Metal deforming – By tool-couple pressing together adjacent surface portions... – To form helically-seamed tube
Reexamination Certificate
1999-11-17
2001-09-04
Larson, Lowell A. (Department: 3725)
Metal deforming
By tool-couple pressing together adjacent surface portions...
To form helically-seamed tube
C072S379200
Reexamination Certificate
active
06282933
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method of manufacturing a metal carcass for a flexible pipe or umbilical and relates more particularly to the manufacture of a metal strip that can be used to produce a metal carcass.
The flexible pipe to which reference is made in what follows is the pipe used in off-shore oil production and which comprises, from the inside outwards, a metal carcass, an internal sealing sheath, a pressure vault, one or more layers of armour and an external sealing sheath. A flexible pipe of this kind is known to the specialists as a rough-bore flexible pipe as opposed to a so-called smooth-bore flexible pipe wherein the innermost element consists of an internal sealing sheath on which a pressure vault is wound.
These flexible pipes have to exhibit a certain number of mechanical properties particularly collapse strength to allow them to resist collapse which may be brought about by the external pressure, when the flexible pipe is in service, particularly in deep-water applications, and/or the contact pressures exerted on the flexible pipes, particularly during laying and handling. Now, this collapse strength often depends on the mechanical integrity of the metal carcass which, practically alone, has to withstand the force of the external pressure.
The metal carcass is generally made of a profiled strip wound into interlocked turns, for example, an interlocked strip or interlocked shaped wire such as a T-shaped, U-shaped, S-shaped or Z-shaped wire. The shaped strip or wire is wound at an angle in the region of 90°, so that the flexibility of the metal carcass produced is not affected, so as to give the flexible pipe comprising such a metal carcass sufficient flexibility.
This being the case, there are a number of solutions which have been proposed to attempt to improve the collapse strength.
A first solution consists in increasing the thickness of the strip used to produce the metal carcass, but keeping the same S-shaped profile. However, there is an upper limit of the thickness which cannot be exceeded, and of the order of 3 mm. Above this thickness, shaping tools would no longer be able to shape the strip, unless extremely robust tools were made, but this is not economically acceptable. Furthermore, the increase in pipeline weight is not compatible with deep-water applications.
A second solution consists in increasing the height of its carcass while keeping the same profile and the same initial strip thickness. This kind of solution produces a carcass whose weight is equivalent to that of the first solution. This type of carcass is described in EP-0,429,357. Here too, the thickness of the strip which cannot exceed 3 mm proves to be a limiting factor.
A third solution consists in increasing the second moment of area of the profile by simplifying it; to this end, a carcass of the so-called box-section strip has been employed. However, the box-section strip led to an increase in the thickness of the strip and in the volume of the metal carcass and therefore to an increase in the weight of the flexible pipe and in its cost. The box-structure carcass is described in EP-0,494,299.
A fourth solution consists in increasing the yield strength of the strip by using high performance metal alloys such as duplex stainless steels or any other alloy with good mechanical properties (nickel-based alloys). This last solution considerably increases the cost of the metal carcass and therefore of the flexible pipe for certain uses thereof.
A flexible-pipe carcass may deform when a significant load is applied to it, the formation being in two main modes, namely the cardioid mode or the ovalized mode. To prevent ovalization of the carcass from occurring too rapidly, a pressure vault may be used which is dimensioned such that ovalization is delayed for as long as possible. Thus, in practice, and under the conditions of use of the flexible pipe, the metal carcass tends to deform only in cardioid mode.
To improve the performance (collapse strength) of the metal carcass in cardioid mode, it is necessary to improve the mechanical properties of the materials used for the carcass. However, when the mechanical properties of the strip from which the metal carcass is made are improved in a controlled manner, this sometimes results in a strip which can no longer be shaped to a determined profile because it has an insufficient elongation at rupture (A%).
SUMMARY OF THE INVENTION
The object of the present invention is to provide a method of manufacturing a metal carcass so that it has an improved collapse strength without an increase in weight, and for this to be possible irrespective of the metal used to make the strip.
In other words, for the same weight of metal carcass, better collapse strength is achieved. It is possible for this improvement in the mechanical properties to be put to good use in various ways, at the choice of the manufacturer of flexible pipes and/or according to the conditions of use of the flexible pipes.
One subject of the present invention is a method of manufacturing a metal carcass that can be used in a flexible le pipe comprising a pressure vault, in which use is made of a band of metal strip which is shaped and then helically wound to form the said metal carcass which, in cardioid mode, has a given collapse strength, characterized in that the said metal strip is work-hardened prior to shaping to give it elongation at rupture of at least 15%, and in that the said metal carcass which is made from the said work-hardened metal strip has, in cardioid mode, a collapse strength which is at least 15% higher than the said given collapse strength.
One advantage of the present invention lies in the fact that the weight of the metal carcass can be reduced without in any way lowering the collapse strength.
This is because, with a given collapse strength of the metal carcass obtained according to the invention, it is possible to use a flexible pipe either at a greater depth for the same weight of carcass or at a shallower depth but with a lighter carcass. It is generally accepted that the depth at which a flexible pipe can be used depends, in particular, on the collapse strength in cardioid mode of the metal carcass contained within the flexible pipe.
Other advantages and features will emerge clearly from reading the description of a preferred embodiment of the invention.
REFERENCES:
patent: 3958439 (1976-05-01), Kawaguchi et al.
patent: 4854032 (1989-08-01), Dambre
patent: 5666841 (1997-09-01), Seeger et al.
patent: 0429357 (1991-05-01), None
patent: 0494299B1 (1994-06-01), None
patent: 2560608 (1985-09-01), None
patent: 1376266 (1974-12-01), None
patent: 9202751 (1992-02-01), None
patent: 9618060 (1996-06-01), None
BS EN 10088-2 : 1995 “Stainless steels—Part 2. Technical delivery conditions for sheet/plate and strip for general purposes”.
Coflexip
Larson Lowell A.
Ostrolenk Faber Gerb & Soffen, LLP
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