Pipes and tubular conduits – Flexible – Spirally wound material
Reexamination Certificate
2000-11-01
2003-02-11
Hook, James (Department: 3752)
Pipes and tubular conduits
Flexible
Spirally wound material
C138S120000, C138S144000, C138S129000, C138S155000, C138S169000
Reexamination Certificate
active
06516833
ABSTRACT:
This invention relates to flexible tubular conduits or pipes, particularly in situations where the conduit needs to withstand relatively high pressures (typically greater than 50×10
5
N/m
2
). In such cases, the conduits are reinforced by helically wound armour which is compliant in flexure, and profiled to allow each subsequent turn to interlock with the previous turn. Generally, the armour is formed from steel or composite strip.
An example of this type of tubular conduit is un-bonded flexible pipe, used in the recovery of offshore hydrocarbon deposits.
FIG. 1
is a schematic illustration of several arrangements of such pipe in use in various dynamic configurations, in which the pipe is being used to connect a sub-sea well to a floating platform. These are the “free hanging” (A), “Steep S” (B), “Lazy S” (C), “Steep Wave” (D), and “Lazy Wave” (E) configurations. Flexible pipes may also be used in static applications (not shown) to connect sub-sea wells to, for example, a manifold, or to tie wells which are several kilometers distant to an existing sub-sea infrastructure. There are of course other applications in addition to the offshore applications mentioned here.
An illustration of a flexible conduit, typically used in offshore applications, is shown in FIG.
2
. It can be seen that successive layers are used, each layer designed to perform a particular function. The innermost layer
1
is usually an interlocking carcass that resists collapse due to external pressure. This is manufactured from a flat strip which is bent into an appropriate shape. The next layer is an inner polymer barrier
2
, which is a fluid retention layer, and seals the well fluids inside the pipe. This is surrounded by an interlocked pressure armour
3
which is designed to resist internal pressure loading. Supported by an (optional) flat profiled spiral armour
4
, the interlocked pressure armour
3
has a shallow helical angle and acts in the manner of hoops around a barrel. A variety of pressure armour
3
profiles exist in the public domain for use in such offshore applications, some of which are shown in FIG.
3
.
The function fulfilled by the layers
1
-
4
are the subjects of the invention described herein. The remaining outer layers
5
,
6
, and
7
, of the pipe shown in
FIG. 2
, are tensile armour wires designed to support axial load, and polymer layers used to prevent wear, or water ingress in the case of the outermost layer
7
.
Flexible pipe manufacture is carried out using a sequence of continuous processes. First, the carcass layer
1
is manufactured for the entire pipe length, which may be as much as several kilometers long. Then, the polymer sealing layer(s)
2
is/are extruded onto the carcass layer
1
and cooled. A polymer tape may also be used in the application of this layer. The pipe is then fed into a winding machine, which is used to apply the armour layer(s)
3
and
4
. This sequence of alternate polymer extrusions (and/or tape laying) and armour winding is continued until the fill pipe structure is built.
The profiled strips making up the armour layers
3
and
4
, are currently manufactured using a wire-drawing process. Strips are produced with a cross-sectional profile consisting of a sequence of lines and arcs. The outer armour layer
4
is generally rectangular in cross section. In contrast, there are a number of, albeit limited, profiles currently available for the inner pressure armour
3
, some of which are shown in FIG.
3
. These are the “Carcass” (A), “Zee” (B), “Tee” (C) and “Cee” (D) profiles, and have been the subject of several published patent applications including W092/00481, W092/02751, and W091/00467. Of these, the Z~shape (B) and the C~shape (D) are most commonly used in current offshore flexible pipes.
For all such profiles in the public domain, the cross-sectional area distribution is currently designed to make the normal second moment of area substantially more than the second moment of area in the bi-normal direction. Typically, the bi-normal second moment of area is currently less than 20% of the normal second moment of area. The terms “normal” and bi-normal” refer to axes particular to the geometry of a helix, and are described in FIG.
4
. In this figure, where OX
3
is the pipe axis and OX
1
and OX
2
are the radial directions, A is the normal (radial) axis, B is the bi-normal (axial) axis and C is the tangential axis of the helix; &agr;° is the helical angle. The application of this helical geometry to a C-shape profile is shown in FIG.
5
. The bi-normal second moment of area, I
B
, is taken about axis B, and the normal second moment of area, I
N
, is taken about axis N. Profiles with such area distributions have limited stress capacity in the radial directions.
In addition to resisting the pressure loading, the structural integrity of the conduit or pipe is maintained by interlocking subsequent turns of pressure armour, for example in the manner shown in FIG.
3
. This mechanism must be applicable to a continuous assembly process during pipe manufacture and, in use, must allow some axial movement and flexural rotation of the structure whilst, at the same time, preventing the existence of excessive gaps in the pressure armour
3
.
For the pressure armour layer
3
, the primary mode of loading is the internal pressure of the fluids flowing, or contained within, the pipe. A second load is applied to the structure in flexure (seen locally as tension or compression in the layer), while axial tension and external pressure are additional loads. It has been established by the inventors that up to 90% of the internal pressure load is dissipated in this pressure armour layer
3
. The stress expected in the layer, as a result of the functional loading, may be calculated and maximum limits set for a safe design. For flexible pipe in offshore applications, these stress limits are currently dictated by the American Petroleum Institute (API) specification
17
J. A substantial reduction in the stresses developed in the pressure armour is the benchmark test that has been used to assess the improvements in the pressure armour layer(s) of this invention. A similar criterion is used to judge the carcass layer
1
, which resists external pressure and prevents collapse of the pipe due to hydrostatic pressure.
The existing profiles, some of which are shown in
FIG. 3
, have reached their technical hard point, or limit of utility. The pressure capability of a given thickness of these armour profiles, for the range of materials typically used, is not sufficient to meet the intense demands of many applications, such as the high temperature and increasingly high pressure offshore environments. Furthermore, concerns about fretting and fatigue means that the connection mechanisms currently employed by these profiles needs to be revised. This is because the point of contact between the turns is also the location of maximum stress in all loading; flexure, tension, and pressure. Furthermore, the existing profiles have substantial gaps (of the order 1-3 mm) between subsequent turns, which are undesirable. To address these concerns, and to enable higher pressure ratings and/or deeper water capability, as well as possible weight reduction benefits, several original profiled components have been developed for such tubular conduits.
Accordingly, the present invention provides a flexible tubular conduit having a reinforced wall structure comprising at least one component wound helically, the component comprising a body having one or more projections on one or both radial sides and a corresponding number of sockets on the opposing radial sides, the projections of one turn of the winding engaging in the sockets of the next turn of the winding, each projection having an enlarged head portion connected to the body by a narrow neck portion, and each socket having an enlarged portion to receive the head portion of the corresponding projection and a narrow opening on which the neck engages to hold the projection captive in the socket, the sockets and projections having dimensi
Burke Raymond Nicholas
Witz Joel Aaron
Hook James
Moser, Patterson & Sheridan L.L.P.
University College London
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