Abstract:
A method for heating a zone of an elongate tubular article. A heat resistant, heat transmitting and heat dispersive shroud material is applied to the zone and a hot gas source is applied to the outside of the shroud material to cause heat to be transmitted through the shroud material to the zone.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to a method and apparatus for heating a zone of an elongate tubular article, for example a zone of the surface of a pipeline in the course of applying a sleeve or patch on coated pipes, employing a hot gas source, such as a heater device that provides a heated air stream, or when using a flame, such as a torch flame to heat the pipe.  
           [0002]    Heating may, for example, be employed for heating a pipeline weld joint and the adjacent coating in the field to a temperature suitable for subsequent installation of a covering. In particular, the present method and apparatus are especially useful where the temperature to which the line coating must be heated exceeds its melting point, and the covering is to be applied is a heat shrinkable sleeve, tape or patch coated with a hot melt adhesive whose adhesive requires the substrate to be heated to a temperature close to or above the melting point of the substrate. More particularly, the method is especially advantageous when the coating on the pipeline is polypropylene, and the hot melt adhesive on the sleeve, tape or patch requires the substrate to be at least 160° C. in order to achieve an acceptable bond.  
         BRIEF SUMMARY OF THE INVENTION  
         [0003]    In the present invention, a heat resistant, heat transmitting and heat dispersive shroud material is applied on a zone of the surface of the pipeline or other elongate tubular article to be heated, and a hot gas source is applied to the outside of the shroud material to cause heat to be transmitted through the shroud material to said zone.  
           [0004]    The function of the shroud material is to protect the pipeline coating from direct exposure to the combustion product of the flame, while effectively transferring the heat from the flame to the pipeline coating. In the absence of the shroud material, the extreme temperature of the flame or hot gas has been found to degrade the pipeline coating. For example, if the pipeline coating is polypropylene, it causes the surface to become “waxy” due to degradation of the polymer and/or blooming to the surface of lower molecular weight polymer and additives. Such a surface is very difficult to bond to.  
           [0005]    Further, the shroud material serves to reduce the rate of heat transfer through the pipeline coating to the steel pipe, as compared with the rate of heat transfer that would occur if the hot gas source were played directly on the pipeline coating. Such reduction in the rate of heat transfer may for example be achieved by virtue of the fact that the shroud material may be heat insulative, so that a temperature gradient exists between the outer and the inner sides of the shroud material. Secondly, or alternatively, the shroud material may be heat dispersive, that is to say it disperses hot gases transversely over its outer side when a source of hot gas is played on the outer side of the shroud material.  
           [0006]    By reducing the rate of heat transfer through the pipeline coating, the advantage may be achieved that, with adhesively bonded thermoplastic coatings, the reduction in heat transfer may reduce or eliminate total melting of the coating and adhesive and consequent dimensional instability of the coating and/or adhesive.  
           [0007]    While the method of the present invention is particularly advantageous when used in the installation of field coating over pipelines covered with thermoplastic coatings, it may be used advantageously for pipes coated with any material which does not stand up well upon direct exposure to a flame, and with any field-applied coating system which requires substrate temperatures high enough to imperil the integrity of the pipe coating.  
           [0008]    The shroud material should be heat resistant, so that it does not melt, burn, distort or decompose when the hot gases or flame is played on it.  
           [0009]    The shroud material is preferably designed to transmit heat at an optimum rate to the pipeline coating. If it is too insulating, the heating rate will be unacceptably low. If it is too conductive, or if it has openings that allow the hot gases to pass through, it will not protect the pipeline coating against degradation. Examples of suitable materials include non-burning, continuous pervious woven or non-woven blanket materials, for example non-metallic woven blanket materials, metallic mesh materials, and heat conductive sheet materials for example metal strip material which may, for example, be backed with an insulative liner, which may also serve as a release coating, for example of polytetrafluoroethylene (TEFLON trade-mark). One skilled in the art of pipeline coatings can readily determine by routine experimentation whether a given material is suitable for use as a shroud material in accordance with the invention.  
           [0010]    Desirably, the shroud material is flexible, so that it can be wrapped around or will conform closely to the curvature of the pipeline or other tubular article. One particularly preferred material is woven glass fibre mat, for example two thicknesses of the woven glass fibre material sold by Amatek Inc., Wilmington, Del., under the trade-mark SILTEMP P4CSR.  
           [0011]    In one particularly preferred form of the present invention, the shroud material is used together with heat shield structures comprising two heat resistant flanges spaced apart, for example axially of the tubular article, and having the covering material disposed between the flanges, so that the heat is trapped and is more efficiently channelled to the exposed surface of the shroud material.  
           [0012]    In the preferred form, for heating a pipeline weld joint and the adjacent coating for subsequent installation of a covering, two heat shield structures are used. At each end of the weld joint, shroud material is wrapped, the shroud material being wider than the width of the region of the pipeline coating to be heated. A heat shield structure providing an inner and an outer flange is installed over the pipeline coating adjoining the uncoated steel weld joint at each end of the weld joint. Heating, preferably by direct flame, is than trained on the region between the two inner most flanges to heat the uncoated steel to the temperature necessary to achieve a good bond to the adhesive on the field joint covering. Heating is then applied, preferably using direct flame, to the regions between the inner and outer flanges, to heat the pipeline coating to a temperature above the minimum at which a bond can be established with the adhesive on the field joint covering. The flame is trained on the non-burning shroud material and the heat penetrates through it to the underlying coating.  
           [0013]    The heat shields are then removed, and the field joint covering is installed before the weld joint and the adjacent coating can cool to a temperature below which a bond to the field joint covering can be achieved.  
           [0014]    In the preferred form, each heat shield structure consists of an inner split metal flange and an outer split metal flange that are connected together to create a confined space somewhat wider than the width of the portion of the pipeline coating to be heated. The outer flange preferably has a cylindrical axially outward extension to protect the pipeline coating, to assist in securing the shroud material, and to assist in achieving and maintaining alignment with the pipe. 
       
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0015]    The invention will now be described in more detail, by way of example only, with reference to the accompanying drawings.  
         [0016]    [0016]FIG. 1 is a partially schematic side view, partially in section, showing a pipe joint together with one form of apparatus in accordance with the invention.  
         [0017]    [0017]FIG. 2 is a fragmentary plan view of a shroud material employed in the method and apparatus of the present invention.  
         [0018]    [0018]FIG. 3 is a longitudinal cross section through the joined ends of the shroud material of FIG. 2, taken on the line  3 - 3  in FIG. 5.  
         [0019]    [0019]FIG. 4 is a partially schematic perspective view showing a method of joining the ends of the shroud material.  
         [0020]    [0020]FIG. 5 is a partially schematic perspective view showing the pipe joint together with an apparatus of the invention.  
         [0021]    [0021]FIG. 6 is a partially schematic cross section showing a further form of apparatus in accordance with the invention.  
         [0022]    [0022]FIG. 7 is a plan view of the apparatus of FIG. 6. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0023]    Referring to the drawings, FIG. 1 shows by way of example pipe sections  11  and  12  welded together at a weld joint  13 .  
         [0024]    Outwardly from the joint  13 , each pipe section  11  and  12  has a polyolefin, for example polypropylene, pipe coating  14  and  16  thereon.  
         [0025]    It may be desired to install a heat shrinkable sleeve covering the portions of metal of the pipe sections  11  and  12  adjacent the weld joint  13  that are free of the coatings  14  and  16 , such sleeve being connected to the coatings  14  and  16 . Such heat shrinkable sleeve may be, for example, as described and shown in applicant&#39;s co-pending patent application serial no. PCT/CA01/00710 published under No. WO 01/87584 filed May 18, 2001, the disclosures of which are incorporated herein by reference. Such sleeve may comprise heat activatable components that require that the metal of the pipe adjacent the weld joint  13  and the coatings  14  and  16  be raised to a range of activation temperatures in order to allow successful installation.  
         [0026]    In one preferred embodiment shown in the drawings, the ends of the coatings  14  and  16 , adjacent the weld joint, have a shroud material  17  wrapped around their periphery. The wrapping of the shroud material  17  corresponds in position to and is slightly wider than the width of the regions of the pipeline coatings  14  and  16  onto which the ends of the above-mentioned heat shrink sleeve are to be shrunk.  
         [0027]    As seen in FIG. 2, each shroud material piece  17  comprises a flexible generally rectangular band  18  provided with end fittings  19  and  21  which cooperate to allow the ends of the bands to be joined together.  
         [0028]    In the most preferred form, each band  18  comprises two thicknesses of SILTEMP P4CSR woven glass fibre mat.  
         [0029]    Each end fitting  19  and  21  comprises a length of metal channel, for example an aluminum extrusion, into which an end of the mat  18  is introduced, and the edges of the channel deformed inwardly from its original configuration in order to secure the mat  18 . One channel  19  may be provided with a pair of upstanding lugs, while the other channel  21  is provided with lugs having pivoting clips  24 . The length of the shroud material  17  is such that it fits snugly around the perimeter of the coating  14  or  16  when the ends are joined together. As seen in FIGS. 3 and 4, the joined together end  19  and  21  can be connected by flipping the clips  24  to engage over the lugs  23 .  
         [0030]    After the lengths of shroud material have been wrapped around the coatings  14  and  16 , and the end fittings have been connected together, a pair of heat shield structures  26  and  27  are applied over the shroud material, as seen in FIG. 1.  
         [0031]    Each shroud structure  26  and  27  comprises in the preferred form a pair of flanges, namely, an axially inner and axially outer radially extending annular flange  28  and  29 , respectively. The flanges  28  and  29  are spaced apart by spacer rods  31  a distance corresponding to the length of the coating  14  or  16  that it is desired to heat.  
         [0032]    Preferably, each axially outer flange  29  has connected to it an outwardly extending cylindrical extension  32 .  
         [0033]    In the preferred form, each heat shield structure, as best seen in FIG. 5 comprises two semi-cylindrical portions  26   a  and  26   b  and  27   a  and  27   b , these portions being hinged together at hinges  33  on one side, and, on an opposite side, being provided with latches  34  that allow the portions to be latched together in a closed position.  
         [0034]    The heat shield structure may be of any heat resistant material for example metal such as steel.  
         [0035]    In the preferred form, as seen in FIG. 1, the opening of the inner flange  28  engages on the outer side of the coating  14  or  16 , while the inner opening of the outer flange  29  and the inner periphery of the extension  32  clamps tightly on the shroud material  17  in the closed position.  
         [0036]    In the course of installation of a sleeve, the steel pipe between the two inner flanges is heated by application of hot gases, preferably from a propane hand torch  36  until a desired temperature is attained. Other heating devices may of course be employed, for example heating devices providing a stream of hot air.  
         [0037]    Similarly, the pipeline coatings  14  and  16  in the zone between each pair of flanges  28  and  29  is heated, again preferably with propane torches  37  until the pipeline coating attains a desired temperature.  
         [0038]    The flange assemblies are then opened and the shroud materials  17  removed and immediately thereafter a heat shrink sleeve is applied over the heated portion and is shrunk tightly around the joint, again preferably by using heat applied directly on the exterior of the sleeve, for example with propane torches.  
         [0039]    During the heating steps, the temperatures of the bare metal and of the coating can be measured using conventional temperature measuring devices, for example thermocouples applied to the surfaces of the metal and to the coatings  14  and  16 , respectively.  
         [0040]    An example of a procedure using the above apparatus and method described in detail with reference to FIGS.  1  to  5  will now be given.  
       Example  
       [0041]    A pipeline had a coating of 2.5 mm thick 3-layer polypropylene, and the bare steel weld joint was 100 mm wide. The procedure was as follows:  
         [0042]    The coating adjacent to both ends of a bare steel weld joint was tightly wrapped with a double wrap of 100 mm wide Siltemp P4CSR.  
         [0043]    A heat shield structure as shown in FIGS.  1  to  5  of the accompanying drawings was clamped over each Siltemp blanket.  
         [0044]    The steel pipe between the two inner flanges was heated with propane hand held torches to approximately 200° C.  
         [0045]    The propane hand torches were then directed between thinner and outer flanges on either end, directing the flame directly at the blanket, until the pipeline coating temperature reached 150 to 160° C.  
         [0046]    The heat shield structures and blankets were removed and immediately thereafter a heat shrink sleeve consisting of a crosslinked polypropylene-based heat shrinkable backing coated inside with a polypropylene based hot melt adhesive was placed over the heated area.  
         [0047]    The heat shrink sleeve was shrunk tightly around the joint using the propane torches.  
         [0048]    Upon removal of the blanket after heating, it was apparent that the surface of the polypropylene was not waxy.  
         [0049]    After completion of the procedure and cooling to ambient temperature, excellent adhesion was observed between the sleeve adhesive and the pipeline coating, and between the sleeve adhesive and the steel.  
         [0050]    While the above description has referred to application of a sleeve to the exterior of a pipeline coating, it will be appreciated that a similar blanket structure and heat shield structure may be used in the application of a patch to effect a repair to a holiday in a pipeline coating.  
         [0051]    For example FIGS. 6 and 7 show a heat shield structure comprising inner and outer endless, for example cylindrical, heat resistant flanges  41  and  42 , respectively, extending away from and preferably substantially normal to the surface of the pipe  43 . Outer cylinder  42  has a transversely outward extension  44 . The radially inner surfaces of elements  41 ,  42  and  44  may be saddle-shaped to conform to the curvature of pipe  43 . Shroud material  46  extends between flanges  41  and  42  and preferably beneath extension  44 . The heat shield structure and shroud material may be formed from materials similar to those employed for the corresponding elements in the apparatus described above with reference to FIGS.  1  to  5 . In use, an appropriately sized circle of damaged coating  47  is removed down to bare metal  43 . The heat shield structure and shroud material is applied as shown in FIGS. 6 and 7. The bare metal  43  is heated through the inner cylindrical shield  41  and the adjacent coating  47  by training a flame into the annular section between cylinders  41  and  42 . Once the desired temperatures are attained, the heat shield and shroud material are removed and a patch of heat activatable repair material is applied.