Abstract:
A skin and a method for restructuring the inner surface of a tube of long length includes manufacturing a skin, in a material with expansion rate greater than 50%, the external surface of which includes a restructuring print determined in order to take into account the longitudinal and radial expansions that the skin is going to undergo, and as a function of the desired final surface state for the tube to be restructured, longitudinally expanding the skin up to the required length for the tube, longitudinally introducing expanded skin inside tube to be restructured, and radially expanding the skin to realize the restructuring.

Description:
SUMMARY OF THE INVENTION TECHNICAL CONTENT 
       [0001]    The invention concerns a method for restructuring the inner surface ( 3 ) of a long length tube ( 2 ) that comprises the steps of
       Manufacturing a restructuring skin ( 1 ) in a material with an expansion rate greater than 50%,   Longitudinally expanding the skin up to the length required for the tube;   Introducing longitudinally expanded skin ( 1 ′) inside tube ( 2 ) to be restructured   Radially expanding skin ( 1 ″) to do the restructuring.
 
The invention also concerns a longitudinally expandable skin for restructuring the surface of a tube inner lining forming a duct for gas or fluid transport.
       
 
         [0006]    1. Technical Domain of the Invention 
         [0007]    The invention concerns the restructuring of a tube inner lining surface, notably of a pipeline constituting a duct for gas or fluid transport, by means of restructuring skins. 
         [0008]    2. Anterior Art 
         [0009]    In the following description the meaning of “restructuring a surface” is
       the ultra smoothing of a surface having the property to reduce the aerodynamic drag of a wall with regards to a rough surface,   structuring a surface: conventional structured surfaces are presented with groove shapes aligned in the direction of the flow. Their property, among others, is to reduce, with regards to a smooth surface, the aerodynamic drag along a wall. This property results from an attenuation, in the direction transverse to the flow, of speed fluctuations and, therefore, of the corresponding turbulence component.       
 
         [0012]    The structured surfaces can be bi-dimensional or tri-dimensional. 
         [0013]    Bi-dimensional structures present a constant height in the flow direction, their dimensions only varying in the transverse direction. The bi-dimensional structures of the anterior art (usually called “riblets”: “small rib”) can present some a—triangular, b—semi circular, c—trapezoidal, and d—knife blade shapes. 
         [0014]    The tri-dimensional surfaces may be represented, i.e. by segments of disks in the flow direction (Bechert, 1987), shapes obeying a fractal distribution (U.S. Pat. No. 4,650,138 and U.S. Pat. No. 4,759,516) or herringbone structures (EP 0 543 647 A1). 
         [0015]    “Restructuring skin” is meant as an elastic balloon (an enclosed wall) or membrane (an open wall), increasing in volume under the effect of pressure, and capable to line the shape of the object to be restructured. 
         [0016]    The objective of the restructuring surface is to modify the surface state, in order to obtain,
       either ultra-smooth surfaces;   or structured surfaces.       
 
         [0019]    The surface state modification provides a reduction in load loss, advantageous in the case of tube inner linings forming a gas or fluid duct. The ultra-smoothness, on the other hand, allows for reducing friction coefficient, salts and paraffin deposit in production tubes, the number of interstices and holes resulting from a material deposit with insufficient material thickness. 
         [0020]    Patent FR 2.879.948 describes a device and method for realizing restructured surfaces in ducts, in order to reduce the aerodynamic drag by means of a restructuring skin whose external surface is smooth or include patternings. 
         [0021]    A means was sought-after to apply a skin for restructuring an inner lining surface in large size tubes constituting a duct, i.e. for gas or fluid transport, in order to reduce load losses within said duct. However manufacturing such membranes for placement of restructuring skins into tube inner linings pose many problems due to their sometimes complex shape (namely in case of double-cone skins), but also to their large size, and to the restructuring indentation that must conform to the structured or ultra smooth surface state required for the lining. Indeed, in case of, i.e. gas transport tubes, they are about 12 m long, therefore
       manufacturing a very long skin requires complex and very expensive tooling, notably with regard to mould size;   in order to have a beam mounted cantilever to support a very long skin requires a complex (stepped diameter), voluminous, heavy beam shape counterbalanced with a weight of momentum equivalent to that exerted by the beam.       
 
       DESCRIPTION OF THE INVENTION 
       [0024]    This invention proposes to apply a longitudinally expandable skin for restructuring the inner lining surface in large size tubes. 
       SUMMARY 
       [0025]    The invention concerns a method for restructuring the inner surface ( 3 ) of a tube ( 2 ) of long length that comprises the steps of
       manufacturing a restructuring skin ( 1 ) in a material with an expansion rate greater than 50%,   longitudinally expanding the skin up to the required length for the tube;   introducing longitudinally expanded skin ( 1 ′) inside tube ( 2 ) to be restructured   radially expanding skin ( 1 ″) to do the restructuring.       
 
         [0030]    Preferably, the radial expansion is provided by putting the skin under pressure. 
         [0031]    The skin withdrawal and skinning can done by reducing the pressure. 
         [0032]    The skin withdrawal and skinning can done by decreasing the radial expansion. 
         [0033]    Preferably, the rate of expansion of the skin material is greater than 100%, in a more preferred way 300%, and in an even more preferred way greater than 600%. 
         [0034]    In one form of embodiment, an inner lining is introduced inside the tube before introducing the skin. 
         [0035]    Advantageously, the state of the skin surface before expansion is defined as a function of the longitudinal and radial expansions that will be exerted on the skin, and of the required surface state of the skin after expansion. In one form of embodiment, the required surface state is ultra smooth. In another form of embodiment, the required surface state is a bi- or tri-dimensionally structured surface state. 
         [0036]    Preferably, the tube forms a duct for gas or fluid transport. 
         [0037]    The invention also concerns a longitudinally expandable skin for restructuring the surface of a tube inner lining forming a duct for gas or fluid transport. Preferably, the skin material has a rate of expansion greater than 50%. 
         [0038]    Advantageously, the skin material is silicone-based. 
         [0039]    In one form of embodiment, the skin external surface presents a state of ultra-smooth surface. 
         [0040]    In another form of embodiment, the skin external surface presents a bi- or tri-dimensionally structured surface state. 
     
    
     
       DETAILED DESCRIPTION OF THE INVENTION 
         [0041]      FIGS. 1   a ,  1   b ,  1   c ,  1   d ,  1   e  represent several steps of the inner lining restructuring method of a tube by means of an expandable restructuring skin according to the invention. 
           [0042]      FIG. 1   a : Cross-section view of the restructuring skin before longitudinal expansion and internal pressurization (initial state  1 ). 
           [0043]      FIG. 1   b : Cross-section view of the restructuring skin expanded longitudinally (longitudinally expanded state  1 ′). 
           [0044]      FIG. 1   c : Cross-section view of a tube during the application of an inner lining (deposit by spray, injection, chalking, dip coating . . . ). 
           [0045]      FIG. 1   d : Cross-section view of the tube to be internally restructured, equipped with the longitudinally expanded skin according to the invention. 
           [0046]      FIG. 1   e : Cross-section view of the tube equipped with the skin inflated and under pressure (longitudinally expanded, radially expanded, and pressurized state  1 ″). 
       
    
    
     DESCRIPTION OF THE FIGURES 
       [0047]      FIGS. 1   a  to  1   e  describe, in a non restrictive manner, a method of restructuring an inner lining surface of large size tubes by means of a restructuring skin according to the invention that consists of the following steps:
       a) Manufacturing a restructuring skin ( 1 ) which surface state is, in the initial state, defined according to the longitudinal expansion that will be exerted on the skin, and the required final surface state of the longitudinally expanded skin ( FIG. 1   a ). The manufacture is done using any means known of the skilled man, i.e. in a mould for silicone skin, and by stripping using various processes, such as: lubricant, lost-wax, disassembling mold made of several parts.   b) Longitudinal expansion of the skin according to the required restructuring length of the tube: expanded skin ( 1 ′) ( FIG. 1   b ).   c) Possible introduction of a cold-dropped lining ( 3 ) in the tube to be restructured ( 2 ): epoxydic bases with solvent (phenolic), in aqueous phase, or without solvent, polyurethane bases, PVC, or hot-dropped: Polyamide, epoxy, or PVC, inside the tube, if the tube is not already lined with a structurable internal lining ( FIG. 1   c ).   d) Setting the skin ( 1 ′) inside the tube to be restructured and attaching centering supports ( 4 ) externally to the tube ( FIG. 1   d ).   e) Inflating and putting the skin under pressure by means of a valve ( 5 ) or radial expansion by any other means known of the skilled man, in order to realize the step of restructuring of the inner lining ( FIG. 1   e ): longitudinally extended and radially expanded skin ( 1 ″).   f) Deflating, or withdrawing and skinning of the skin by successive and/or simultaneous actions of pressure reduction and axial expansion.   g) Dissociating the external supports and withdrawal of the skin.         
         [0055]    The means of radial expansion may be i.e. brought on a shaft, which longitudinal displacement along the tube main axis permits the application of the extended skin over the whole length of the tube. The means of radial expansion may be a toric form elastic assembly in order to possibly apply a more regular pressure over an inner circumference of the duct, i.e. a ring-shaped chamber, pressurized or in a flexible material, that is displaced by sliding along the inner surface of the skin. A set of cushions, or wheels, arranged in a circumference, and including means of applying a radial pressure force, either mechanical or pneumatic, onto the skin, may also be considered. Any other means known of the skilled man may also be appropriate. 
         [0056]    The material constituting the skin may be any product or material with good replica properties, a low adhesion, and a strong rate of expansion. A strong rate of expansion means a rate of expansion of about 50%; preferably of about 100%, very preferably of about 300%; and even more preferably of about 600%. 
         [0057]    As examples of products that may be used for the skin membrane, notably elastomers with a strong rate of expansion may be mentioned, such as rubber, silicones, or KRATON™ type of materials, alone or in mixture. 
         [0058]    Some silicones have a rate of expansion greater than 600%. The preferred material for the skin is silicone-based. 
         [0059]    The skin membrane may include reinforcement materials to provide improved membrane resistance during longitudinal extension. 
         [0060]    The method according to the invention may be used for restructuring inner tubes including cold-dropped liners, such as: epoxydic bases with solvent (phenolic), in aqueous phase, or without solvent, polyurethane bases, PVC. 
         [0061]    The method according to the invention may also be used for restructuring hot-dropped linings, such as polyamide, epoxy or PVC types. 
         [0062]    This membrane presents appreciably the same roughness at that of the mold considering a replica capacity (wetability) of material in liquid phase greater than the mould roughness fineness (deformation height). 
         [0063]    The mould is made with a surface state (lower roughness height) greater than that of the inner linings applied in a conventional way. The surface state is chosen at the upper limit of the sensitivity threshold of the friction factor. 
         [0000]    So the roughness:
       of an inner lining conventionally applied is in the order of 10 to 20 μm (average of 5 samples of the surface distortion peak to peak interval: Ry5)   of a primary mold (glass, broken in steel . . . ) is in the order of 1 μm (Ry5)   of the replica membrane surface (secondary mold) is in the order of 1 μm (Ry5)   of the lining surface (tertiary mold) replicated by the membrane is much less than that of the membrane (secondary mold)   sensitivity threshold of the friction factor in the order of 1 μm.       
 
       ADVANTAGES OF THE INVENTION 
       [0069]    The interest of the method is to permit an easy installation of skins for restructuring inner lining surfaces of long length tubes, while maintaining a very good surface state. Indeed, in addition to simplifying by using a skin size smaller than that of the tube which contain the lining to restructure, skin withdrawal is also facilitated
       Membrane skinning is facilitated by a high longitudinal tension (high axial force).   Membrane skinning is facilitated by the alternated actions on membrane depressurization and axial expansion reduction.
 
From another point of view, the method according to the invention provides high quality surface states for the inner lining.
       
 
         [0072]    Indeed, the longitudinal and radial expansions produce a decrease in height of the surface protrusions (roughness) appreciably proportional to the product of longitudinal and radial expansion rates. 
         [0073]    Similarly, the longitudinal and radial expansions produce a distance increase between the protrusions appreciably proportional to the product of longitudinal and radial expansion rates. 
         [0000]    With regard to roughness:
       physical roughness (measured by roughness tester) is decreased appreciably in proportion to the product of longitudinal and radial expansion rates;   hydraulic roughness (measured by friction factor) is decreased appreciably in proportion to the product of longitudinal and radial expansion rates;