Patent Publication Number: US-2022221087-A1

Title: Helically wound pipe and related method

Description:
TECHNICAL FIELD 
     This application relates generally to ribbed pipe structures and, more specifically, to helically wound ribbed pipe structures with a helical seam. 
     BACKGROUND 
     Plastic pipes can be made by helically winding a plastic strip having a series of spaced apart upstanding ribs extending longitudinally of the strip, either at room temperature or at an elevated temperature where the plastic becomes more flexible. U.S. Pat. No. 7,004,202, the entirety of which is incorporated herein by reference, describes a composite strip having upstanding plastic ribs encasing an elongate reinforcing member. Per  FIG. 1 , the helical winding brings together opposed sides  10 ,  12  of the strip in an overlapping manner to form a helical joint, which overlap can be bonded using a plastic seam weld  14 .  FIG. 1  illustrates the typical plastic seam weld  14  of the helical seam, with the plastic seam weld material shown in crosshatch. Some of the seam weld material is typically squeezed out beyond the overlapping portions as shown. Under extreme conditions (e.g., improper pipe handling or improper backfilling atop the pipe), pipe wall fracture alongside the helical joint may occur, as reflected by fracture  15 . 
     It would be desirable to provide a helically wound pipe with a helical joint having improved performance under extreme conditions. 
     SUMMARY 
     In one aspect, a pipe includes an elongate composite plastic strip having a base portion with an upper surface and a lower surface, a plurality of ribs extending upward from the upper surface of the base portion, each rib formed by a reinforcement strip within plastic material, the composite plastic strip having a first side and a second side, wherein the composite plastic strip wound into a tubular pipe form with the upper surface and the ribs at an exterior of the tubular pipe form, with a first portion of the first side overlapping a first portion of the second side along a helical joint, and with a plastic seam weld applied between the overlapping first portions for bonding the overlapping first portions together. A plastic overweld extends over the overlapping first portions of the first side and the second side and over both a second portion of the first side and a second portion of the second side, wherein the second portion of the first side is adjacent to the first portion of the first side and does not overlap with any part of the second side, and wherein the second portion of the second side is adjacent to the first portion of the second side and does not overlap any part of the first side. 
     In another aspect, a method of manufacturing helically ribbed pipe involves: using an elongate composite plastic strip having a base portion having an upper surface and a lower surface, a plurality of ribs extending upward from the upper surface of the base portion, each rib formed by a reinforcement strip within plastic material, the composite plastic strip having a first side and a second side; helically wrapping the composite plastic strip into a tubular pipe form with the upper surface and the ribs at an exterior of the tubular pipe form and with a first portion of the first side overlapping a first portion of the second side at a helical joint, and, during the wrapping, applying a plastic seam weld between the overlapping first portions for bonding the overlapping first portions; applying pressure to the overlapping first portions of the first side and the second side to compress the plastic seam weld; and after the application of the pressure, applying a plastic overweld that extends over the overlapping first portions of the first side and the second side and over both a second portion of the first side and a second portion of the second side, wherein the second portion of the first side is adjacent to the first portion of the first side and does not overlap with any part of the second side, and wherein the second portion of the second side is adjacent to the first portion of the second side and does not overlap any part of the first side. 
     The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will be apparent from the description and drawings, and from the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a prior art pipe section showing a helical pipe joint for a prior art pipe formed by helical winding of a composite plastic strip; 
         FIG. 2  shows a pipe section of a pipe according to the present application; 
         FIG. 3  shows the pipe section of  FIG. 2 , but with a pipe body wall fracture covered by the overweld; 
         FIG. 4  shows a pipe section of another pipe according to the present application; 
         FIG. 5  shows a pipe section of another pipe according to the present application; and 
         FIG. 6  shows a schematic depiction of one embodiment of a winding cage set-up for formation of a pipe according to the present application. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 2 , a pipe  20  is formed of an elongate composite plastic strip  22  having a base portion  24  with an upper surface  26  and a lower surface  28 . Here, the base portion  24  is formed entirely of plastic material, such as HDPE, but the base portion could be formed with internal reinforcement (e.g., metal) in some sections. A plurality of ribs  30  extend upward from the upper surface  26  of the base portion. Here, each rib  30  is formed by a metal reinforcement strip  30   a  within surrounding plastic material  30   b . The strip  22  has opposite elongated sides  32 ,  34  and is wound into a tubular pipe form with the upper surface  26  and the ribs  30  at an exterior of the tubular pipe form. An edge portion  32   a  of the side  32  overlaps with an edge portion  34   a  of the opposite side  34  along a helical joint  36 . A plastic seam weld  38  is applied between the overlapping portions  32   a  and  32   b  for bonding the overlapping portions together. 
     A plastic overweld  40  is also provided and extends over the overlapping edge portions  32   a ,  34   a  of the two sides  32  and  34 . The overweld  40  also extends over both an adjacent portion  32   b  of side  32  and adjacent portion  34   b  of side  34 . Portion  32   b  does not overlap with any part of side  34 , and portion  34   b  does not overlap with any part of side  32 . Both the seam weld  38  and the overweld  40  may also be formed of plastic material, such as HDPE, though other variations are possible. 
     The plastic overweld  40  is bonded to the exterior facing surface of each of portion  34   a , a part of the plastic seam weld  38  that is external of the overlapping portions  32   a  and  34   b , the adjacent portion  32   b  and the adjacent portion  34   b . As shown, the overlapping portions are between rib  30 - 1 , which is proximate to and runs along the side  32 , and rib  30 - 2 , which is proximate to and runs along the side  34 . Here, the plastic overweld  40  extends onto each of a transition region  42  from the base portion to the rib  30   a  and a transition region  44  from the base portion to the rib  30   b . Transition region  42  is defined by a thickening T 1  of plastic of the base portion and the transition region  44  is defined by a thickening T 2  of plastic of the base portion. Each thickening T 1 , T 2  defines a respective exterior outwardly curved surface segment  42   a ,  44   a  adjacent the respective rib  30   a ,  30   b . As seen in  FIG. 2 , the overweld provides sound bonding of the helical joint  36  to help prevent separation of the sides  32  and  34  and overlaps the region where a fracture under extreme conditions might occur, strengthening the overall pipe structure in that region. Thus, the overweld  40  reduces the chance of fracture under the extreme conditions. Moreover, as suggested in  FIG. 3 , if a pipe wall fracture  45  does occur, the overweld  40  can preserve the integrity of the pipe wall. 
     Referring now to  FIG. 4 , a pipe  20 ′ includes a seam weld  38 ′ and overweld  40 ′, where the overweld  40 ′ has a slightly different profile than that shown in  FIG. 2 . In  FIG. 2 , the exterior surface of the overweld  40  is generally curved across it entire width or span of the joint  36 . However, in  FIG. 4 , the overweld  40 ′ of joint  36 ′ includes a central segment  50  that is generally planar, with a relatively uniform thickness T 50 . Side segments  52  of the overweld  40 ′ begin with a larger thickness (e.g., T 52 ), with the thickness tapering down to the very edges of the overweld. A combined thickness of the overlapping side portions and the seam weld therebetween is shown as TC 1 . A combined thickness of the overlapping side portions, the seam weld therebetween and the overweld is shown as TJ 1 . 
     Referring now to  FIG. 5 , a pipe  20 ″ includes a seam weld  38 ″ and overweld  40 ″, where the overweld  40 ″ of joint  36 ″ includes a central segment  60  that is generally planar, with a relatively uniform thickness T 60 . Side segments  62  of the overweld  40 ″ begin with a larger thickness (e.g., T 62 ), with the thickness tapering down to the very edges of the overweld. A combined thickness of the overlapping side portions and the seam weld therebetween is shown as TC 2 . 
     The central segment  50 ,  60  of the plastic overweld may have a thickness T 50 , T 60  of at least 0.150 inches, such as at least 0.180 inches. The central segment  50 ,  60  of the plastic overweld may have a thickness T 50 , T 60  that is equal to or greater than thirty percent (30%) of the combined thickness T 52 , T 62  of the overlapping portions and the seam weld therebetween (e.g., equal to or greater than fifty percent or equal to or greater than seventy percent of the combined thickness of the overlapping portions and the seam weld therebetween). The central segment  50 ,  60  of the plastic overweld has a thickness T 50 , T 60  and the adjacent side segments  52 ,  62  of the plastic overweld have respective side segment thicknesses T 52 , T 62 , and each side segment thickness T 52 , T 62  is at least thirty-five percent larger than the thickness T 50 , T 60 . The foregoing relative dimensions provide advantageous joint performance. 
     Referring now to  FIG. 6 , a schematic depiction of the winding operation for the composite strip shows a winding cage  70  with a winding direction  72 . As the elongate composite plastic strip is wound using about the winding cage, the opposed sides of the strip are pre-heated (e.g., using heated air) in zone  74  to prepare for application of the seam weld, which occurs in zone  76 . The pre-heating facilitates bonding of the plastic of the seam weld to the plastic of the sides. After application of the seam weld, the overlapping portions of the sides are brought together and pressure applied in zone  78 , using compression rollers at the inner and outer sides of the joint. This application of pressure causes some plastic of the seam weld to be squeezed out beyond the overlapping side portions. In zone  80 , another pre-heat occurs at the exterior face of the joint to prepare for application of the overweld, which occurs in zone  82 . The overweld is applied with a pressure head the defines the exterior surface contour of the final overweld. 
     In  FIGS. 4 and 5  above the strip is shown with upstanding ribs that do not include inserted metal reinforcement. However, in a typical pipe such ribs will include the metal reinforcement that is, typically, fully encased in plastic. 
     It is to be clearly understood that the above description is intended by way of illustration and example only, is not intended to be taken by way of limitation, and that other changes and modifications are possible.