Flexible pipe with an associated end-fitting

An assembly of an end-fitting (9) and a flexible pressure pipe which is of a non-bonded structure and comprises a number of layers including at least one layer having a number of helically wound flat metallic tensile armor wires with end parts which, in the assembled condition, are embedded in an anchor consisting of a casting material such as epoxy which is injected into a cavity formed in the end-fitting. The flat wire end parts have at least one twist turning generally around the centerline of the wire. Said twists lock the tensile armor wires firmly in the anchor and therefore provide a greater resistance to axial tensile loads acting on the assembly than has been known before. Furthermore the joint is a simple and cheap structure and can be made in situ.

BACKGROUND ART
 The invention concerns a flexible pressure pipe with an associated
 end-fitting having an axially extending through opening, where the pipe is
 of a non-bonded structure comprising a number of layers including an
 extruded polymer inner lining extending into the through opening.
 Flexible pressure pipes are used for a variety of applications, including
 water supply lines, sewage lines and lines for transporting chemicals such
 as liquid ammonia and phosphoric acid and also high pressure offshore
 flexible pipes for the oil and gas industry.
 The joint between the inner lining and the end-fitting must be able to
 resist the axial tensile load acting on the inner lining, when the
 flexible pipe is descending over a great length, and also such stresses
 which arise as a consequence of temperature fluctuations.
 Conventionally, said joint is provided by squeezing the inner lining
 between an outer conical ring and an inner conical ring which is pressed
 in between the inner lining and the carcass of the pipe. The effect of
 this squeezing will, however, diminish gradually as the plasticizer
 disappears from the plastic material of the lining.
 Another drawback is that temperature stresses can arise in the joint
 because the plastic material has a high coefficient of expansion.
 In the document GB 891 611 A is described a tamber-proof fitting for
 attachment to the end of a hose having a liner of substantially plastic
 material with a braided covering thereon. By assembling, an end of the
 liner is squeezed between an inner nipple and an outer body member having,
 on the innerside, sharp ribs which by the squeezing is forced into the
 material of the liner forming complementary share grooves in the liner.
 This known technique cannot be used for pipes having an inner carcass
 which not allows the liner to be squeezed and the nipple to be screwed in.
 Furthermore, the share grooves in the liner functions with a dangerous
 notch effect which is not acceptable for high-quality flexible pressure
 pipes exposed to high loads.
 SUMMARY OF THE INVENTION
 The object of the invention is to provide a flexible pressure pipe with an
 associated end-fitting of the type mentioned in the opening paragraph in
 which the joint between the inner lining of the pipe and the end-fitting
 is a simple and cheap structure and provides a greater resistance to axial
 tensile loads acting on the inner lining than has been known before.
 This is achieved in that on the outer surface of the end part of the inner
 lining at least one annular groove is formed, a lock ring is attached to
 the inner lining by means engaging said annular groove, and the lock ring
 is attached to the end-fitting, whereby the inner lining can be firmly
 connected to the end-fitting in a simple and time efficient manner.
 The lock ring can be attached to the annular groove in the inner lining by
 a substantially corresponding annular rib on the inner surface of the lock
 ring. This embodiment is very simple.
 To compensate for inevitable tolerances of the inner lining and in the
 preparation of the joint between the lining and the lock ring, in another
 expedient embodiment the lock ring can be attached to the annular groove
 in the inner lining by a circlip which is fitted into both said annular
 groove in the inner lining and an opposing groove in the inner surface of
 the lock ring.
 A particularly strong connection between the inner lining and the lock ring
 is obtained when the annular groove in the outer surface of the inner
 lining is formed by rolling, such that the material of the lining will be
 strengthened and imparted with a better structure by cold hardening.
 For improving the strength of the joint between the lock ring and the inner
 lining, the annular groove in the outer surface thereof can be formed as a
 segment of circle and the depth of the groove can be between 0.2-0.5 times
 the thickness of the lining.
 The lock ring can easily be mounted on the inner lining when it has a
 transverse slit or consists of two or more sectors of a circle.
 In a particularly advantageous and strong embodiment, the lock ring can be
 fitted into a holding groove formed in the wall of the through opening of
 the end-fitting, and for securing this connection between the lock ring
 and the holding groove there may be a gap filled with a casting material,
 e.g. a polymer such as epoxy.
 The invention also concerns a method for assembling a flexible pressure
 pipe with an associated end-fitting having an axially extending through
 opening, where the pipe is of a non-bonded structure comprising of a
 number of layers including an extruded polymer inner lining extending into
 the through opening. Said method comprises: removing the layers
 surrounding the lining at the end of the pipe, rolling at least one
 annular groove in the outer surface of the end part of the inner lining,
 placing a lock ring consisting of two or more sectors of a circle around
 the end part of the lining such that a rib on the lock ring, or a circlip
 which engages a groove in the lock ring, engages the groove rolled in the
 outer surface of the end part of the lining, securing the lock ring
 sectors, and attaching the lock ring to the end-fitting. The method can
 advantageously be performed in situ.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
 FIG. 1 shows a flexible pressure pipe, which is generally designated by 1.
 The pipe is of a non-bonded structure comprising a number of layers which
 in this embodiment are:
 a carcass 2 of an interlocking structure made from metallic strips. The
 carcass serves, in the main, to prevent collapse of the pipe due to pipe
 decompression, external pressure, tensile armour pressure and mechanical
 crushing loads,
 an inner lining 3 in the form of an extruded polymer layer for providing
 internal fluid integrity,
 a pressure armour 4 in the form of structural layers consisting of
 helically wound C-shaped metallic strips with a high lay angle,
 a tensile armour 5 consisting of a pair of helically counter wound flat
 metallic tensile wires 6 with a lay angle typically between 20.degree. and
 60.degree.. The tensile armour serves to provide resistance to axial
 tensile loads, and
 an outer sheath 7 in the form of an extruded polymer for shielding the
 structural elements of the pipe from the outer environment and providing
 mechanical protection.
 FIG. 2 shows an assembly 8 of an end-fitting 9 and the flexible pressure
 pipe 1. The end-fitting 9 forms the transition between the pipe and the
 connector and for this purpose has a first part 10 with a connection
 flange 11, a second part 12, and a third part 30. The three parts 10; 12;
 30 delimit a cavity 13 which partly is substantially cone-shaped. The
 end-fitting 9 has furthermore a through opening 14 for accommodating an
 end of the pipe 1.
 When assembling the flexible pressure pipe 1 with the end-fitting 9 the
 flat metallic wires 6 of the tensile armour 5 are led into the cavity 13
 in the end-fitting and a casting material, e.g. epoxy, is injected into
 the cavity making an anchoring for the wires.
 The carcass 2 is fastened to the end-fitting 9 by means of a lock nut 15,
 and to the inner lining 3 by means of a lock ring 16 fitting into an
 annular groove 17 in the wall of the through opening 14. The lock ring 16
 is in the embodiment shown secured in the groove 17 by a casting material
 18, e.g. epoxy, which is injected through a hole 19.
 A ring 20 provides a stop for the lock nut 15. In the embodiment shown a
 sealing ring 21 for tightening the end-fitting 9 and the inner lining 3 is
 fitted into a groove 22 in the ring 20.
 After having removed the layers 4, 5, 7 surrounding the lining at the end
 of the pipe, two annular grooves 23 are rolled in the outer surface of the
 end part of the inner lining, whereafter the lock ring 16, which consists
 of one or more sectors of circle, is placed around said end part and
 secured with a clamp 24.
 In the embodiment shown in FIG. 3 two annular ribs 25 are formed on the
 inner surface of the lock ring 26. The ribs 25 correspond to the annular
 grooves 23 rolled in the inner lining 3 and therefore engage these grooves
 firmly.
 FIG. 4 shows another embodiment of a lock ring 27 according to the
 invention. In this case two annular grooves 28 are formed on the inner
 surface of the lock ring 27 and two circlips 29 simultaneously engage the
 grooves 28 formed in the lock ring and the groove 23 rolled in the inner
 lining 3. This construction can advantageously compensate for tolerances
 which are caused by the manufacturing of the inner lining and the lock
 ring.
 Having thus provided a general discussion, and specific illustrations by
 way of examples it is to be understood that no undue restrictions are to
 be imposed by reason thereof. Many other embodiments are imaginable within
 the scope of the invention. The specific locking, according to the
 invention, between the inner lining 3 of the flexible pressure pipe 1 and
 the end-fitting 9 can also be used in combination with other constructions
 of the joint between the end-fitting 9 and the tensile armour wires 6 and
 the carcass 2, respectively, in addition to those described above and
 shown in the figures.