Patent Application
20200021097
This invention relates to a termination assembly for an umbilical, as well as to a method of making a termination assembly for an umbilical.
An umbilical is a type of elongate element used in subsea structures in the oil and gas industry. They are typically used for transmitting power, signals and/or fluids (for example, for fluid injection, hydraulic power, gas release, etc.) to and from a subsea installation. Thus, an umbilical generally comprises a group of one or more types of elongate active elements such as electrical cables, optical fibre cables, steel tubes and/or hoses. These active elements may be cabled together for flexibility, over-sheathed and, when applicable, armoured for mechanical strength. API (American Petroleum Institute) 17E “Specification for Subsea Umbilicals”, fourth edition, April 2011, provides standards for the design and manufacture of such umbilicals.
The point at which an umbilical is connected to another component, for example a subsea installation, is known as an umbilical termination. In use, the axial tensile loads acting on an umbilical can be very high. Thus, a known problem is that the joint between the umbilical termination and the umbilical need to have sufficient strength to withstand such great axial loads acting thereon.
WO 2008/037962 describes one attempt to solve this problem. This document relates to an umbilical termination assembly wherein all or most of the elongate active elements comprising the umbilical are steel tubes. The umbilical termination assembly comprises a cavity through which the steel tubes pass, the cavity being filled with a filler material. In order to help anchor the steel tubes in the filler material, and to assist in resisting tensile loads, one or more areas of increased localised diameter (in the form of washers, sleeves or collars) are provided on the outer surface of the steel tubes.
A similar system involving the use of such areas of increased localised diameter is described in WO 2009/007728. In this document, the filler materials additionally comprise spheroidal beads.
A disadvantage of the umbilical termination assemblies described above is that the washers, sleeves or collars need to be welded onto the steel tubes. The welding step, and subsequent welding qualification, is time consuming. In addition the heat generated can damage the tubes. The welding process normally has to be carried out in a restricted space, meaning that the work needs to be carried out by a highly skilled welder. And also, due to the limited space it is difficult to control weld geometry. The resulting weld is also more sensitive to environment induced cracking, such as hydrogen induced stress cracking (HISC), due to the introduction of residual stress and the lack of a uniform microstructure in the weld. This invention seeks to overcome the problems caused by welding the washer, sleeve or collar onto the steel tube.
According to one aspect of the invention, there is provided a termination assembly for an umbilical comprising a chamber through which pass one or more tubes extending from the umbilical, the chamber containing a filler material, wherein at least one tube is provided with an anchor for securing the at least one tube in the filler material, the anchor comprising a shape memory material.
According to a second aspect of the invention, there is provided a method of making a termination assembly for an umbilical, wherein one or more tubes extend from the umbilical, the method comprising inserting the one or more tubes extending from the umbilical into a chamber within the termination assembly either before or after steps (a)-(c) below, the method comprising the steps of:
This invention will be further described by reference to the following Figures which are not intended to limit the scope of the invention claimed, in which:
It has been found by the inventors that the large change in shape that can be provided by shape memory materials is particularly useful when mounting an anchor on the tube of an umbilical. The use of such materials can avoid the need for welding and make the installation of the anchor onto the tube easier. In the context of the invention, shape memory materials are generally defined as materials which, on the basis of a reversible phase change, induced by a stimulus, can be deformed, and which then return to or towards their original shape when the stimulus ceases. The expression phase change is also known as phase transition. The shape memory material may be an alloy, a polymer, a foam or any shape memory material suitable for the present application. The stimulus may be a change in temperature (cooling, heating), or the application of a magnetic field, an electrical field or any other stimulus, provided that the stimulus leads to a phase change of the shape memory material and allows a change in shape of the shape memory material. For example, the shape memory material may be a shape memory alloy which can be cooled below a temperature of transformation Mf, deformed, and which then returns to or towards its original shape as its temperature increases above a temperature of transformation Af. The tubes of the umbilical are generally made of steel, more particularly duplex steel, even more particularly super duplex steel.
The anchor may comprise an aperture through which the at least one tube passes. The shape memory material may be chosen such that prior to delivering the stimulus it is in a first shape, that the stimulus can be delivered and the material deformed into a second shape which is different from the first shape, and that when the stimulus is ceased it returns to or towards the first shape. When the shape memory material is in the first shape, it may comprise an aperture having a first shape the umbilical tube cannot pass through. In particular, the aperture may have a first size which is too small for the tube to pass through. More particularly, the deformation into the second shape may comprise deforming the aperture to a second shape which the tube can pass through. In particular, the deformation may comprise expanding the aperture from a first size to a second size which the tube can pass through. More particularly, when the shape memory material stimulus is ceased, the shape/size of the aperture may return towards its first shape, or its first size, thereby gripping the tube.
In relation to the invention, the filler material may comprise any such material as is known in the art for filing a chamber/cavity through which umbilical tubing passes, and for example may be selected from the group consisting of epoxy resins and polyester resins. In some embodiments, the chamber is filled or substantially filled with the filler material. In some embodiments, the filler material may comprise additives such as sand or glass beads. These additives can, for example, lower the transition temperature of the filler material.
In some embodiments, the shape memory material is a shape memory alloy. More particularly the shape memory alloy may be a nickel-titanium alloy. A suitable alloy is Nitinol. The shape memory alloy may be chosen such that when it is at room temperature it is in a first shape, that it can be cooled (ie the stimulus) below room temperature and deformed into a second shape which is different from the first shape, and that as it returns to room temperature it returns to or towards the first shape. In particular, the shape memory alloy may be cooled to or below the temperature of transformation Mf which is generally below the lowest operating temperature range of the umbilical. When the shape memory alloy is in the first shape, it may comprise an aperture having a first shape the umbilical tube cannot pass through. In particular, the aperture may have a first size which is too small for the tube to pass through. More particularly, the deformation into the second shape may comprise deforming the aperture to a second shape which the tube can pass through. In particular, the deformation may comprise expanding the aperture from a first size to a second size which the tube can pass through. More particularly, when the shape memory alloy returns to room temperature the shape/size of the aperture may return towards its first shape, or its first size, thereby gripping the tube.
When the shape memory alloy is in the second shape, the shape memory alloy is in the second phase. When the shape memory alloy is in the first shape, the shape memory alloy is in the first phase.
In particular, when the shape memory alloy is in the first shape, or the aperture is in its first shape, it is in an austenitic phase. Preferably, the shape memory alloy is selected such that it converts from an austenitic phase to a martensitic phase at the temperature of transformation Mf which is preferably at a temperature below room temperature, more preferably at a temperature below the lowest operating temperature range of the umbilical. In particular, the shape memory alloy is deformed into the second shape, or the aperture expanded to a second shape, when it is in the martensitic phase. More particularly, the shape memory alloy then returns to or towards the first shape, or the aperture returns to or towards its first shape, when it converts back to the austenitic phase. Thus, in the termination assembly of the invention, the shape memory alloy is generally in the austenitic phase.
The anchor can have a variety of configurations. In particular, it may be formed such that when the material is in its second shape, or the aperture deformed to its second shape, the anchor can slide onto a tube, and that when the material is in (or has returned towards) its first shape, or the aperture is in (or has returned towards) its first shape, it grips the outer surface of the tube. In some embodiments, the anchor may be an annulus, such as a collar, washer or sleeve, a short tube, or a coil. One or more anchors can be mounted on the same tube. One or more anchors can be mounted on more than one tube. In this context, the surface of the anchor which, when the anchor is mounted on a tube, faces towards and/or contacts the tube is referred to as the inner surface. Similarly, the surface of the anchor which, when the anchor is mounted on a tube, faces away from the tube is referred to as the outer surface. Preferably, the surface of the anchor that grips the outer surface of the tubes (generally the inner surface of the anchor) is smooth. In this context, smooth it is to be understood be a roughness of less than 3.2 μm (125 μin). More particularly, the roughness of the surface of the anchor that grips the outer surface of the tubes may be calculated using the Root Mean Square (RMS) method (Rq) or the average method (Ra). The gripping of the anchor around the tube can thus be provided by friction and contact pressure around the tube. In some embodiments, the surface of the anchor that grips the outer surface of the tubes may comprise an indentation. When the anchor is an annulus (in particular, a collar, washer, sleeve or short tube), the indentation may be in the form of an annular groove on the inner surface of the anchor. The indentation can locally plastically deform the tube and assist the mechanical grip of the anchor around the tube.
In a particular embodiment, the anchor is in the form of a collar or disk. The collar may be formed entirely from a shape memory material, more particularly entirely from a shape memory alloy. In its first shape, the collar may be a generally circular tube. More particularly, the collar may have a central generally circular bore (ie the aperture referred to above). In its first shape, the collar may have an internal diameter of around 5-100 mm, more particularly 10-45 mm, even more particularly 10-30 mm and even more particularly 10-20 mm. In particular, in its first shape the collar comprises a wall having a thickness of 0.2-5 mm, more particularly 0.5-2 mm, even more particularly 0.6-1.6 mm. In some embodiments, at least part of the outer surface of the collar is conical. In a particular embodiment, the collar may have a variable thickness and/or a variable internal diameter along its length. For example, the collar may comprise a thicker central section which is sandwiched between two thinner outer sections. The thicker central section may be in the form of a central disk. In some embodiments, there may be more than one thicker central section, each section separated by a thinner linking section. The thinner outer sections may be conical. In particular, their thickness may decrease as they extend away from the thicker central section.
In some embodiments, more than one anchor may be provided on a tube. In some embodiments, the anchor may comprise a non-shape memory material collar sandwiched between two shape memory material collars. More particularly, the anchor may comprise a non-shape memory alloy collar sandwiched between two shape memory alloy collars. The two shape memory material (for example, alloy) collars may be as described above. The non-shape memory material collar may be formed from steel. The non-shape memory material collar may comprise a central generally circular bore. In particular, the bore of the non-shape memory material collar may have a diameter which is larger than an outer diameter of the tube. More particularly, the bore of the non-shape memory material collar may have a diameter such it can be slid onto the tube.
The tube maximum and minimum tolerances are usually governed by ASTM A789 and API 17E. A typical tolerance for the tube's outer diameter is +/−0.13 mm (0.05 inch) on tubes with an outer diameter smaller than 38.1 mm (1.5 inch), and +/−0.25 mm (0.01 inch) for larger diameter tubes.
There is a hoop stress σr within the collar once it is mounted on the tube in the termination assembly. This hoop stress results from the strain resulting from the variation in the diameter (ie the size) of the bore (ie the aperture), and also from the mechanical properties of a shape memory alloy. Surprisingly, it has been found by the inventors the optimum hoop stress for the collar is between 500 MPa and 700 MPa. Such hoop stress within the collar allows to have a suitable gripping of the tube when the collar converts back to the austenitic phase.
As discussed below, the pressure applied by the collar to the tube is preferably between 70 MPa and 100 MPa. Such pressure can help to ensure an efficient anchoring of the collar around the tube without generating plastic deformation of the tube. In an alternative embodiment, the collar can plastically deform the tube. To this end, the inner surface of the collar may comprise an indentation as described above in order to locally plastically deform the tube and thus prevent damage along its length.
In relation to the method of making a termination assembly for an umbilical, the shape memory material may be as described above, and the anchor may be as described above. In some embodiments of the method, step (a) may comprise:
In particular, in step (i), the first shape may be a first size which is too small for the tube to pass through. More particularly, in step (iii) the deforming may comprise expanding the aperture to a second size which is large enough for the tube to pass through. The step (c) of allowing the shape memory material to undergo a phase change in which at least some of the second phase converts to a first phase such that the aperture returns towards its first shape may be the result of ceasing the stimulus either after step (ii), or before, during or after steps (iii) or (b). In a particular embodiment, the shape memory material is a shape memory alloy. In a further particular embodiment step (c) comprises increasing the temperature of the anchor above a temperature of transformation Af such that the shape memory alloy undergoes a phase change in which at least some of the second phase converts to the first phase and the aperture returns towards its first shape, the anchor thereby gripping the tube. In a further particular embodiment, step (ii) comprises cooling the anchor below the temperature of transformation Mf such that the shape memory alloy undergoes a phase change in which at least some of the first phase converts to the second phase. Preferably, above the temperature of transformation Af, the shape memory alloy undergoes a phase change in which at least 50%, preferably at least 80% and even more preferably substantially the entire second phase converts to the first phase. Preferably, below the temperature of transformation Mf the shape memory alloy undergoes a phase change in which at least 50%, preferably at least 80% and even more preferably substantially the entire first phase converts to the second phase.
When the aperture (or bore in the case of the anchor being a collar) is in its first size in step (i), it may have a diameter which is less than that of an outer diameter of the tube onto which it is to be mounted. In particular, in its first size the diameter of the aperture (or bore, d1) is 1-5% less than the outer diameter of the tube (d0), more particularly 2-4% less. Thus, d1 is generally between d0−0.05d0 and d0−0.01d0, more particularly between d0−0.04d0 and d0−0.02d0.
In step (ii), the anchor can be cooled below the temperature of transformation Mf. The cooling can be to a temperature below room temperature (ie between −40° C. and 50° C.), more particularly to a temperature of less than −100° C., for example using liquid nitrogen. In step (c) the anchor can be heated above the temperature of transformation Af. The heating can be to a temperature higher than room temperature. Such temperatures may correspond to the working temperature of the umbilical tubing during use, and may for example be from −10° C. to 120° C., more particularly from −4° C. to 90° C. and even more particularly from 2° C. to 55° C.
The temperature of transformation Mf and Af can be measured by Differential Scanning Calorimetry (DSC).
When the aperture (or bore in the case of the anchor being a collar) has been expanded to its second size in step (iii), for example by using a shaft, it may have a diameter which is greater than that of an outer diameter of the tube onto which it is to be mounted. In particularly, in its second size the diameter of the aperture (or bore, d2) is 1-6% greater than the outer diameter of the tube (d0). Thus, d2 is generally between d0+0.01d0 and d0+0.06d0. When the aperture is in its second size, the collar may be generally circular with the aperture being a central generally circular bore. In consequence the installation can be made easier as the clearance ratio between the outer diameter of the tube and the diameter d2 of the aperture (or bore) is particularly important.
As described above, in step (b) the (or each) anchor is then slid onto the tube onto which it is to be mounted. This step is generally carried out at room temperature, particularly if the shape memory material is a shape memory alloy and the stimulus is a change in temperature.
Once the (or each) anchor is in its final position on the tube, in step (c) the aperture returns towards its first shape or first size. If the shape memory material is a shape memory alloy and the stimulus is a change in temperature, the (or each) anchor is allowed to warm up to a temperature at which the aperture returns towards its first shape or first size as defined above. When the aperture returns towards its first size, this causes the diameter of the aperture (or bore) to reduce from d2 towards d1. As a result of this reduction in diameter, the anchor comes into contact with an outer surface of the tube. Since the aperture (or bore) is attempting to return to a diameter d1 which is less than the outer diameter d0 of the tube, it generally applies a pressure to the tube. This pressure leads to a reduction in the tube's outer diameter of around 0.2% to a reduced outer diameter (d0′). The diameter of the aperture (or bore) is therefore limited by the tube to an intermediate diameter (d1′), which is approximately equal to d0′. It is this pressure that retains the anchor on the tube. When the anchor is a collar, this results in a hoop stress σr in the collar and a radial pressure Pt exerted by the collar on the tube as defined above.
The clearance ratio between the outer diameter of the tube and the diameter of the aperture (or bore) (d0−d1/d0) defined above can generate a suitable contact pressure by the collar onto the tube as defined above. In addition, such clearance ratio results in a hoop stress as defined above which is almost constant and which can enable accurate control of the pressure applied by the collar on the tube.
As described above, the method comprises the step (d) of adding a filler material to the chamber. In some embodiments, step (d) comprises substantially filling the chamber with the filler material. The use of a filler material helps to secure the tube in the chamber. This step may, for example, be carried out under pressure. The filler material is then allowed to cure within the chamber. The filler material may be as described above.
The method according to the invention can, for example, be performed onshore at production facilities during manufacturing operations or offshore during installation.
The invention will now be described in more detail below, in relation to specific examples in which the anchor is a shape memory alloy collar or coil.
Example of Pressure Pt Exerted by the Collar on the Tube
Regarding the pressure Pt applied to the tube, the maximum and minimum pressures that should be applied by the collar to the tube should be determined on the one hand by the mechanical properties of the tube and on the other hand by the axial load that the termination assembly is subjected to.
More particularly, the material used for the tubes may, for example, be a super duplex material, generally a super duplex steel. For example, a duplex stainless steel comprises a mixture of austenitic and ferritic duplex phase structure. A super duplex stainless steel has a Pitting Resistance Equivalent Number (PREN) of >41, where PREN=% Cr+3.3×(% Mo+0.5×% W)+16×% N. Usually, super duplex grades have 25% or more chromium. For such a material, the Yield Strength σy is between 500 MPa and 750 MPa.
To try and keep the deformation of the tube in the elastic domain the pressure Pt should not exceed around 100 MPa. The minimum pressure Pt to be applied to the tube in order to retain the collar on the tube depends upon the axial load F that the tube will have to withstand during operation. The collar in the termination assembly may be strong enough to withstand this axial load. This load in mainly transferred to the termination though the collar and through the locking effect of the collar in the filler material. For example, for axial load of around 17 kN the pressure Pt should be at least around 70 MPa.
Example of Thickness of the Collar
In relation to the thickness of the collar (ie (outer diameter−internal diameter) divided by 2), the inventors carried out several tests to assess the effect of the thickness of the collar (t) on the pressure Pt applied to the tube by the collar depending on the particular hoop stress σr defined above within the collar for shape memory materials. The results seemed to validate Lame's equation which sets the relation between the hoop stress and the pressure as follows:
It can be deduced that the thickness of the collar acts on the pressure Pt applied by the collar onto the tube as follows:
where t is the thickness of the collar, D′ is the mean diameter of the collar once mounted on the tube, and σr is the circumferential stress (hoop stress) in the collar.
The upper and lower limits of the thickness of the collar depend upon the pressure that should be applied to the tube and the allowable compressive strength that the filler material is able to withstand. It has been found by the inventors that the thickness of the collar should be less than 25 mm, preferably between 0.5 mm and 10 mm, more preferably between 0.5 mm and 2 mm, and preferably between 0.7 mm and 1.6 mm. Above such thickness, the pressure Pt could be above the pressure limit and may therefore induce plastic deformation to the tube. Below 0.5 mm, the anchoring of the collar in the filler material may not be enough to lock the collar into the filler material.
As shown above, the thickness of the collar has to be determined in order to limit plastic deformation of the tube and limit damage to the filler material, while providing an efficient anchoring in the filler material. In this context, a solution could comprise providing a collar with a suitable thickness to prevent damage to the tube and increasing the overall area of the collar to achieve the anchoring of the collar into the filler material. To this end, in some embodiments of the termination assembly several collars (at least two, depending on the thickness of each collar) may be mounted on the tube. The axial load will thus be distributed between them. An example if this embodiment is shown in
An alternative embodiment to provide efficient anchoring of the collar in the filler material involves increasing the thickness of the collar. As set out above, a collar having too great a thickness can induce plastic deformation in the tube. One way of achieving this is for the anchor to comprise three collars. Consequently, according to this embodiment, a central collar having a thickness greater than the collar thickness limit defined above may be mounted on the tube in order to achieve the locking effect into the filler material. In order to try and prevent any damage to the tube, the diameter d3 of the bore of the central collar may be higher than the diameter d0′ of the tube. Consequently, the central collar does not apply pressure to the tube. The central collar is maintained on the tube by being sandwiched between two shape memory collars as described herein. Preferably, the thickness of the central collar is greater than the thickness of the shape memory collars. Since the internal diameter d3 of the collar is much higher than the outer diameter d0′ of the tube its installation is made easier and collar can be made of a non-shape memory material, for example steel. The two shape memory collars are mounted as described above, and when their bore returns to its first size they grip the tube and thereby maintain the central steel collar in position on the tube. An example of this embodiment is shown in
To provide easier installation of the collar around the tube, a variant may consist in a single collar having two side sections which grip the tube and a central disk which provides the locking effect in the filler material. Thus, the two side sections may have an internal diameter d0′ as described above and the central disk may have an internal diameter d3 higher than the outer diameter d0′ of the tube and a thickness higher than the thickness of the two side sections. The side sections may have a conical cross-section such that their thickness decreases as they extend away from the central disk. An example of this embodiment is shown in
An anchor 32 in the form of a collar is mounted on each of the tubes 24 in order to secure each tube 24 in the filler material. The anchor 32 is made from a shape memory material as defined above, for example a nickel-titanium alloy.
In
The shape memory alloy from which the anchor 32 is made has a temperature of transformation Mf below room temperature at which the austenitic phase has converted to the martensitic phase.
As a result of the expansion of anchor 32, diameter d2 of bore 32a is larger than outer diameter d0 of tube 24. Thus, the anchor 32 can now be slid onto the tube 24 into order to mount it thereon. Diameter d2 is general around 1-6% greater than diameter d0.
The anchor 32 is then removed from the liquid nitrogen and slid over the tube 24. This would be by moving the anchor 32 to the left from the position shown in
The anchor 32 is moved to its final position mounted on the tube 24 and it is allowed to continue to warm up. The temperature of the anchor 32 increases above the temperature of transformation Af, at which point the shape memory alloy converts back to the initial austenitic phase and attempts to recover its initial shape. In particular, the anchor 32 returns towards having a bore diameter d1 which is less than the outer diameter d0 of the tube 24. Thus, the diameter of bore 32a decreases until it comes into contact with the outer surface of tube 24. In this way, the anchor 32 grips the tube 24.
To enhance the anchoring of the anchor into the filler material while keeping an easy installation and manufacturing process, in an alternative embodiment the anchor may be a coil 332 as shown in
The cross-section of material (eg a shape memory alloy wire) used to make the coil 332 of
Steel retention collar 235 has an internal bore 235a with a diameter d3 which is larger than the outer diameter d0′ of tube 24 and generally larger that the diameter d1′ of the bores 233a, 234a of shape memory alloy collars 233, 234. Thus, for example, in the arrangement shown in
To install the anchor 232 of
Alternatively, and as shown in
A further embodiment of the anchor 432 is shown in
| Number | Date | Country | Kind |
|---|---|---|---|
| 1621513.9 | Dec 2016 | GB | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/IB2017/001667 | 12/7/2017 | WO | 00 |
