness so that they are nearly perfectly parallel to each other and perpendicular to the neutral axis of the pipes being friction welded and the axis of friction welding. 
         [0037]      FIG. 2  shows a sectional view of a flange and the end of a pipe prior to the flange being friction welded to the pipe. 
         [0038]      FIG. 3  shows a sectional view of two sections of a pipe being friction welded together to form a single pipe having a desired length. Pipe section  22  has a first end  32  and a second end  33 . Pipe section  23  has a first end  34  and a second end  35 . The first end  32  of pipe section  22  is butted against a stop member  43  which prevents pipe section  22  from moving to the left, when the axial forging force is applied during the friction welding operation. Positioned around the outside surface of pipe section  22  are locating clamps  43  which function to both accurately locate pipe section  22  so its neutral axis is parallel to the axis of rotation of the other pipe,  23 , during the friction welding operations and to securely clamp pipe section  22  to prevent it from rotating. It is noted that each end of pipe section  22  is machined to be square and free of thick surface oxides (e.g. aluminum oxide, rust), grease and other impurities. Pipe section  23  is positioned to the right of pipe section  22  and is aligned with pipe section  22  such that second end  33  of pipe section  22  and first end  34  of pipe section  23  are aligned with and nearly parallel with each other. Locating clamps  44  are provided to both accurately position and align pipe section  23  with its neutral axis and axis of rotation during friction welding and with pipe section  22  and to firmly clamp section  23  so it can be rotated (spun) by the friction welding machine. Locating clamps  44  are coupled to a rotating member  46  which, in turn, is coupled to a torque motor or a flywheel coupled to rotatably drive the clamps and pipe section  23 . A piston  47  positioned to push the pipe section  23  toward the left is located at the second end  35  of pipe section  23 . Alternatively, the more conventional approach is to incorporate both the mechanism that holds, deploys and retracts clamps  44  and the system  47  to axially push pipe section  23 , towards section  22 , with the rotating member  46 . Prior to positioning pipe section  23  in the locating clamps  44  at the right of pipe section  22 , both ends of pipe section  23  are machined to be square and free of thick oxides, grease and other impurities. In operation, pipe section  23  is rotated by the torque motor or flywheel as second end  33  of pipe section  22  and first end  34  of pipe sections  23  are forced toward each other by the piston  47  until the ends of the pipe sections friction weld together to form weld seam  24  as shown in  FIG. 1 . 
         [0039]    Each end of the pipe  21  is now in condition to be friction welded to a flange. When friction welding a flange to an end of pipe  21 , pipe  21  is clamped in a fixed position and the flange is advanced toward and contacts the end of the pipe  21  as it is rotated relative to the pipe  21 . Thereafter, the pipe  21  is turned around, is fixed in position and the second flange is moved into contact with the end of the pipe as it is rotated to friction weld the other end of the pipe  21  to the flange. When friction welding the second flange to the pipe  21 , an indexing member is used to align the apertures in the first flange friction welded to the pipe section  21  with cooperating aperture in the second flange being friction welded to the pipe section  21 , while a rotational stop is used on the already friction welded subassembly. 
         [0040]      FIG. 4  shows a side view of a plurality of compression based tubular structures assembled to form a casing tube. 
         [0041]    A side sectional view of the flanges on the ends of two compression based pipes clamped together to form a water tight connection is shown in  FIG. 5 . In this embodiment, the flanges are designed to receive two tension rods  40 . 
         [0042]    Referring to  FIGS. 5 and 6 , flange  27  has a plurality of apertures. One group of eight apertures  50  are used for receiving eight threaded bolts  52  and nuts  53 . The bolts  52  and nuts  53  are used to tightly clamp the flanges  28 ,  29  together to provide a solid and water proof connection. Prior to welding the flanges to the pipe, the flanges were machined flat to help provide a water tight seal between the flanges. If desired, a gasket or sealing compound (not shown) can be located between the flanges to insure that the space between the two flanges  28 ,  29  is water tight. In this embodiment, flange  28  is designed to receive four tension rods  40 . Therefore, flange  28  has four apertures  54 , each having a diameter slightly larger than the diameter of the rods  40 , each having a diameter sufficient to freely accept a nut  56  that is attached to the end of a rod  40  of an adjacent pipe  21 . It is understood that the apertures  54  are located on the same circle and that apertures  50  can be located inboard, out board or on the same circle as apertures  54 . In addition, the number of apertures in the flanges for the rods  40  and for the bolts  52  are not fixed. Typically the compression of the tubes will be achieved by three or more tension rods  40   
         [0043]    After the flanges have been friction welded to the pipe  21 , rods  40 , which are threaded at each end, are then inserted into aligned apertures  54  in the flanges  28 ,  29 . The ends of the rods extend through the apertures  54  and a nut  61  (see  FIG. 1  ) is threaded onto each end of the rod  40 . One or both of the nuts are then tightened until the rods are stretched at an amount sufficient to pre-stress the pipe  21  by placing it in compression. Thus, by tensioning the rods and placing them in tension, the pipe  21  is pre-stressed and is placed in compression. 
         [0044]    Referring to  FIG. 4 , there is shown a side view of a number of pipes  21  assembled end to end to form a section of a casing tube  60 . In  FIG. 4 , each pipe  21  has two rods  40  used to pre-stress the pipe  21 . In is understood that the pipes  21  at the top of a casing tube can have three or four or more rods  40  where the forces are the greatest, and the pipes  21  at the bottom of the casing tube can have fewer rods because the forces are less. 
         [0045]    By making each of the pipes of a light weight material such as aluminum, and by pre-stressing each of the pipes  21  to be in compression, a casing tube formed by attaching a plurality of the tubes  21  together end to end can be made which can have a length of thousands of meters for use between a platform and the bottom of the sea which does not require flotation means. 
         [0046]      FIG. 7  shows a perspective view of a compression based tubular structure in accordance with another embodiment of the present invention. Here, flanges  58 ,  59  have four ears. This allows the connection of a plurality of tension rods  70  without taking up the space needed for the holes into or through the existing utility lines, such as compressed air, hydraulic, etc. 
         [0047]    In general, tension rods are made of a material that will be sized and connected to the flanges by mechanical means, in a manner that will permit their repeated flexing and stretching with the tubular structure without yielding and chaffing. Suitable types of tension rods that may be used in the present invention include, but are not limited to, composite, glass fibers, or steel and/or combinations thereof. Each tension rod may also be made of bundles or multiple rods. 
         [0048]      FIG. 8A  shows a side view of the compression based tubular structure where a flange  60  is integral with an end flange  61 .  FIG. 8B  shows an exploded view of flange  60 . 
         [0049]      FIG. 9  shows an end view of another type of flange that may be used in the present invention. Here, flange  58  has four ears with a plurality of apertures. One group of eight apertures  62  are used for receiving eight threaded bolts and nuts (not shown). In this embodiment, flange  58  is designed to receive four rods  70 . Therefore, flange  58  has four apertures  54 , each having a diameter slightly larger than the diameter of the rods  70  each having a diameter sufficient to freely accept a nut  66  that is attached to the end of a rod  70  of an adjacent pipe  72  as shown in  FIG. 7 . It is understood that the apertures  54  are located on the ears of flange  58  and that apertures  62  can be located inboard from apertures  54 . In addition, the number of apertures in the flanges for the rods  70  and for the bolts is not fixed. 
         [0050]      FIG. 10  shows a cross-sectional view of the tension rod connected to flange  60 . Tension rod  70  is connected to end flange  61  through aperture  54  with a washer  77  and a self-locking nut  66 . Aperture  54  has a swivel opening  76  for nut  66  to allow for flexing of tension rod  70 . There is a flared opening  74  opposite swivel opening  76  in aperture  54  to allow flexing and prevent chaffing of the tension rod  70 . 
         [0051]    In another embodiment of the present invention, to protect tension rods from the environment, such as the sea, they are encased by a buoyancy-compensator  78  as shown in  FIG. 11 . 
         [0052]    While specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of the invention which is to be given the full breadth of the appended claims and any and all equivalents thereof.