Patent Application
20140238525
The present invention relates to reinforced pipe, and more specifically to thermoplastic composite reinforced pipe.
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.
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.
The present invention includes both the identification of a cause of failure and a number of techniques to prevent future similar failures.
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.
The present invention includes a number of techniques for preventing future failures.
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.
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.
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.
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.
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.
The invention as contemplated and disclosed herein includes a reinforced pipe and a related method of manufacture. With reference to
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.
The reinforced pipe 10 includes a reinforcing layer 14. The reinforcing layer 14 includes an inner surface facing the outer surface 22 of the tubular member 12. The reinforcing layer 14 can include any material adapted to increase the burst strength of the tubular member 12. In the present embodiment, the reinforcing layer 14 preferably is a TPC tape helically wound about the exterior of the tubular member 12 and the intermediate layer 16. The thermoplastic composite tape can include directional fibers and/or woven fibers. The fibers may include for example carbon, aramid, fiberglass, aluminum or titanium. 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.
Additional layers can also be included in the reinforced pipe 10. As shown in
In a first embodiment, illustrated in
Referring now to
A third embodiment of the pipe is illustrated in
A fourth embodiment of the pipe is illustrated in
The intermediate layer 16 may be a TPC, for example, similar to the reinforcing layer 14. In the first and second embodiments, the intermediate layer may include generally unidirectional fibers (e.g. fiberglass) within a thermoplastic.
Referring now to the flow chart of
At step 52, a longitudinal reinforcement layer is applied to the outer surface of the formed tubular member. As an alternative or a supplement, the reinforcement layer may be placed within the wall of the tubular member during the extrusion step 50. The longitudinal reinforcement layer may be a TPC tape applied in strips that are oriented parallel to a longitudinal axis of the preform. 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.
A radial reinforcement layer is wrapped around the intermediate layer and tubular member at step 54. The two 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.
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.
Referring now to the flow chart of
At step 64 a radial reinforcing layer is wrapped around the tubular member. The two reinforcing layers may be made of substantially the same or similar material to that of the tubular member. Optionally, the reinforcing layer may be made of a material that is different than that of the tubular member.
Further, once the 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.
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.
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.
