BACKGROUND OF THE INVENTION

[0001] The present invention relates to reinforced pipe, and more specifically to thermoplastic composite reinforced pipe.

[0002] Thermoplastic composite (TPC) pipe constructions are known and recognized for their strength. Therefore TPC pipe is used in a variety of applications for conveying fluids, especially at relatively high pressures. Typically, TPC pipe includes a thermoplastic liner, a TPC overwrap helically wrapped around the liner, and a thermoplastic jacket over the overwrap. Preferably, all of these layers are thoroughly bonded to one another.

[0003] TPC pipe can be pressure rated up to tens of thousands of pounds per square inch (PSI). Once rated at a specific pressure, it is important that a TPC pipe actually perform to the rating. Failures to do so can have consequences ranging from relatively small leaks to catastrophic failures. Every level of failure, even a relatively small leak, is unacceptable in some application. Consequently, a continuing need exists to identify actual and potential failures, to identify the causes of the failures, and to develop techniques to prevent future similar failures.

SUMMARY OF THE INVENTION

[0004] The present invention includes both the identification of a cause of failure and a number of techniques to prevent future similar failures.

[0005] The identification of a cause of failure is described as follows. Under high internal pressures, the fluid pushes radially outwardly on the pipe; and the tendency of the TPC pipe is to expand circumferentially. However, because the TPC overwrap does not expand, the thermoplastic liner tends to lengthen. This lengthening of the liner pulls on the overwrap that is bonded to the liner, and consequently the lengthening can cause tearing or separation within the overwrap, possibly creating weak points and causing premature failure. Even relatively small tears or separations can have completely unacceptable consequences. Further, the lengthening of the liner can lengthen the entire pipe, causing the pipe to extend beyond its nominal linear dimension and/or creating stress in couplers and other fittings.

[0006] The present invention includes a number of techniques for preventing future failures.

[0007] In one aspect, the TPC pipe includes a thermoplastic pipe liner having a longitudinal axis, a TPC overwrap, and an intermediate layer between the liner and the overwrap. The intermediate layer includes fibers oriented generally parallel to the axis of the liner.

[0008] In another aspect, the TPC pipe includes a thermoplastic liner having a longitudinal axis and a TPC overwrap. The liner includes fibers within or on the liner. The fibers are generally parallel to the axis of the liner.

[0009] In another aspect, the TPC pipe includes a liner having a longitudinal axis, a

TPC overwrap, and a jacket over the overwrap. The pipe also includes longitudinal fibers or other reinforcement adjacent or within one of the liner and the jacket.

[0010] In yet another aspect, a method for forming a TPC pipe includes providing a liner having an axis, applying fibers on or within the pipe liner with the fibers generally parallel to the axis, and applying a TPC overwrap over the liner and fibers.

[0011] In each aspect, the axially oriented fibers resist, and in some cases prevent, lengthening of the liner when the pipe is under pressure. The reduced or prevented liner lengthening reduces or eliminates tearing and separation within the overwrap. And consequently, the axially oriented fibers reduce or eliminate failures. Pipes in accordance with the present invention therefore have improved performance and reliability over pipes known in the art. [0012] These and other features and advantages of the invention will be more fully understood and appreciated by reference to the entire application including the specification, the claims, and the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Fig. 1 is a perspective cutaway view of a reinforced pipe in accordance with a first embodiment of the present invention;

[0014] Fig. 2 is a cross-sectional view of the reinforced pipe, taken along line II-II of Fig. 1 ;

[0015] Fig. 3 is a perspective cutaway view of a reinforced pipe in accordance with a second embodiment;

[0016] Fig. 4 is a cross-sectional view of the second embodiment, taken along line IV- IV of Fig. 3;

[0017] Fig. 5 is a perspective cutaway view of a reinforced pipe in accordance with a third embodiment;

[0018] Fig. 6 is a cross-sectional view of the third embodiment, taken along line VI- VI of Fig. 5;

[0019] Fig. 7 is a perspective cutaway view of a reinforced pipe in accordance with a fourth embodiment;

[0020] Fig. 8 is a cross-sectional view of the fourth embodiment, taken along line VIII- VIII of Fig. 7;

[0021] Fig. 9 is a flowchart of a first method for forming a reinforced pipe;

[0022] Fig. 10 is a flowchart of a second method for forming a reinforced pipe;

[0023] Fig. 11 is a perspective cutaway view of a reinforced pipe in accordance with a fifth embodiment; [0024] Fig. 12 is a cross-sectional view of the fifth embodiment, taken along line XII- XII of Fig. 11;

[0025] Fig. 13 is a perspective cutaway view of a reinforced pipe in accordance with a sixth embodiment; and

[0026] Fig. 14 is a cross-sectional view of the sixth embodiment, taken along line XIV- XIV of Fig. 13.

DESCRIPTION OF THE CURRENT EMBODIMENTS

[0027] The invention as contemplated and disclosed herein includes a reinforced pipe and a related method of manufacture. With reference to Figs. 1 and 2, a reinforced pipe in accordance with one embodiment is illustrated and generally designated with reference numeral 10. The reinforced pipe 10 includes a liner or inner tubular member 12, an overwrap or radial reinforcing layer 14, and an intermediate layer 16 between the liner 12 and the reinforcing layer 14.

[0028] More particularly, the inner tubular member 12 preferably is a thermoplastic extrusion, for example, of a high density polyethylene (HDPE). The inner tubular member 12 includes a sidewall 18 defining an inner surface 20 and an outer surface 22. The outer surface 22 is spaced apart from the inner surface 20 by a desired sidewall thickness. The inner surface 20 defines a conduit for a moving fluid, for example an aqueous fluid, a gaseous fluid, and combinations thereof.

[0029] The radial reinforcing layer 14 may be on the outer surface 22 of the tubular member 12. The reinforcing layer 14 may be formed of any material adapted to increase the burst strength of the tubular member 12. In the present embodiment, the reinforcing layer 14 is a thermoplastic composite (TPC) tape helically wound about the exterior of the tubular member 12 and the intermediate layer 16. The thermoplastic composite tape may include directional fibers and/or woven fibers. The fibers may include for example carbon, aramid, fiberglass, aluminum or titanium. Further, the reinforcing fibers may be disposed in a thermoplastic matrix material, for example polyamide, polyethylene terephtalate (PET), polyphenylene sulphide (PPS), polybutylene terephthalate (PBT), polysulfone, or polycarbonate.

[0030] Additional layers can also be included in the reinforced pipe 10. As shown in

Fig. 1 for example, an exterior layer or jacket 24 can be added to the exterior of the reinforcing layer 14. The jacket 24 can be fused to the reinforcing layer 14 to form a multilayer TPC pipe for high pressure applications.

[0031] In a first embodiment, illustrated in Figs. 1 and 2, the intermediate layer or longitudinal reinforcement, is disposed between the tubular member 12 and the radial reinforcing layer 14. The intermediate layer is defined by strips 16 which are parallel to a longitudinal axis 30 of the tubular member 12. As illustrated, the intermediate layer is circumferentially continuous, encircling the entire tubular member 12. Further, the strips 16 can be thermally bonded to the tubular member 12, and the reinforcing layer 14 can be thermally bonded to the strips 16. As illustrated, the intermediate layer is on the exterior of the liner 12. Alternatively, the intermediate layer may be on the interior of the liner 12.

[0032] Referring now to Figs. 3 and 4, in a second embodiment, the intermediate layer is again defined by strips 16 which are generally parallel to the longitudinal axis 30 of the tubular member 12. Unlike the first embodiment, the strips 16 are positioned at intervals around the circumference of the tubular member 12, defining spaces 32 between the strips 16 of the intermediate layer. The strips 16 and spaces 32 may be arranged in any suitable repeating pattern, regular or irregular. For example, as illustrated in Fig. 3, the intermediate layer may include three strips 16. Other patterns, be they repeating or random, are within the scope of the invention. The intermediate layer may be thermally bonded to the tubular member 12; and the reinforcing layer 14 may be thermally bonded to both the intermediate layer and the tubular member 12 where it is exposed within the spaces 32. References to bonding in this application assume similar chemical affinity or polarity.

[0033] A third embodiment of the pipe is illustrated in Figs. 5 and 6 where the intermediate layer is within the extruded tubular member 12. In this embodiment, the intermediate layer is defined by a plurality of unidirectional fiber elements 34 which are oriented parallel to the longitudinal axis 30 of the tubular member 12. The unidirectional fiber elements 34 may be circular or virtually any other cross-sectional shape, and may be placed in the tubular member 12 during the extrusion process. Further, the elements 34 are positioned at intervals around the circumference of the tubular member 12; the intervals may be regular or irregular, and also may be spaced or overlapping.

[0034] A fourth embodiment of the pipe is illustrated in Figs. 7 and 8. The intermediate layer is again defined by strips 16 that extend parallel to the longitudinal axis 30 of the tubular member 12. However, in this fourth embodiment, the strips 16 are within the extruded tubular member 12. The strips 16 may be placed in the tubular member 12 during the extrusion process and are positioned at intervals around the circumference of the tubular member 12.

[0035] The intermediate layer may be a TPC, for example, similar to the reinforcing layer 14. In some of the embodiments, the intermediate layer may include generally unidirectional fibers (e.g. fiberglass) within a thermoplastic. In other embodiments, the intermediate layer may be formed of wire, glass, DuPont's Kevlar, or any other suitable material.

[0036] Referring now to the flow chart of Fig. 9, a first method for forming a reinforced pipe includes extruding a thermoplastic material into a tubular member or preform at step 50. The tubular member is preferably circular in cross section and is formed of HDPE in an exemplary embodiment, but can include other suitable materials as desired. [0037] At step 52, a longitudinal intermediate layer is applied to the outer surface of the formed tubular member. The longitudinal intermediate layer may be a TPC tape applied in strips that are oriented parallel to a longitudinal axis of the tubular member. The strips may form a continuous circumferential layer that encircles the entire preform, or may be applied to include spacing or intervals between the strips, as described above. As an alternative or a supplement, the intermediate layer may be placed within the wall of the tubular member during the extrusion step 50.

[0038] A radial reinforcement layer is wrapped around the intermediate layer and tubular member at step 54. The longitudinal and radial reinforcement layers may be made of substantially the same or similar materials. Optionally, the radial reinforcement layer may be made of a material that is different from the longitudinal reinforcement layer.

[0039] Finally, an optional jacket layer can be applied as an extrudate over the radial reinforcing layer at step 56. Heat may be applied to the reinforced pipe to thermally bond the layers together at any or multiple points during the described method.

[0040] Referring now to the flow chart of Fig. 10, a second method for forming a reinforced pipe includes co-extruding at step 60 a polymeric material and a longitudinal intermediate layer or material. The polymeric material of an exemplary embodiment is HDPE, but the material can be or include other suitable materials as desired. The longitudinal intermediate layer may include, for example, fibers, threads, rods, or strips that are oriented generally parallel to the longitudinal axis of the tubular member.

[0041] At step 64 a radial reinforcing layer is wrapped around the tubular member.

The intermediate and radial reinforcement layers may be made of substantially the same or similar material to that of the tubular member. Optionally, the intermediate layer may be made of a material that is different than that of the tubular member.

[0042] Further, once the radial reinforcing layer is applied, an optional jacket layer can be applied as an extrudate over the radial reinforcing layer at step 66. Heat may be applied to the reinforced pipe to thermally bond the layers together at any or multiple points during the described method.

[0043] A fifth embodiment of the pipe, illustrated in Figs. 11 and 12, includes unidirectional fiber elements 34 within the jacket 24. The unidirectional fiber elements 34 are oriented parallel to the longitudinal axis 30 of the pipe 10. The unidirectional fiber elements 34 may be placed in the jacket 24 during the extrusion process and may be positioned at intervals around the circumference of the jacket 24; the intervals may be regular or irregular, and also may be spaced or overlapping. The pipe 10 may include, as a supplement or as an alternative, unidirectional fiber elements 34 within the tubular member 12, as described above and illustrated in the drawings. Instead of or in addition to the elements 34 being within the liner 12 and/or the jacket 24, elements (not shown) may be between the liner 12 and the overwrap 14 and/or between the jacket 24 and the overwrap 14.

[0044] A sixth embodiment of the pipe, illustrated in Figs. 13 and 14, includes strips

16 within the jacket 24. The strips 16 are parallel to the longitudinal axis 30 of the pipe 10. The strips 16 may be placed in the jacket 24 during the extrusion process and are positioned at intervals around the circumference of the jacket 24; the intervals may be regular or irregular, and also may be spaced or overlapping. The pipe 10 may also include, as a supplement or as an alternative, strips 16 within the tubular member 12, as described above and illustrated in the drawings. Instead of or in addition to the strips 16 being within the liner 12 and/or the jacket 24, strips (not shown) may be between the liner 12 and the overwrap 14 and/or between the jacket 24 and the overwrap 14.

[0045] Under high pressures, the tendency of the pipe is to expand radially.

However, the radial reinforcing layer, which is within or on the liner, does not stretch, and therefore prevents the reinforced pipe from expanding circumferentially. The longitudinal reinforcement layer or material also does not stretch, and therefore prevents the pipe from expanding longitudinally or lengthwise. Therefore, the pipe is reinforced in both the radial and lengthwise directions, providing dimensional stability to the reinforced pipe even when subjected to high pressures.

[0046] The above descriptions are those of the current embodiments of the invention.

Various alterations and changes can be made without departing from the spirit and broader aspects of the invention as defined in the appended claims, which are to be interpreted in accordance with the principles of patent law including the doctrine of equivalents. Any reference to elements in the singular, for example, using the articles "a," "an," "the," or "said," is not to be construed as limiting the element to the singular.