Abstract:
A method of joining the ends of two thermal insulated pipes or conduits where each conduit has an inner pipe that extends axially beyond a middle tubular layer of thermal insulation material and an outer tubular layer of protective jacket. Before the ends of the inner pipe are welded together, an end cap blank having a central aperture is fit onto each inner pipe until it covers the exposed end of the middle and outer layers. Each end cap blank initially has the area of its central aperture pressed and deformed axially to form a tapered collar. Subsequently the inner pipe of a conduit presses and further deforms the tapered collar to define a substantially axially extending collar that is sealingly fit about the inner pipe protruding therethrough to prevent escape of toxic gases from the insulation layer during the welding process, as well as to protect the insulation layer from moisture in the environment.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to thermal insulated pipes for conveying various fluids and to thermal pre-insulated pipe systems, such as district heating and cooling pipe systems and steam and other industrial pipe systems, and more particularly to methods and components for joining such thermal pre-insulated pipes.  
         BACKGROUND OF THE INVENTION  
         [0002]    A typical thermal pre-insulated pipe or conduit is prefabricated and includes a fluid-conducting inner pipe surrounded by one or more tubular layers of thermal insulating material such as rigid polyurethane foam, which in turn is surrounded by an outer sleeve serving as a protective layer. These pipes are manufactured in predetermined lengths whose ends are joined as needed.  
           [0003]    Prior to such junction a portion of the thermal insulation layer and the protective jacket on the end of each pipe to be joined is removed or omitted to expose an end portion of the inner pipe, usually made of steel, which extends axially beyond the end face of the insulating layer and jacket. These inner pipe ends are joined, usually by welding, with a tubular space remaining radially outward of the joined inner pipes and extending axially between the opposing end faces of the thermal insulating layers. This space is filled with new thermal insulating layer by various techniques, a common one being to encase the area with a sleeve-like collar and introduce therein thermal insulating material in fluid form which foams and hardens.  
           [0004]    The welded junction of the steel inner pipes, the tubular section of new thermal insulating material, and the tubular collar encasing the section of new insulating material, are then covered by a protective sleeve which extends axially over and seals onto the original outer sleeve portions respectively of the joined conduits.  
           [0005]    The prior art includes a variety of sealing techniques and materials of hot melt sealants, mastics, resins, adhesives, tapes and shrink-wraps to seal these junctions from intrusion of moisture or other contaminants which might damage the thermal insulating material or the inner pipe or enter the inner pipe. However, damage to the insulating material has been occurring before the junction is sealed, namely during the process of welding the inner pipes. Especially during gas welding of steel inner carrier pipes, the heat generated may cause liberation of chemical substances from the foam insulation material, thus damaging the insulating material and/or producing toxic gases which escape from the insulating material and present a hazard to the welder. Also from the welding process hot cinders or other particulate matter will melt or otherwise damage the insulating material.  
           [0006]    Moving the end faces of the exposed foam insulating material farther from the weld zone has been considered; however, certain manufacturing and cost considerations due to well-established industry standards dictate maintaining this distance as short as possible. Thus, there is resistance in this industry to change in the length of the welding zone. One attempt to overcome this problem has been to apply end caps to cover the end faces of the insulating material during the welding process. However, standard end caps are insufficient to prevent escape of toxic gases from the insulation layer during the welding processes which form these insulated pipe junctions.  
           [0007]    For more clearly and more conveniently describing these pipe junctions certain terminology will be used as follows. The exposed inner pipe has a “lead end” which is the terminal end welded to the lead end of a corresponding inner pipe. The exposed inner portion of the inner pipe also has a rear part where it meets and extends outward from the “end face” of the tubular layer of the insulating material that is exposed in a typical thermal insulated conduit. Adjacent and extending rearward of this end face is the “lead edge” of the tubular layer of heat insulating material and of the outer sleeve.  
           [0008]    An end cap when used to cover or overlie the exposed “end face” of the thermal insulating layer includes a “face plate” which is the flat or bowed disc having a generally central aperture which has an “inner diameter” for receiving the exposed inner pipe. The face plate of such end cap has at its outer circumferential periphery an axially rearwardly extending “outer sleeve or flange” having an “outer diameter” that overlies the lead edge of the existing outer sleeve that covers the thermal insulating layer near its end face. Usually, there is at the periphery of the central aperture of the faceplate of the end cap a forwardly axially extending “inner sleeve or flange” that overlies the rear part of the exposed inner pipe. Because thermal insulated pipes are well standardized in sizes, an end cap, if economically viable, must have its central aperture sized to readily receive the lead end of the inner pipe and must have its outer flange sized to fit onto the lead edge of the original outer sleeve. An attempt to achieve an effective seal between the inner and outer sleeves of an end cap with an inner pipe and an outer sleeve respectively of a thermal insulation conduit, included use of circular rings or ribs on the respective sleeves extending radially inward. It has been found, however, that these couplings are not sufficiently tight and sealed. This is because of the dimensional clearances required in order for these prefabricated end caps and insulated conduits to readily slide one over the other when they are coupled. Thus, gaps occur with the result that toxic gases produced in the insulation layer from the welding stage frequently discharge from the end face of the thermal insulating foam, creating a hazard for the welder.  
           [0009]    Techniques to better seal these pipe junctions, both during the welding and after the new insulation material is formed around the weld, are disclosed in numerous prior art patents, such as U.S. Pat. Nos. 4,629,216; 4,514,241; 4,162,083; 5,002,716; 3,877,491; 4,610,740; and EP 0 708 290 A3. Prior art end caps are shown in FIGS.  1 - 6  shown below.  
         OBJECTS AND SUMMARY OF THE INVENTION  
         [0010]    A principal object of the present invention is to provide a technique for joining thermal insulated pipe which both reduces or avoids contamination of, and escape of toxic gases from, the insulation associated with welding. It is a further object to provide a new pipe joining technique that allows retaining current standardized conduit compositions, retaining diameter and length dimensions of exposed inner pipe and retaining current welding procedures.  
           [0011]    To achieve these objectives one approach is to cover and protect the exposed end face of the thermal insulation foam with plastic end caps that are custom fitted by plastic deformation at the time of installation to each pipe.  
           [0012]    One method for such custom fitting is to utilize the inner pipe lead end itself to deform the central aperture in the end cap into a collar, to thus produce an exact interference fit between the collar and the inner pipe. A further and supplemental method is to select plastic material for the end cap which will heat shrink at both its outer and inner diameters, namely at its inner and outer sleeves to provide more secure seals.  
           [0013]    Another objective is to select for the end cap plastic material that will expand at a predetermined temperature zone for said deformation. Suitable plastics include cross-linked and non-cross-linked PE, PP and PVDF, in addition to PTFE.  
           [0014]    The new end caps and new joining procedure provide better protection of the insulation from welding heat and contaminants and reduce escape of toxic gases from the insulation, during welding and thereafter. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]    A more complete appreciation of the present invention and the advantages thereof will be readily understood by reference to the following detailed description, when considered in connection with the accompanying drawings in which:  
         [0016]    [0016]FIG. 1 is a schematic elevation view of a prior art welding stage of joining pre-insulated pipes,  
         [0017]    [0017]FIG. 2 is a schematic elevation view similar to FIG. 1 showing subsequent stages of joining pre-insulated pipes,  
         [0018]    [0018]FIG. 3 shows schematically a first prior art pre-insulated end pipe installation,  
         [0019]    [0019]FIG. 4 shows schematically a second prior art pre-insulated end pipe installation,  
         [0020]    [0020]FIG. 5 shows schematically an end cap used in FIG. 3,  
         [0021]    [0021]FIG. 6 shows schematically a variation of the end cap shown in FIG. 5,  
         [0022]    FIGS.  7 - 11  show schematic cross-sectional views of a sequence of steps of the pipe-joining method of the present invention, wherein,  
         [0023]    [0023]FIG. 7 shows schematically a preliminary step of the method of the new invention,  
         [0024]    [0024]FIG. 8 shows schematically a step of initial deformation of the end cap by a mandrel in accordance with the invention,  
         [0025]    [0025]FIG. 9 shows schematically a step of initial engagement of the end cap with an inner pipe in accordance with the invention,  
         [0026]    [0026]FIG. 10 shows schematically a step of penetration by an inner pipe and further deformation of the end cap in accordance with the invention,  
         [0027]    [0027]FIG. 11 shows schematically a completed installation of an end cap onto an inner pipe, and  
         [0028]    [0028]FIG. 12 shows schematically a completed pipe junction using the new end caps.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0029]    Referring now to the drawings, like reference characters designate identical or corresponding parts throughout the several views. To better describe this new invention, reference will first be made to FIGS.  1 - 6  which illustrate various prior art pipe joining techniques and structural components. In FIG. 1 is shown an intermediate step in the joining of two heat insulated pipes  12 A and  12 B. A typical thermal insulated conduit  10 A consists of a central inner pipe  12 A of steel surrounded by a insulation layer  14 A of polyurethane and similar insulation (“PUR”) foam with its end face  15 A and a protective outer sleeve  16 A of plastic sheet such as high density polyethylene (“HDPE”). Coaxial with conduit  10 A is corresponding conduit  10 B with its inner pipe  12 B, insulation layer  14 B and outer sleeve  16 B.  
         [0030]    Inner pipes  16 A and  16 B respectively have exposed sections  17 A and  17 B and lead ends  18 A and  18 B which are joined at weld junction  20 . The exposed sections  17 A and  18 A of the inner pipes each have length L, and the total length 2L for the two joined pipes is considered the welding heat zone extending between the exposed end faces  15 A,  15 B of the heat insulation foam. Despite a heat zone of about 150 mm for gas welding and about 70 mm for CO 2 , heat and solid contaminants from the welding may travel into the insulation layers from which toxic gases are produced and escape into the welding zone.  
         [0031]    [0031]FIG. 2 shows schematically a prior art junction of conduits  10 A and  10 B with weld joint  20  and tubular space  22  between end faces  15 A,  15 B filled with new insulation foamed-in material  24 , which in turn is encased in a tubular collar or bridging sleeve  26 , which may be formed of a pair of axially joined half-collars or by a mastic seal wrap. Encasing the collar  26  is a tubular segment  28  of plastic sheet which has supplemental seal elements of an annular hot melt  30  and a mastic outer seal  32 .  
         [0032]    FIGS.  3 - 6  show techniques of using a known end cap formed of PE, PP or other appropriate plastic intended to protect end face  16 B of the insulating layer  14 B from solid contaminants during welding. In FIG. 3 end cap  35  has radially extending face plate  35  with forwardly extending inner sleeve or flange  36  dimensioned to slip over a standard size of inner pipe  12 B, and a rearwardly extending outer sleeve or flange  37  dimensioned to slip over the leading edge of a standard size of outer sleeve  38 . FIG. 4 shows an end cap  39  similar to end cap  34  of FIG. 3, but with an outer sleeve  40  situated radially inward of outer sleeve  38 .  
         [0033]    [0033]FIG. 5 shows an end cap as used in FIG. 3 with its forward sleeve  36  and its rearward sleeve  37 . FIG. 6 shows an alternative version of an end cap  41  for use with the heat insulation pipe of FIG. 3. In FIG. 6 this end cap has inward extending circumferential sleeve element  42  to sealingly engage the outer surface  42 A of said outer sleeve in FIG. 3, and sleeve element  43  to sealingly engage the outer surface  43 A of said inner pipe  12 B in FIG. 3.  
         [0034]    FIGS.  7 - 11  illustrate a sequence of steps for forming a tapered collar  57  in an end cap blank  50  and subsequently further forming this tapered collar to sealingly fit onto an inner pipe of a heat insulated pipe section prior to joining it to another pipe section. The steps include: (a) beginning with an “initial end cap blank”; (b) forming it into a “final end cap blank” with a tapered collar; (c) coupling this final end cap blank into an inner pipe which extends through and expands the collar, thereby establishing a final end cap (also simply called “end cap”) sealingly engaged to the inner pipe.  
         [0035]    According to the invention, an initial end cap blank  50  is prefabricated of a plastic such as PE or PP to have a generally radially extending face plate  51 , and a rearwardly extending outer sleeve  52  having radially inwardly directed seal rings  53 . In the center of the face plate is a central aperture  54  whose diameter d 1  is less than the outer diameter d 2  of the inner pipe  12 . Referring to FIG. 8, in accordance with the invention, a tapered mandrel  56  is axially inserted into and through the aperture  54  where it deforms the edges of the aperture into a tapered conical collar  57  having inner diameter d 3  which is greater than original diameter d 1 , thus establishing final end cap blank  50 A. Instead of the tapered mandrel, the actual carrier pipe may be used to deform the edges of the aperture into the tapered collar. This procedure could be illustrated schematically by FIGS. 7, 9,  10  and  11 , thus omitting the stage illustrated by FIG. 8. This expansion may be in the range of about 5-40% of the original diameter d 1 . Such end caps are made with various standardized tapered collars  57  to be ready for application in the field or in a factory environment.  
         [0036]    [0036]FIG. 9 shows an early stage of application in a field installation of one such new end cap blank  50 A to an inner pipe  12  whose insulation layer  59  has been omitted or removed to expose length L of the central inner pipe  12 . The tapered conical collar preformed in the step of FIG. 8 has an inner diameter d 3  less than the outer diameter d 2  of pipe  12 ; this collar has an outer diameter d 4  greater than the outer diameter d 2  of pipe  12 . In this FIG. 9 the lead end  60  of the inner pipe  12  is axially aligned with aperture  54  and is urged axially in direction “a” into engagement with the tapered collar or lip  57  or, more practically, the end cap blank  50 A is urged in direction “b”, onto the lead end  60  of the inner pipe. With further axial urging seen in FIG. 10 the lead end  60  of pipe  12  further deforms the collar  57 , now the end cap blank&#39;s inner sleeve, to have longer axial length and greater diameter.  
         [0037]    [0037]FIG. 11 shows the inner pipe  12  to have fully penetrated the end cap blank  50 A thus forming the final end cap. The tapered collar  57  is now sealingly form-fit onto the inner pipe  12  with a substantially gas impermeable seal along the surface region  61 . The outer sleeve  52  of the end cap is snugly sealed to the outer sleeve  16 B of the conduit in the usual manner. The expansion of the base by the mandrel alone or by the mandrel and subsequently by the inner pipe may be the range of about 5-40% of the original diameter d 1 .  
         [0038]    [0038]FIG. 12 illustrates a pair of the final end caps  50 A,  50 B as developed in FIGS.  7 - 11  and now applied to a pair of lead ends  15 A,  15 B of inner pipes  12 A,  12 B joined at weld junction  66 . The inner collar  57 A of final end cap  50 A, for example, is tightly sealed about the inner pipe  12 A, and end face  16 A is filly covered and protected by face plate  51 A of the final end cap. The heat zone L+L is maintained the same as before to allow use of industry-standardized pipes. The tight seals created between the inner pipes and formed collars of the final end caps prevent the escape of toxic gases from the heat insulation layer during welding.  
         [0039]    After a pair of final end caps  50 A,  50 B is installed onto the lead ends  15 A,  15 B of opposing inner pipes and the welding of the junction  66  has been completed, a collar  70  is positioned to encompass the annular space  72  between the face plates  51 A,  51 B of the opposing end caps. For convenience, such a collar may comprise a pair of axially split and hinged half-collars. Radial spacers, shoulders or other elements (not shown) may be used to accurately position such a collar about this annular space, and then heat insulating material is introduced by “foaming in” via inlet  80  with air outlet  81  or other known techniques. Finally, an outer protective sleeve  74  is positioned or wrapped about the bridging collar  70  with opposite end edges  76 A,  76 B overlying ends  78 A,  78 B of the original conduits where they are sealed circumferentially via known techniques and materials such as hot melt  30  and mastic  32 .  
         [0040]    To enhance the sealing fit of an end cap&#39;s inner sleeve  57  about the inner pipe  12 B, and the end cap&#39;s outer sleeve  52  about the original outer sleeve  16 B (see FIGS. 10 and 11), various plastics may be selected because of special or unique characteristics regarding temperatures at which the plastic compositions expand and/or shrink, particularly during the steps when a collar is being formed in the end cap blank&#39;s face plate and the end cap blank is being coupled onto an inner pipe. These temperature-related properties become applicable at the time of initial deformation of the end cap blank as described with respect to the steps illustrated in FIGS. 7 and 8, and at the time of final deformation into a sealing fit as described with respect to the steps illustrated in FIGS.  9 - 11 , as further described below.  
         [0041]    These end cap blanks may, for example, be made from cross-linked (“C-L”) or non-cross-linked (“N-C-L”) PE, PP and/or PVDF or from PTFE, selected for the temperature at which each end cap blank will be expanded and deformed first by the mandrel and later by the inner pipe or expanded by the inner pipe only. The following are non-exclusive specific examples of end cap blank compositions and temperatures at which they are expanded.  
                                                                     Material   Temperature                           N-C-L PE   Below 120° C.           N-C-L PP or PVDF   Below 160° C.                    PTFE   Below 260° C.           C-L   PE   Above 120° C.           C-L   PP or PVDF   Above 160° C.                      
 
         [0042]    The N-C-L end cap blanks which are expanded below specified temperatures will shrink spontaneously as the temperature rises to achieve a tight fit. The C-L end cap blanks which are expanded above specified temperatures will shrink to the desired fit as the temperature drops.  
         [0043]    End cap blanks of the present invention are made by well known procedures, such as injection molding or blow molding, and have dimensions before deformation onto an inner pipe in the general range of: outer diameter (corresponding to jacket):  
                                       outer diameter (corresponding to jacket):    60 mm to 1200 mm       inner diameter-bore    20 mm to 325 mm       (corresponding to carrier pipe):       wall thickness (end cap):   0.4 mm to 5 mm       axial front flange length (at jacket diameter):     5 mm to 100 mm       axial rear flange length (at carrier pipe):     0 mm to 4 mm                  
 
         [0044]    The end caps may be treated to enhance their protective capability by the appropriate coating or “grafting” to inhibit them from burning or melting due to the exposure of the welding operation.  
         [0045]    With this new technique and end cap structure, the time, effort and cost to protect the heat insulation material during and after welding is reduced, while the effective protection against escape of toxic gases is enhanced. Furthermore, standard sizes of conduit, standard welding procedures and standard outer sealant can all be maintained without change, new cost or new learning requirements.  
         [0046]    Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings and disclosure. Accordingly, it is understood that other embodiments of the invention are possible within the scope of the claims appended hereto.