Abstract:
The invention comprises a device for expanding tubular members to a controlled diameter and its method of fabrication. The device includes an expandable bladder held in a convoluted form. After the device is inserted into a cylindrical tube to be evenly expanded, the bladder is expanded by hydraulic pressure to a controlled maximum diameter. It is then deflated so the device can then be moved to another location and reused. The bladder is formed from a flexible impervious material having integral reinforcing fibers. It is initially formed in a fully expanded configuration over a convoluted mandrel and a removable cylindrical shell. When the shell is removed vacuum or external pressure draws the bladder against the mandrel. The bladder is overmolded with a resilient cover to hold it in reduced form until pressurized. The bladder cover prevents the bladder from kinking during the expansion.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 60/874,378, filed Dec. 12, 2006 and entitled “Tubular Expansion Device and Method of Fabrication,” which is incorporated by reference herein. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates to an improved tubular expansion apparatus for the controlled expansion of a tube segments and a method of fabrication thereof. The invention has application in a variety of disciplines such as the expansion of tubular casings (“tubulars”) in a well bore, the expansion of tubes in a heat exchanger, or the expansion of repair sleeves in either a heat exchanger or a pipeline, as well as other applications. Current methods of accomplishing these tasks are often ineffective in controlling the expansion of the tubular, risk collapsing the tubular due to axial loads applied to the tubular, or are significantly more expensive or time consuming. 
       BACKGROUND 
       [0003]    The expansion of tube segments or “tubulars” is important in a number of fields, especially in such areas as the oil field industry, heat exchanger industry and pipeline industry. The oil field industry uses expandable casing to complete wells and expandable liners are used to patch holes in existing strings of casing. The pipeline industry also uses expandable liners to patch leaks in existing pipelines or to tie together sections of pipeline under construction. In tubular heat exchangers expansion of a tubular section can be used to seat a tube within a tubesheet or to repair a leak in an existing tube within the heat exchanger. In each of the above-noted industries, a variety of methods have been employed to provide the insitu expansion of tubular sections. These methods can be grouped into three basic categories, explosive expansion, mechanical expansion, and hydraulic expansion. 
         [0004]    Explosive expansion is primarily used in the oil well industry for the completion or repair of existing casing strings. The tubular section to be expanded is lowered into the well on a wire line or tubing string. The tubular is sealed at both ends and contains an explosive charge inside the tubular running the length of the tubular. The charge is detonated and the pressure generated expands the tubular out against the existing casing. The outside is generally sealed to the existing casing with a layer of fiberglass impregnated resin. A mandrel may then be pulled through the expanded liner to complete the expansion process. 
         [0005]    Mechanical expansion of tubulars is also used in well completion, pipeline repair and heat exchanger fabrication and repair. Two primary methods of mechanical expansion are utilized in these various industries; linear swaging and rotary swaging. In the linear swaging method, the tubular is either affixed to the existing casing or is suspended on the wire line or tubing string. A mandrel is then forced through the tubing to expand it. Rotary swaging typically utilizes a cone with external rollers to expand the tubular. The cone is rotated while it is pulled through the tubing decreasing the axial stresses on the tubular as compared to linear swaging but increasing the torsional stresses on it. 
         [0006]    The final method for the insitu expansion of tubulars is hydraulic expansion in which fluid pressure is used to provide the expansion force on the inside of the tubular. Two processes are used to accomplish such expansions. In direct hydraulic expansion, the tubular is sealed at its ends and fluid pressure is applied directly to the inside surface of the tubular section being expanded. In contained hydraulic expansion, the fluid is injected into a resilient member such as a rubber sleeve or bladder and the expansion of the resilient member causes the tubular to be expanded. 
         [0007]    Each of the above methods has shortcomings which are addressed by the current invention. Explosive expansion is both expensive and complicated and the expansion of the tubular is difficult to control. Variations in the ignition of the explosive charge and in the material properties of the tubular section itself can vary the expansion of the tubular in a non-uniform manner and can even lead to rupture of the tubular section. In addition each length of tubing must be individually prepared, sealed off to contain the explosive pressure and lowered into place. An incomplete or uneven explosion can lead to a costly repair operation. 
         [0008]    Current mechanical expansion methods also have shortcomings. With either method, the apparatus subjects the tubular to significant axial or torsional stresses which can lead to buckling of the tubular and thus damaging both the tubular section and the expansion apparatus. Once again costly retrieval operations and repairs can result. Both methods of mechanical expansion can also cause scarring of the internal surface of the tubular during the swaging process making sealing between subsequent lengths of tubing difficult. Because the length of tubular that can be expanded in one downhole operation is limited by the buckling loads imposed on the tubular, the process is both slow and expensive. 
         [0009]    There are also weaknesses in the current methods of hydraulic expansion of tubulars. With direct hydraulic expansion, a tubular section must be sealed at its two ends and this seal must be maintained throughout the expansion process. Sealing methods in use today are complicated and expensive. In addition, since the seal must engage the ends of the tubular section, it is difficult to expand the entire length of the section with this process without damaging the seal. A secondary operation must be performed to expand the ends of the tubular. The ultimate radial expansion of the tubular is also not controlled by this method. If a repair is being made to an existing tube, some portions of the existing tube will restrain the expansion more than other portions resulting in uneven expansion and possible failures in over-expanded areas. Similar problems exist with contained hydraulic expansion since the ultimate expansion of the resilient containment is not properly controlled. These methods are also limited in their ability to expand the tubular at its end since their radial expansion is limited only by the restriction of the expanding tubular section or by the amount of fluid introduced into the resilient sleeve or bladder of the indirect hydraulic expansion process. 
         [0010]    It is an object of the current invention to overcome the shortcomings of the current methods and apparatus described above by providing a device for the expansion of tubular sections that enables limited and controlled uniform expansion. 
         [0011]    A further object of the current invention is to provide a device for the expansion of tubular sections that is easy to use and may be used to expand long sections of tubes or pipes including end sections in a uniform manner that avoids tubular breakage. 
         [0012]    A further object of the current invention is to provide a device for the expansion of tubular sections in an even cylindrical manner that avoids torsional or axial stresses. 
         [0013]    A further object of the current invention is to provide a method of manufacturing a device for the expansion of tubular sections for continuous expansion of tubulars in a uniform manner to a desired diameter. 
         [0014]    Yet a further object of the current invention is to provide a method of expanding tubular pipes in a continuous and uniform manner with reduced scoring or weakening of the tubes. 
         [0015]    Yet a further object of the invention is to provide a method and apparatus for the expansion of tubular end sections that is uniform in strength and diameter to sections removed from the tube end. 
         [0016]    Yet a further object of the invention is to provide a method and apparatus for carrying the casing string into the wellbore and expanding the upper end of the casing string to lock it into place without the need of special tools to hang the casing in the well prior to expansion. 
         [0017]    Finally a further object of the invention is to provide a method and apparatus for the repair and expansion of tubulars that lower the likelihood of difficult repair and retrieval of remote tube sections. 
       SUMMARY OF THE INVENTION 
       [0018]    The foregoing are among the objects achieved by the invention, aspects of which are discussed in the text that follows in this Summary of the Invention. That text, which describes elements, steps and/or other features of some aspects of the invention, is merely provided by way of example and is not intended nor shall it be construed as limiting the invention. Particularly, it will be appreciated that other aspects of the invention comprise individual ones of the elements, steps and/or features described below (as well as elsewhere herein), as well as various combinations and subcombinations thereof. 
         [0019]    An apparatus constructed in accordance with the current invention alleviates these problems by the advantages found in its basic design. The ultimate expansion of the tubular is controlled because the expansion of the expanding bladder is controlled. The device incorporates a specially designed bladder that is designed such that it can contain pressure in excess of that needed to expand the tubular, and thus can even force the tubular to a more cylindrical shape than could be obtained with an explosive expansion, an uncontrolled hydraulic expansion or conventional indirect hydraulic expansion. The apparatus is also designed such that the expansion forces are almost entirely radial, such that unlike mechanical expansion methods, minimal axial or torsional forces are applied to the tubular being expanded. This means that long lengths of tubing can be inserted into a well or pipeline and subsequently expanded. The current invention allows the expansion of the end of the tubular without regard to the precise location of the apparatus with respect to the end of the tubing. As long as the cylindrical portion of apparatus designed in accordance with the current invention extends beyond the end of the tubular, it will be properly expanded. Each subsequent section of the tubular can then be expanded to the same repeatable final diameter. 
         [0020]    The present invention provides for an apparatus and for methods for expanding tubulars to a controlled diameter and for methods of fabrication of the apparatus. The expandable bladder of this invention is formed about a structural element that maintains its shape in the linear direction and allows for the introduction of pressurized fluid. In one preferred embodiment of the present invention, a bladder is formed over a removable shell which has been molded over a convoluted porous mandrel. The novel bladder of this invention is formed incorporating reinforcing wound or woven fibers that are encapsulated in resilient fluid resistant bladder material. 
         [0021]    After the bladder is formed, the removable shell is removed through the mandrel by one of several available methods, such as dissolution in a solvent, melting, etching with an acid or base, etc. The bladder is then placed against the mandrel via an internal vacuum or an external pressure on the bladder. The bladder is then overmolded with a resilient covering to form a primarily cylindrical outer shape while holding the bladder in a shrunken convoluted form. This apparatus is then inserted into the tubular section to be expanded. This invention can be used after the tubular is already in place in a borehole, pipeline or heat exchanger. Pressure is applied through the porous mandrel to expand the bladder against the inner wall of the tubular. As the pressure increases in a uniform radial manner, the wall of the tubular yields and it expands under the applied pressure. As the bladder expands, the convolutions of the bladder begin to straighten out. The resilient overmolded cover prevents the convolutions from folding over on themselves and damaging the reinforcing fibers in the bladder. As additional pressure is applied, the circumference of the bladder increases until it equals the arc length of the convoluted bladder. The yield strength of the bladder due to its construction is sufficient to support the pressure necessary to expand the tubular along with some additional overpressure which can be defined as additional pressure after the bladder has reached its full expansion. As additional pressure is applied to the bladder, the walls of the bladder contain the overpressure within the bladder. Consequently the bladder assumes a primarily cylindrical shape forcing the tubular to likewise assume a cylindrical shape despite variations in the material properties, or wall thickness of the tubular or external loads restraining the tubular. The pressure is then reduced and the bladder collapses to allow the apparatus to be withdrawn or moved to another section of the tubular to be expanded. 
         [0022]    An advantage of an apparatus made in accordance with this invention is that axial and torsional loads on the tubular sections expanded are greatly reduced or entirely eliminated. Axial loads generated by the internal pressure to the bladder are supported by either the internal mandrel or by the bladder itself so that minimal axial loads are applied to the tubular. This eliminates the possibility of collapsing or buckling the tubular. An additional advantage of the invention is that the apparatus resumes its original shape after each use due to the resiliency of the overmolded covering or, alternatively, a vacuum can be applied to the inlet of the mandrel drawing the bladder back into contact with the mandrel. The apparatus can thus generally expand a tubular to a diameter larger than that through which the tubular was inserted depending on the resistance of the surrounding material if in a well. The bladder is pressurized by either fluid pressure or gas pressure and the maximum extension of the bladder is controlled by its construction. Another advantage of the present invention is that while the apparatus can be made any reasonable length, the apparatus can expand tubulars that are either longer than the apparatus or shorter than the apparatus without a significant difference in the expanded diameter along the length of the tubular. 
         [0023]    Other aspects, features and advantages of the present invention will become apparent from the following detailed description of the various embodiments of the invention along with the accompanying drawings which illustrate the principles of the invention. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0024]    The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. 
           [0025]    It should be noted that the attached drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope. The invention may admit other equally effective embodiments. It should also be noted that most of the drawings show an apparatus that is relatively short axially. The length of the apparatus is only limited by handling, insertion, and fabrication restrictions. The shorter embodiments are shown for convenience and to show the internal configuration of the apparatus. 
           [0026]      FIG. 1A  is a partially sectioned isometric view of an apparatus made in accordance with the invention seated in a tubular section in its un-pressurized condition. 
           [0027]      FIG. 1B  is a partially sectioned isometric view of an apparatus made in accordance with the invention seated in a tubular section in its pressurized condition for expansion of a tubular section. 
           [0028]      FIGS. 2A-F  are a series of quarter section views of the inflatable bladder and overmolded resilient covering shown inside a tubular during the expansion cycle. 
           [0029]      FIG. 3A  is an isometric view of the center mandrel of the expansion device of the subject invention. 
           [0030]      FIG. 3B  is a partially sectioned isometric view of the mandrel of  FIG. 3A  covered by a removable shell. 
           [0031]      FIG. 3C  is a partially sectioned isometric view of the mandrel of  FIG. 3B  covered by a removable shell and resilient bladder material. 
           [0032]      FIG. 3D  is a partially sectioned isometric view of the mandrel of  FIG. 3C  in which the removable shell has been removed and the resilient bladder has been drawn in against the mandrel. 
           [0033]      FIG. 3E  is a partially sectioned isometric view of the mandrel of  FIG. 3D  in which the bladder has been over-molded with a resilient material. 
           [0034]      FIGS. 4A-C  are a series of sectioned isometric views depicting the fabrication of another preferred embodiment of the invention having a multilayer inflatable bladder. 
           [0035]      FIGS. 5A-F  are a series of sectioned isometric views depicting the fabrication of another preferred embodiment of the invention wherein the expansion device is fabricated about a removable porous tube. 
           [0036]      FIGS. 6A-D  are a series of sectioned isometric views depicting the fabrication of a preferred embodiment of the invention which consists of an inlet tube and end tube connected by a flexible member, a convoluted reinforced resilient bladder, and an overmolded resilient covering. 
           [0037]      FIGS. 7A-C  are a series of sectioned isometric views depicting the fabrication of a preferred embodiment of the invention which consists of a convoluted reinforced resilient bladder with axial reinforcement and an overmolded resilient covering. 
           [0038]      FIGS. 8A-B  are two sectioned isometric views depicting the fabrication of a preferred embodiment of the invention which consists of a convoluted mandrel and a resilient bladder wherein the convolutions in the mandrel and the bladder are matched to convolutions in the tubular to be expanded. 
           [0039]      FIG. 9  is a sectioned isometric view depicting the fabrication of a preferred embodiment of the invention which consists of a perforated center tube, a convoluted reinforced resilient bladder and an overmolded resilient covering configuration with a tube inside the perforated center tube which allows circulation of a either a heated or cooled fluid underneath the bladder. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0040]    The present invention relates devices and methods for controlled expansion of tubular sections. An expandable bladder of this invention is formed about a structural element that maintains its shape in the linear direction and allows for the introduction of a pressurized fluid. In one preferred embodiment of the present invention, a novel bladder is formed over a removable shell which has been molded over a convoluted porous mandrel which in this embodiment forms the structural element. The bladder of this invention is formed incorporating reinforcing wound or woven fibers that are encapsulated in resilient fluid resistant bladder material. The bladder is capable of withstanding internal hydraulic pressures sufficient to controllably force expansion of a surrounding metallic tube without rupture and damage. 
         [0041]      FIGS. 1A-B  provide isometric views of the present invention according to one preferred embodiment. The apparatus  100  is shown in  FIG. 1A  in an unexpanded condition inserted into tubular  200 . The tubular  200  could be part of a casing string oriented vertically or a liner being inserted horizontally as a patch in a pipeline or alternatively a tube being inserted into a tube sheet in a heat exchanger. The apparatus  100  is connected to a pressure source through connection  129 , and, in a typical well drilling operation, this pipe would lead to the surface. A convoluted bladder  140  surrounds the convoluted mandrel  120 . The bladder  140  is overmolded with a resilient coating  150  which holds bladder  140  in convoluted form until it is pressurized. Fluid (liquid or gas) is introduced into the mandrel  120  through connection  129 . This fluid is transmitted from the inside of the mandrel through perforations  124  which extend from the interior surface of the mandrel to the exterior surface of the mandrel. The fluid pressurizes the convoluted bladder  140  and radially expands the unexpanded section  202  of the tubular  200 . As the bladder expands, convolutions  144  straighten and become less pronounced. Resilient covering  150  stretches and compresses to essentially fill an annulus between the expanded bladder  140  and the expanded section of the tubular  203  as shown in  FIG. 1B  which provides a sectioned isometric view of the expanded tubular. 
       Use of the Expansion Device 
       [0042]      FIG. 2A  provides a finite element mesh of a cross section view of a quarter of the apparatus  100  and the unexpanded tubular  202 .  FIGS. 2B-F  show the expansion of the tubular and the contraction of the bladder upon depressurization. During the initial expansion, shown in  FIG. 2B , the pressure applied to the inside of the bladder  140  is transferred through the resilient coating  150  to the inner surface  205  of the unexpanded tubular  202 . As the tubular  202  plastically deforms, as shown in  FIG. 2C , the bladder  140  expands straightening out convolutions  144  and resilient coating  150  is both stretched circumferentially and compressed radially.  FIG. 2D  shows the bladder  140  at its maximum circumference. When the bladder  140  first reaches this maximum, the pressure on the inner surface  145  of the bladder  140  and the pressure on the outer surface  157  of the resilient covering  150  are essentially the same (except for the pressure required to expand the resilient covering  150  which is small). Consequently the roundness of the deformed tubular  202  can be altered by any variation in the material properties of the tubular  202  and by any external loads applied to the tubular. When additional pressure is applied to the inner surface  145  of the bladder  140  (through connection  129 ) the additional load is carried by the bladder  140  as a circumferential tension. This tension T is given by T=(P inner −P outer )*R local  where P inner  is the internal pressure on the bladder  140 , P outer  is the pressure on the outer surface of the bladder, or equivalently the pressure on the outer surface of the resilient covering, and R local  is the local radius of curvature of the bladder  140 . Initially if the tubular  202  is not round, R local  will vary and any pressure difference must be supported by bending moments in the tubular. Since the tubular is already in fully plastic strain at this point, the additional bending moments it can support are limited. Thus, as the internal pressure is increased and the tension T in the bladder increases, both the bladder  140  and the tubular  202  are forced to an essentially cylindrical shape. As the pressure is released the bladder returns to its initial configuration as shown in  FIGS. 2E and 2F . The tubular will recover any elastic strain from the expansion process and will try to return to its non-cylindrical shape but since its recovery is limited to roughly 0.5% strain, any non-uniformity of radius will be limited. 
         [0043]    If the tubular is being expanded inside another tubular such as is the case for repairing casing or repairing a pipeline, the inner tubular will first conform to any anomalies in the outer tubing and then as additional pressure is applied, both tubulars will expand until the bladder reaches its fully expanded circumference. Any additional overpressure will tend to force both the bladder and the two tubulars into a more cylindrical shape which will be retained upon depressurization. 
       Fabrication of the Tubular Section Expansion Device 
       [0044]    In one preferred embodiment of the invention the expansion device  100  is formed around a mandrel  120  having a series of convolutions  122  which are sized to conform to the size of the interior surface of the bladder  140  in the deflated condition. The arc length of the convolutions is sized to conform to the circumference of the inner surface of the bladder in the expanded condition. One end of the mandrel  128  is closed off and the other end  129  is open. As shown in  FIG. 3A  the mandrel  120  contains a series of holes  124  through the wall of the mandrel. These holes provide fluid communication between the inside and outside of the mandrel. This function could as well be performed by a mandrel which provides a region with porous walls rather than discrete holes in a solid wall. 
         [0045]      FIG. 3B  shows the next step in the fabrication of this particular embodiment of the invention. The mandrel  120  is coated with a removable shell  130 . This shell can be formed from a low-melting point metal such as Woods metal (a lead alloy), a metal such as zinc which can be etched with an acid or a base, a hard wax, a low melting point plastic, a dissolvable plastic or any similar material which will allow the bladder to be formed over it and can then be subsequently removed from between the mandrel and the bladder by either heating the assembly to liquefy the shell material or by dissolving the shell in a solvent, or by etching the shell with an acid or a base. This removable shell  130  is formed to the dimensions of the internal surface of the bladder  140  when the bladder is fully expanded but is not subjected to any overpressure as described above. Said shell  130  can be formed to the final configuration in a mold or can be molded to a larger diameter than required and machined to the final required shape. 
         [0046]    The next step in fabricating said embodiment of the invention is forming the bladder  140  over the removable shell  130  as shown in  FIG. 3C . The bladder is a composite structure formed from woven or wound fibers in a substantially fluid impervious resilient matrix. The fibers can be metallic such as steel, stainless steel, titanium, or any other suitable metal or can be formed from a polymer fiber such as Aramid, PEN, polyester, or similar high strength fiber or can preferably be formed from carbon fiber. The reinforcing fibers may be treated with a coating such as a silane or otherwise be treated to improve their adhesion to the resilient matrix. The resilient matrix can be formed from an elastomer such as Buna-N rubber, polyurethane, fluorosilicone, or fluorocarbon. A particularly preferred material for use in the fabrication of the bladder is a silicone rubber due to its flexibility, adhesion, and temperature range. If desired, the bladder may be a laminated structure with an inner layer of a fluid resistant polymer, for example polyamideimide or PET. 
         [0047]    In said preferred embodiment of the invention, the majority of the fibers are oriented in alternating layers of helixes wherein the angle between the longitudinal axis of the bladder and the fiber direction is between 40° and 80° but is preferably greater than 55° such that the bladder does not expand beyond its fully inflated condition except due to the elastic stretching of the reinforcing fibers. These fibers typically have a high elastic modulus and an elastic strain in the range of 0.5% to 3%. 
         [0048]    Following the formation of the bladder  140 , the removable shell  130  is removed by one of a variety of methods depending on the material from which the removable shell was formed. For example, the removable shell could be formed from a metal alloy having a low melting temperature. When the mandrel  120 , removable shell  130  and bladder  140  are heated above the melting temperature of the metal alloy, the shell  130  liquefies and can be removed through the perforations  124  of the mandrel  120  and then through connection  129 . Alternatively the removable shell  130  can be formed from a dissolvable material such as polystyrene which can then be subsequently removed with a suitable solvent such as acetone through said perforations  124  in mandrel  120 . Any suitable material which can be used to form the composite bladder  140  and can then subsequently be removed through the perforations  124  of the mandrel  120  without damaging either said bladder or said mandrel may be used. 
         [0049]    Following the removal of said shell  130  the bladder  140  is placed in contact with mandrel  120  as is shown in  FIG. 3D . This is accomplished either by internal vacuum applied through connection  129  and through perforations  124  or by applying external pressure to the bladder. A resilient covering  150  is then overmolded onto the bladder as diagrammed in  FIG. 3E . The resilient covering  150  can be made of any elastomer which will tolerate the conditions to which the apparatus will be subjected during the expansion of the tubular  200 . Said material may be polyurethane, silicone, fluorosilicone, fluorocarbon, or similar material. The overmolded resilient covering  150  holds the bladder  140  in its substantially convoluted form when not under internal pressure. As pressure is applied, the bladder  140  will expand compressing the overmolded resilient covering  150  radially and stretching it circumferentially. After the tubular  200  is expanded, and the pressure is released; the overmolded resilient covering  150  returns to its unstressed state causing the bladder  140  to resume its convoluted form. This process is shown in  FIG. 3 . 
       ALTERNATE EMBODIMENT 
       [0050]      FIGS. 4A-C  shows an alternative preferred embodiment of the invention. The convoluted mandrel  120  and the removable shell  130  are formed in the same manner as outlined above. In the previous embodiment, the reinforcing fibers of the bladder were completely surrounded by a resilient covering. In that embodiment the surrounding matrix must be resilient in order for the formed bladder  140  to be convoluted without overstressing the fibers. The fiber stress due to the bending is relieved by allowing the fibers to move relative to one another through the thickness of the bladder. The present preferred embodiment uses a number of layers  170  to fabricate the bladder. Each bladder layer  170  is reinforced with fibers of metal, polymer or carbon in the same manner as described earlier. In the present embodiment, however, the matrix in which the fibers are imbedded need not be resilient if the bladder layers  170  are thin enough. The convolutions  124  must be designed with respect to the thickness of the bladder layers  170  such that conforming the bladder layers to the convolutions of the mandrel would not cause the stresses in either the non-resilient matrix or the reinforcing fibers to exceed their elastic limit. Ideally the moment required to form each bladder layer into the convoluted configuration should be smaller than the restraining force of the overmolded resilient covering  150  when the bladder is not pressurized. Each bladder layer  170  would be separated from its adjacent bladder layer with a thin intermediate layer to prevent adhesion of each successive layer to its underlying layer. This intermediate layer could be a layer of polymer such as polytetrafluoroethylene, a layer of wax, a layer of mold release agent such a polyvinyl alcohol, a layer of powder such as graphite or boron nitride, or any similar agent which will allow the adjacent bladder layers to slide with respect to each other.  FIGS. 4A-C  show five bladder layers  170  in the bladder but any number of bladder layers could be used to achieve the required conformability along with the required strength.  FIG. 4C  shows the overmolded resilient covering over the outermost layer of the bladder. The layered bladder  170  will be brought into contact with the convoluted mandrel  140  by either internal vacuum or, more preferably, external pressure, and the resilient covering  150  will then be molded over the layered bladder  170 . Preferably the overmolded resilient covering  150  will be bonded to the outermost layer of the bladder. 
         [0051]      FIGS. 5A-F  show another preferred embodiment of the invention.  FIG. 5A  shows the mandrel assembly wherein a removable convoluted mandrel  190  is assembled onto a perforated tube  180 . The mandrel and the perforated tube will be made from different materials because the mandrel will eventually be removed while the perforated tube will remain to provide fluid connection to the apparatus and to support the axial loads imposed by the pressure. The mandrel  190  is coated with a removable shell  130  as shown in  FIG. 5B . As in the previous embodiments this shell can be formed from a low-melting point metal such as Woods metal, a metal such as zinc which can be etched with an acid or a base, a hard wax, a low melting point plastic, a dissolvable plastic or any similar material which will allow the bladder to be formed over it and can then subsequently be removed from between the mandrel and the bladder by either heating the assembly to liquefy the shell material or by dissolving the shell in a solvent, or by etching the shell with an acid or a base. The shell must be removed in such a manner that the removable mandrel remains in place to allow controlled convolution of the bladder. This can be accomplished by using a different process to remove the shell  130  than will be used to remove the removable mandrel  190 . For instance the shell could be removed by melting while the mandrel is removed by etching. An example of this process would be forming the center tube from 304 stainless steel, forming the mandrel from mild steel, and forming the shell from a low melting point zinc alloy. In this example the shell would be removed through the perforated mandrel by melting the shell. After convoluting the bladder  140  and overmolding the bladder cover  150 , the mandrel  190  can be etched out through the center tube  180  using a hydrochloric acid solution. In this case the bladder would be formed from an elastomer which is inert to hydrochloric acid. The process could also utilize two materials with different melting points such as forming the mandrel from a fusible alloy and forming the shell from a hard wax. The wax could be removed after forming the bladder by heating the apparatus to a moderate temperature which would melt the wax but not melt the mandrel. After the bladder  140  is convoluted and the bladder cover  150  is overmolded onto the bladder, the mandrel  190  would then be removed by heating the apparatus to a higher temperature sufficient to melt the removable mandrel  190  but still low enough not to damage the bladder  140  or the overmolded bladder cover  150 . Any combination of materials for the mandrel  190  and the shell  130  would be suitable if they allow layup of the bladder  140  in expanded form followed by removal of the shell  130 , convolution of the bladder  140 , overmolding of the resilient bladder cover  150 , and finally removal of the mandrel  140 . 
         [0052]    Removal of the mandrel  190  allows the bladder  140  to be collapsed and inserted into a tubular through an entrance that is smaller than the tubular to be expanded. The bladder  140  can then be inflated and used to expand the tubular. The bladder assembly can subsequently be collapsed again and then be removed through the smaller opening. This process could be especially beneficial in certain heat exchanger repairs or in situations where oilfield casing is partially collapsed prior to expansion. 
         [0053]    In another preferred embodiment of the present invention the axial load is supported by a flexible member such as a cable. The flexible member  184  is connected to both the inlet tube  182  and the end tube  186  with spider assemblies  188  as shown in  FIG. 6A-D . A removable convoluted mandrel  190  surrounds the inlet tube, flexible member, and end tube. A removable shell  130  is molded over the removable mandrel  190 . The bladder  140  is laid up as described above and the shell  130  is removed through the mandrel  190  and the inlet tube  182  by any one of the methods described previously. The bladder  140  is then convoluted around the mandrel  190  and the bladder cover  150  is overmolded onto the bladder  140 . The mandrel  190  is then removed by one of the methods described previously. The bladder  140  can be further collapsed if necessary during installation and since the bladder  140  is flexible in its unexpanded configuration as is the flexible member  184 , the apparatus can thereby be inserted in a tubular that has a bend such as a multipass heat exchanger. 
         [0054]    In an additional preferred embodiment of the present invention the axial load is supported by axial fibers in the bladder itself. In this embodiment, shown in  FIGS. 7A-C , the mandrel  250  would be initially fabricated with an inlet tube  256  and either an outlet tube or, as shown in  FIG. 7A , a closed end  254 . The shell  260  would be overmolded onto the mandrel  250 . The bladder  270  would be laid up onto the shell as described previously but in addition to the helically oriented reinforcement fibers, longitudinally oriented reinforcement fibers would be formed into bladder  270 . The required number of the longitudinal fibers would be determined by the axial load to be carried during pressurization less the axial load carried by the helically oriented fibers. As shown in  FIG. 7B , following layup of the axially reinforced bladder  270 , the shell  260  would be removed and the bladder  270  would be convoluted against the mandrel  250 . A bladder cover  280  would be overmolded onto the bladder  270  as described previously.  FIG. 7C  shows the apparatus after removal of the mandrel  250  by any of the methods described earlier. Remaining would be the axially reinforced bladder assembly consisting of the axially and helically reinforced resilient bladder  270  and the bladder cover  280 . An inlet tube  182  is inserted into the open end of the bladder assembly and is sealed to the bladder  270  by clamping and sealing methods known in the industry. If a second open end is provided rather than the closed end shown in  FIG. 7A , an end tube is inserted into the second end of the bladder  270  and sealed in a similar manner to the inlet tube. This embodiment would provide a more flexible apparatus which could be inserted into tubulars with restricted access. 
         [0055]      FIGS. 8A-B  show an additional preferred embodiment of the invention wherein the tubular to be expanded  330  is convoluted. In this embodiment the convoluted mandrel  120  is constructed such that the convolutions  122  of the mandrel  120  correspond one to one to the convolutions  332  of the tubular  330  to be expanded having the same number of convolutes and having the proper amplitude such that the bladder  140  will substantially pressurize the convoluted tubular  330  uniformly during expansion. In this embodiment the fabrication of the bladder assembly is essentially the same as demonstrated in  FIGS. 3A-D , wherein the removable shell  130  will be formed over said mandrel  120  to the dimensions of the bladder in its expanded form and the bladder  140  will be laid up over the shell  130  wherein the bladder has reinforcing fibers in a resilient matrix. The matrix may be fully cured or only partially cured at this point. The removable shell  130  is removed by any of the methods described previously. If the bladder  140  has been fully cured prior to removal of the shell, the bladder  140  must be convoluted against the convoluted mandrel  120  by applying a vacuum to the underside of the bladder  140  through the mandrel  120 . This vacuum would be held during insertion of the apparatus into the convoluted tubular  330  to be expanded. After expansion of the tubular, a vacuum would once again be applied to the bladder  140  to allow movement of the apparatus into another section of convoluted tubular  330  to be expanded or to allow removal of the apparatus. 
         [0056]    Alternatively, if the resilient matrix is only partially cured prior to removal of the shell  130 , the bladder  140  can be convoluted against the mandrel  120  by either internal vacuum or external pressure, and the resilient matrix can be further cured in this configuration allowing the apparatus to be inserted, moved and removed without having to maintain a vacuum on the apparatus. 
         [0057]    A further preferred embodiment of the present invention is shown in  FIG. 9 . The center tube  320  contains an inner tube  310  having an inlet  316  that provides fluid communication directly to the distal end  322  of the center tube, through the holes  321  in the distal end of the center tube  320  and into the plenum  145  between the center tube  320  and the bladder  140 . A spider arrangement  312  and a centering flange  314  align the inner tube  310  with the center tube  320 . The fluid must then flow between the bladder and the center tube and exits through the holes  324  in the center tube at the inlet end of the apparatus and into the annulus  326  between the center tube and the inner tube. The inlet path for the fluid would not matter for a normal expansion, but this configuration allows for a flow of fluid along the inner surface of the bladder in the annulus  145 . If the fluid is hotter or colder than the tubular to be expanded, this allows heat transfer to or from the tubular. 
         [0058]    Two scenarios are envisioned where this could be of value. In order to seal the expanded tubular to the tubular that is being repaired, often an epoxy coating is applied to the exterior of the tubing to be expanded such that the epoxy coating will form a seal between the tubular being expanded and the tubular that is being repaired. Once the two tubulars are brought into contact by the expansion of the inner tubular, a warm fluid can be circulated through the apparatus heating the inner tubular and the epoxy coating and thus accelerating the curing of the seal. 
         [0059]    Another aspect of this embodiment involves the circulation of cold fluid through the bladder during the expansion process. This cools the tubular to be expanded. The cooled tubular is expanded inside the tubular to be repaired and slightly expands the tubular being repaired. When the bladder is depressurized, both tubulars elastically recover. Since the inner tubular is cooler than the outer tubular, the inner tubular will expand as it comes into thermal equilibrium with the outer tubular increasing the contact between the inner tubular and the outer tubular. 
         [0060]    A further advantage of the present invention is the ability to use the expansion device to insert the tubular to be expanded. This process is especially applicable to the insertion of a casing string into a wellbore. The lengths of casing can be assembled in the normal manner and welded together at the surface. When the required length of casing string is completed, the expansion apparatus can be inserted into the top end of the casing string and pressurized to a pressure adequate to support the casing string due to the frictional force between the bladder and the inside surface of the casing but at a pressure less than that needed to expand the casing. For example a 1000 foot string of 18 inch diameter 0.5 inch wall casing weighs approximately 97,000 pounds but the friction on the surface of a 10 foot long expansion device pressurized to 1000 psi would support 680,000 pounds based upon a friction coefficient of 0.1 and the wall stresses in the bladder would be only 10% of the stresses supported during the expansion of the casing. After the casing string is lowered to the proper depth, the expansion apparatus can be further pressurized to expand the top of the casing against the existing casing string, locking it into place. The expansion apparatus can then be depressurized and lowered into the unexpanded section of the casing. Each successive section of casing can then be expanded until the full length of the casing string has been expanded after which the expansion apparatus can be withdrawn and returned to the surface. 
         [0061]    While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.