INSTALLATION COMPRISING THE BEND LIMITER

The present invention relates to a bend limiter comprising a tubular wall structure with a hollow through bore adapted for housing a length section of an elongate flexible member to reduce the risk of the elongate flexible member being damaged by undesired bends.

BACKGROUND

Bend limiters for use in combination with flexible offshore pipes are well known in the art and cover both "bend stiffeners" and "bend restrictors".

In the prior art bend limiter has also been applied for preventing overbending of other types of elongate flexible members, such as power cables and umbilicals.

A bend limiter generally has the function of controlling the bending in elongate flexible members, such as flexible subsea members, which may be subjected to varying and often excessive movement as a result of water waves, tides and weather. Bend limiters are often employed in situations where an elongate flexible member has a minimum permissible radius.

The prior art bend limiters may for example consist of a single elastic body moulded in polyurethane and may alternatively comprise an internal reinforcing structure as described in WO 92/12376 or in GB-A-2,291,686. They may also comprise heat-dissipation means, as is recommended in GB-A- 2,291,686.

US2012261017A discloses a stiffening cover with a relatively high flexural modulus for a flexible pipe, where the flexible pipe has been provided with a stiffened length section by applying the stiffening cover to partially or totally surround the pipe in the stiffened length section. This stiffening cover is simple to mount on production site of the flexible pipe, however, it only provides a limited stiffening effect, which often may not be sufficient. GB 2,304,393 A discloses a bend limiter for cables and hoses comprising a tubular body, which has one or more lines of profiled slotting dividing the tubular body into sections. The slotting has a width which allows the sections to move relative to each other. The slotting is provided in a meander shaped pattern, which provides an interlocking effect. Although the bend limiter functions well for some application, this bend limiter has shown to work only where force impacts are relatively low, and it allows only rather low bends, which for some applications is undesired and/or which result in the bend limiter being exposed to very high forces, which may be detrimental to the bend limiter structure, e.g. by inducing cracks, or cause seizing by tearing interlocked parts partly from each other, which may cause the bend limiter to freeze in a bended position.

DISCLOSURE OF INVENTION

An object of the present invention is to provide a bend limiter, which may be produced with a desired bendability along its length in a relative cost effective way.

In an embodiment, it is an object to provide a bend limiter, which may be shaped to have a desired bendability along its length, which may include bends with a desired bending radius, which bending radius may be relatively low.

In an embodiment, it is an object to provide a bend limiter, which is less vulnerable to seizing and having an excellent service-time.

In an embodiment, it is an object to provide a bend limiter, which is relatively simple to produce and at adequate cost.

In an embodiment, it is an object to provide a method of producing the bend limiter, which is relatively simple and cost effective. In an embodiment, it is an object to provide an installation, which is relatively simple to provide and wherein the installation comprises a bend limiter ensuring a desired and stable bend limiting effect of an elongate flexible member of the installation.

These and other objects have been solved by the invention or embodiments thereof as defined in the claims or as described herein below.

It has been found that the invention or embodiments thereof have a number of additional advantages, which will be clear to the skilled person from the following description.

The inventors of the present invention has found that by providing the bend limiter with one or more cutout sections forming windows as defined in the claims and as described in further details below, the bend limiter may be provided to allow minimum bending radius (MBR) with a relatively large range of selected MBRs, thereby the bend limiter may be designed with an increased flexibility. In addition, the bend limiter may be provided in a very cost effective way.

Further, it has shown that even where a relatively low MBR is required, the bend limiter has an excellent and desired long service time.

It should be emphasized that the term "comprises/comprising" when used herein is to be interpreted as an open term, i.e. it should be taken to specify the presence of specifically stated feature(s), such as element(s), unit(s), integer(s), step(s) component(s) and combination(s) thereof, but does not preclude the presence or addition of one or more other stated features.

Throughout the description or claims, the singular encompasses the plural unless otherwise specified or required by the context.

The "an embodiment" should be interpreted to include examples of the invention comprising the feature(s) of the mentioned embodiment. The term "about" is generally used to include what is within measurement uncertainties. When used in ranges, the term "about" should herein be taken to mean that what is within measurement uncertainties is included in the range.

The term "substantially" should herein be taken to mean that ordinary product variances and tolerances are comprised. All features of the invention and embodiments of the invention as described herein, including ranges and preferred ranges, may be combined in various ways within the scope of the invention, unless there are specific reasons not to combine such features.

Any chemical or physical property is to be determined at standard conditions of 23°C and 1 atm. unless otherwise specified.

The bend limiter, which may be suitable for housing and protecting an elongate flexible member against undesired bends, comprises a tubular wall structure having a length and a hollow through bore with a center axis and an inner diameter D. The inner diameter may for many applications be constant along the length of the tubular wall structure. However, for some applications the inner diameter D of the tubular wall structure may differ along its length. For reducing wear, it may be desired that the inner diameter D of the tubular wall structure is not too much larger than the elongate flexible member is adapted to protect. Therefore, the inner diameter D may conveniently be between the diameter of the elongate flexible member is designed to house to twice the diameter of the elongate flexible member is designed to house, such as from 1 cm larger than the diameter of the elongate flexible member is designed to house to 0.5 m, e.g. to 20 cm or 10 cm larger than the diameter of the elongate flexible member is designed to house.

The tubular wall structure comprises a cut pattern provided along a profiled line. The profiled line extends having a length extending at least in the circumference of the tubular wall structure i.e. at least one lap around the hollow through bore the cut pattern along the profiled line comprises slit sections and cutout sections along the length of the profiled line providing that the cut pattern forms protrusions interlocking with each other. Each protrusion has a stem and a head with a top face facing away from the stem and wherein one or more cutout sections form windows, which border on the stem or on the head face of each of the protrusions. As further described below the cut pattern provided along the profiled line may comprise one or more weak links in the form of short non-through cut length sections along the profiled line, wherein the weak links are adapted to rupture when the bend limiter is in use. These weak links may in particular be beneficial during the production and/or installation of the bend limiter.

In an embodiment, one or more of the interlocked protrusions comprises a cutout section bordering on the stem and a cutout section bordering on the top surface.

The height of the stem and the head, respectively, is determined along the center axis of the stem, and likewise the width of respectively the head and the stem is determined perpendicular to the center axis of the stem.

The term "height" and "lengths" are used interchangeable in respect of the stems, heads and windows.

The head top face may in principle have any shape such as, flat, convex, concave or any combinations thereof. Advantageously, the head top face is flat or convex, preferably with a convex radius that is at least twice the average head height, such as at least 3 times the average head height. It has been found that where the top surface is convex with a convex radius that is relatively large, such as at least twice the average head height, the strength of the interlocked protrusions becomes very high and thereby, the risk of damaging the interlocked protrusions during use even when subjected to high force impacts may be even more reduced. Advantageously, the cut pattern along the profiled line has a meandering shape forming the protrusions as consecutive protrusions along the length of the line, wherein the stem of every second of the protrusions, referred to as first type protrusions are protruding in a first direction and wherein the stem of every other second of the protrusions, referred to as second type protrusions are protruding in a second preferably opposite direction, such that the each of the first type protrusions are interlocking with at least one of the second type protrusions. Except for interlocked protrusions located at respective ends of the profiled line, each of the first type protrusions are advantageously interlocked with two of the second type protrusions and each of the second type protrusions are advantageously interlocked with two of the first type protrusions.

When the bend limiter is in straight and unloaded condition, the interlocked protrusions are advantageously protruding in wall plan, i.e. substantially not protruding into the hollow through bore of the tubular wall structure or protruding outwards away from the center axis of the hollow through bore.

In an embodiment, the at least one profiled line has a slit line width along parts of its length providing said slit sections and a cutout line width along other parts of its length providing said cutout sections, wherein said cutout line width is at least twice the slit line width, such as at least 5 times larger than the line width as said slit sections.

It has been found that due to the cutout sections also referred to as windows, the slit line width may be very narrow, such as 2 mm or less or even 1 mm or less while the windows ensured the desired flexibi lity/bendabil ity of the bend limiter. Due to such narrow slit lines the production of the bend limiter may be performed practically using any cutting tool, even laser cutting while cutting only once when preparing slit lines. This will be described further below. In an embodiment, the stem and head of each protrusion forms a recess which is engaged with at least one recess formed by a stem and head of at least one other of the protrusions to thereby provide the interlocking. The respective interlocked protrusions may advantageously be interlocked with adjacent interlocked protrusions provided along the same - and thereby common - profiled line.

Advantageously, the interlocked protrusions are displaceable in a direction corresponding to a protruding axis of the stems, i.e. along the center axis of the stem. Thereby, the length of the bend limiter and the tubular wall structure may be extended and reduced between a minimum length and a maximum length.

This extension/reduction may be effected locally, thereby providing that the minimum bending radius and thus the flexibility may be improved to a desired level by selecting the height of the windows and thereby the displacement length. Thus, where the bend limiter is bent, the inward curving side of the tubular wall structure is shorter than the opposite outwards curving side of the tubular wall structure. Thus, by providing that the interlocked protrusions are displaceable, the risk of damaging the bend limiter is highly reduced.

In addition, the displacement length of the interlocked protrusions may be selected to vary along the length of the bend limiter and/or along the circumference of the bend limiter, thereby providing a bend limiter structure, which may be customized to any selected use. For example, the bend limiter may be provided to have a first length section with a relatively high stiffness (low flexibility and large MBR) and a second length section with a relatively low stiffness (high flexibility and small MBR).

The protruding axis may be described as an axis of the first and second opposite directions. The protruding axis may advantageously be relatively close to the center axis of the tubular wall structure, such as with an angle between the protruding axis and the center axis of the tubular wall structure of up to 20°, such as up to 15°, such as up to 10°, such as from 2° to 6°.

In an embodiment, the protruding axis of the respective protrusions is perpendicular to the pitch of the cut patterns as defined below or up to 5° from perpendicular to the pitch.

The displacement length between two adjacent protrusions may advantageously correspond to a maximal height determined in the protruding direction of the respective windows which border on the respective top faces of the two adjacent protrusions.

Where the cut pattern comprises one or more weak links, such weak links are ruptured before determining the displacement and/or they are ruptured by performing the displacement or by the displacement.

In an embodiment, the interlocked protrusions are displaceable in a direction corresponding to a protruding axis of the stems, wherein the bend limiter has a first short stage where the interlocked protrusions are in a first displaced stage and a second long stage where the protrusions are in a second displaced stage, wherein the windows in the first displaced stage primarily are located to border on the stems of the protrusions and wherein the windows in the second displaced stage primarily are located to border on the head face of the protrusions.

Thereby, by displacing the interlocked protrusions, the windows are fully or partly transferred between windows that border on the stems of the protrusions and windows that border on the head top face of the protrusions.

The displacement length may be selected by selecting the height of the cutout sections providing the window. The cutout line of the cutout section is the same as the height of the cutout sections. The height of the window conveniently corresponds to the cutout width of the cutout section providing the window.

The window advantageously has a total window area which differs from a minimum total window area to a maximum total window area. At the minimum total window area, the interlocked protrusions are the first displaced stage and preferably, at least 60%, such as at least 80%, such as at least 90% such as the entire of the total window area is provided by windows located to border on the stem of the protrusions. At the maximum total window area, the interlocked protrusions are the second displaced stage and preferably, at least 60%, such as at least 80%, such as at least 90% such as the entire of the total window area is provided by windows located to border on head face of the protrusions.

Where the windows are located to border on the respective stems the windows advantageously are located to also border on a rear face of the respective heads, wherein the rear face of each head is opposite to the top face.

To provide a safe engagement and thereby interlocking, each of the windows when located to border on the stem of one or two of the protrusions independently of each other has a width which is from 0.2 to 1 times the difference between the width of the head and the width of the stem of the protrusion.

In an embodiment, the protrusion has a T shape, where the horizontal bar represents the head and the vertical bar represents the stem. In this embodiment it is desired that the two windows, at least when the interlocked protrusions are the first displaced stage, located on respective sides of the stem have each a width from 0.2 to 0.5 times the difference between the width of the head and the width of the stem of the protrusion, such as a width from 0.4 to 0.49 times the difference between the width of the head and the width of the stem of the protrusion. The height of the two windows located on respective sides of the stem determined when the interlocked protrusions are the first displaced stage are advantageously, substantially equal. The height may differ between the two windows; however, the height of the window with the shortest height may limit the displacement length.

In an embodiment, the protrusion has an L shape, where the horizontal bar represents the head and the vertical bar represents the stem. In this embodiment it is desired that the (single) window, at least when the interlocked protrusions are the first displaced stage, located to border on the stem has a width from 0.4 to 1 time the difference between the width of the head and the width of the stem of the protrusion, such as a width from 0.8 to 0.99 times the difference between the width of the head and the width of the stem of the protrusion.

In an embodiment, each of the windows has a maximal height, which is equal or differs up to 20%, such as up to 10%, such as up to 5%, such as up to 2% from the average maximal heights of the windows. For the most effective use of the windows area, the windows are advantageously substantially of equal maximum height. The maximum height of windows which border on stems is determined when the interlocked protrusions are the first displaced stage and the maximum height of windows, which border on head faces is determined when the interlocked protrusions are the second displaced stage.

In an embodiment, each of the interlocked protrusions have a protrusion length L determined in the protruding direction between a lowermost point of the stem to a furthest protruding point of the head face, wherein the protrusion length L of the respective interlocked protrusions are equal or differs up to 20%, such as up to 10%, such as up to 5%, such as up to 2% from the average protrusion length L of the respective interlocked protrusions.

In an embodiment, the interlocked protrusions in a first length section of the tubular wall structure have a first protrusion length Li and the interlocked protrusions in a second length section of the tubular wall structure have a second protrusion length L2, wherein the first protrusion length Li differs from the second protrusion length L2, e.g. Li> L2, thereby providing a larger flexibility in one of the first and the second length sections of the tubular wall structure than in the other one of the first and the second length sections of the tubular wall structure.

In an embodiment, the stem and head of each of the interlocked protrusions has a stem height and a head height determined along the protruding axis of the stem, wherein the stem height is larger than the head height e.g. up to 500% larger. Preferably, the stem height is from 10% to 300% larger, such as from 25% to 100% larger than the head height.

Where the stem height is varying along its width the average stem height of the stem is applied.

Where the head height is varying along its width the average head height of the stem is applied.

In an embodiment, the stem and head of each of the interlocked protrusions has a stem width and a head width determined perpendicular to the protruding axis of the stem, wherein the stem width and a head width of the respective interlocked protrusions, independently of each other are equal or differ up to 20%, such as up to 10%, such as up to 5%, such as up to 2% from, respectively, the average stem width and the average head width of the interlocked protrusions.

In an embodiment, the stem of the respective interlocked protrusions has a first edge side with a first stem side length and a second edge side with a second stem side length, wherein the first stem side length and the second stem side length are equal or differ up to 5%, such as up to 2% from the average of the first stem side length and the second stem side length. Where the first stem side length and the second stem side length differs, the stem height is determined as the average of the first stem side length and the second stem side length.

The first edge side and the second edge side may be offset in a direction parallel to the stem axis caused by the pitch of the profiled line relative to the center axis pf the tubular wall structure.

In an embodiment, the stem of one or more of the respective interlocked protrusions has a first edge side with a first stem side length and a second edge side with a second stem side length, wherein the first stem side length is at least 5% longer than the second stem side length, optionally the first stem side length is from 10% to 200% longer than the second stem side length, such as from 20% to 100% longer than the second stem side length, such as from 30% to 50% longer than the second stem side length. The one or more stems with relatively large differences between first stem side length and second stem side length may e.g. form part of transition protrusions where the protrusion structure/shape is changing e.g. a change of window heights.

In an embodiment, the stems of the first type protrusions have a first stem height and the stems of the second type protrusions have a second stem height different from the first stem height.

In an embodiment, the heads of the first type protrusions have a first head height, and the heads of the second type protrusions have a second head height different from the first head height.

In an embodiment, the heads of the first type protrusions have a first head width and the heads of the second type protrusions have a second head width different from the first head width.

In an embodiment, the stem of the respective interlocked protrusions has a width which is equal along its height extension or which differs up to 20%, such as up to 10%, such as up to 5%, such as up to 2% from the width of the average stem width.

As described above, the head conveniently has a width that is larger than the width of the stem to provide a desired engagement. Preferably, the width of the head is at least 10% wider than the width of the stem, such as at least 20% larger, such as at least 30% larger than the width of the stem, more preferably the width of the head is from 115% to 300% the width of the stem, such as from 120% to 200%, such as from 125% to 150 the width of the stem.

In an embodiment, the head extends beyond the width of the stem at a first side of the stem, but not beyond a second opposite side of the stem, thereby forming an L shape as described above.

In an embodiment, the head extends beyond the width of the stem at both a first and as second opposite sides of the stem, thereby forming a T shape as described above.

Advantageously, the at least one profiled line is a helically meandering profiled line with amplitudes forming the protrusions, the helically meandering profiled line has a pitch relative to the central axis of the tubular wall structure which is up to 20 degrees, such as from 1 to 15 degrees, such as from 3 to 15 degrees.

The pitch is determined by a pitch line crossing through the windows that border on the stem when the interlocked protrusions are in the first displaced stage, i.e. the bend limiter is in its first short stage.

The pitch may vary along the length of the tubular wall structure. In an embodiment, the pitch is substantially constant along the length of the tubular wall structure. In an embodiment, the tubular wall structure comprises two or more cut pattern length sections along its length where the pitch of the respective cut pattern may be equal or may differ.

In an embodiment, the tubular wall structure comprises a plurality of profiled lines, at least one of the profiled lines is a closed line i.e. a line forming a closed circle, such that without weak link or with optional weak link ruptured, the tubular wall structure are cut in two sections along the profiled line and are interconnected by the interlocked protrusions. In this embodiment, the pitch may be 0°.

In an embodiment, cut pattern provided along the profiled line comprises the one or more weak links in the form of short non-through cut length sections along the profiled line as described above. The weak links advantageously have a length along the profiled line, which is 10 mm or less, such as 5 mm or less, such as 2 mm or less.

The weak link advantageously is sufficiently strong to not rupture when the bend limiter is in straight and unloaded condition, whereas the weak link is sufficiently easy to rupture by providing that the bend limiter is subjected to bends. For example, coiling the bend limiter on a reel may rupture at least some of the weak links and in use, the weak links should be sufficiently weak to rupture when subjected to any tensile load.

Advantageously, cut pattern provided along the profiled line comprises the one or more weak links in the form of short non-through cut length sections along the profiled line, wherein the weak links have depressions along its length, such as precuts that are nut cutting fully through the tubular wall structure.

In an embodiment, the cut pattern provided along the profiled line comprises the one or more weak links in the form of short non-through cut length sections along the profiled line, and wherein the weak links are sufficiently weak to rupture by tensile stress caused by bending the bend limiter without thereby providing plastic deformations of the bend limiter other than the weak link rupture.

Advantageously, the profiled line along which the cut pattern is provided extends in a plurality of laps in the circumference of the tubular wall structure, such as at least 5 laps, such as at least 10 laps, such as up to 100 laps, such as up to 50 laps.

A lap in the circumference of the tubular wall structure is herein used to mean one time along the entire circumference of the tubular wall.

In an embodiment, the profiled line extends helically, e.g. determined along the pitch line as defined above, along the length of the tubular wall structure to provide the plurality of laps.

In an embodiment, the profiled line along which the cut pattern is provided, extends in a cut pattern length section of the tubular wall determined along the center axis of the tubular wall of at least 0.5 m, preferably from 1 to 25 m, such as from 2 to 10 m, such as from 3 to 6 m.

In an embodiment, the tubular wall structure comprises two or more cut patterns provided along respective profiled lines extending at least in the circumference of the tubular wall structure and providing respective cut pattern length sections. The respective profiled lines extends in respective cut patterned length sections of the tubular wall. The tubular wall structure may advantageously have an intermediate length between the respective cut patterned length sections. The intermediate length section preferably has an intermediate length section length along the center axis, which may be shorter than the average length of the respective cut pattern length sections.

The intermediate length section may conveniently be free of cut pattern.

The intermediate length section may conveniently comprise a sacrificial anode. For protecting the bend limiter and/or an elongate flexible member housed in the bend limiter against undesired corrosion. The tubular wall structure has an axial length of from 1 to 50 m, such as from 2 to 25 m. For some applications, a very short bend limiter may be sufficient, whereas for other bend limiter it is desired that the bend limiter may be longer. The length of the bend limiter is determined with the interlocked protrusions in the first displaced stage.

In an embodiment, the tubular wall structure comprises two or more cut pattern length sections separated by intermediate length sections, wherein the total lengths of the cut pattern length sections constitutes at least 60% of the axial length of the tubular wall structure, such as from 75 to 95% of the tubular wall structure.

The tubular wall structure conveniently comprises a metallic material, preferably selected from steel, stainless steel, copper, or nickel alloys. Preferably, the tubular wall structure comprises at least a layer of the metallic material, optionally the tubular wall structure consists of the metallic material.

In an embodiment, the tubular wall structure comprises an internal wear coating.

The internal wear coating may e.g. be an anti-friction and/or bearing coating. The wear coating may for example be a polymer or a polymer containing composition, such as a coating comprising one or more of polyethylene (PE), polyurethane (PU), polyetheretherketone (PEEK), polytetrafluoroethylene (PTFE) or polyvinylidene fluoride (PVDF), e.g. in a thickness of from 5 pm to 5 mm, such as from 10 pm to 1 mm, such as from 25 pm to 0.1 mm.

The wear coating is advantageously sprayed or painted on the internal side of the tubular wall structure. In an embodiment, the wear coating is of a thermoplastic polymer and the coating is applied as a liner, e.g. by inserting a tube of the thermoplastic polymer into the tubular wall structure, applying a pressure in the tube and heating the thermoplastic polymer to provide that it adheres to the internal surface og the tubular wall structure. This lining is preferably performed prior to providing the cut pattern(s). To provide a desired strength, the tubular wall structure may have a wall thickness in the range of from 1 to 80 mm, such as in the range of from 3 to 50 mm, conveniently in the range of from 5 to 30 mm. The wall thickness may be equal along its length or it may differ along its length e.g. for providing a length section with a higher weight and another length section with a lower weight.

The tubular wall structure hollow through bore may for example have a diameter D of from 0.1 to 1.4 m, such as from of 0.2 to 1.2 m, conveniently in the range of from 0.2 to 1.0 m.

The bend limiter of the invention may in an embodiment be applied in an installation for protecting an elongate flexible member against undesired bends. The bend limiter may e.g. be applied for housing a section of a flexible offshore pipe. Flexible offshore pipes are for example used in the oil industry for raising or transporting hydrocarbons from a subsea wellhead to a platform or floating equipment such as a Floating Production and Storage Offloading vessel known by the abbreviation FPSO. Such flexible pipes are for example described in "Recommended Practice for Flexible Pipe "API Recommended Practice 17 B", fourth edition 2008 published by the American Petroleum Institute. A bend limiter is in particular useful in combination with an unbonded flexible pipe e.g. as described in "Specification for unbonded flexible pipe" API 17J, third edition 2008, also published by the American Petroleum Institute.

In an embodiment, the bend limiter is applied in an installation comprising an elongate flexible member installed in a subsea structure, such as a monopile comprising an installation system as described in DK PA 2021 00156.

The invention also comprises a flexible member installation comprising an elongate flexible member and at least one bend limiter as described above e.g. in the form of the installations mentioned above. The flexible member is located at least partly in the hollow through bore to provide that the tubular wall structure surround the elongate flexible member. This is also described as the elongate flexible member being housed in the bend limiter.

The installation is advantageously an offshore subsea installation comprising at least a length section such as at least 90% of the length, such as the entire of the bend limiter under water.

In an embodiment, the elongate flexible member is a flexible pipe, a power cable or an umbilical.

In an embodiment, the bend limiter is at least temporarily fixed to the elongate flexible member.

In an embodiment, the bend limiter is at least temporarily fixed to or retained in a subsea structure or a sea surface structure.

The invention also comprises a method for producing the bend limiter described above.

The method comprises

• providing a length of a tubular wall defining a hollow through bore and having a diameter D (internal diameter);

• providing a cut pattern in the tubular wall to form the tubular wall structure.

As described above the bend limiter has the further advantage that it may be relatively simple to produce.

The provision of the cut pattern comprises providing the cut pattern to have slit sections and cutout sections along a profiled line having a length extending at least in the circumference of the tubular wall structure to provide that the cut pattern along the profiled lines form protrusions interlocking with each other. The cut pattern, the interlocked protrusions, the windows as well as the sizes thereof may be as described above.

Advantageously, the method comprises providing the cut pattern provided along the profiled line to comprise one or more weak links in the form of short non-through cut length sections along the profiled line, wherein the weak links are adapted to rupture when the bend limiter is in use. Such weak links are very advantageous during the production as they hold the tubular wall structure under high control to ensure that the cut pattern is provided with a desired accuracy. The weak links may also increase safety for the workers during the production, since undesired/uncontrolled bends of the tubular wall structure during the production may be avoided in a relatively simple way.

The method preferably comprises providing the windows to be located to border on the respective stem to provide that one or two window(s) is/are located to border each stem. Thus, at the cutting stage the window are advantageously provided to border on the respective stems, whereas the head faces are advantageously provided by slit sections along the profiled line.

Thereby a very simply and highly controlled cutting procedure may be provided.

In an embodiment, the method comprises providing the interlocked protrusions to be displaceable in a direction corresponding to a protruding axis of the stems, wherein the bend limiter has a first short stage where the interlocked protrusions are in a first displaced stage and a second long stage where the protrusions are in a second displaced stage, wherein the provision of the cut pattern is provided with the bend limiter in its first short stage, wherein the length of the first short stage preferably corresponds to or is identical to the length of the tubular wall without any cuts. In an embodiment, the method of providing the cut pattern along the profiled line comprises slit cutting along the profiled line to a selected location of a cutout section, cutting out the cutout section and continuing slit cutting along the profiled line and repeating until the cut pattern is provided, wherein the slit cutting optionally comprises short non-through cut length sections along the profiled line for the provision of the weak links.

For providing an effective cutting of the cut out section it is desired that the cutting out of the respective cutout section comprises from an end point of the cut slit cutting along a first periphery line forming the cutout section to a turning point and cutting a cross cut back to the or immediately adjacent to the end point of the cut slit and cutting along a second opposite periphery line forming the cutout section to or immediately adjacent to the turning point.

Thereby, the cutting process may avoid re-cutting in an already a cut track.

Re-cutting in a cut track may for some cutting process disturb or even damage the cut track.

The cut pattern may for example be provided using one or more of laser cutting, water jet cutting, plasma cutting and/or oxyfuel cutting.

Preferably, the cut pattern is provided using laser cutting. Laser cutting is a highly effective cutting method; however, the cutting tracks provided are relatively narrow. However, for the present invention the slot cut may conveniently be narrow cuts as described above, and the cutout sections may also be provided by laser cutting e.g. as described above.

All features of the inventions and embodiments of the invention as described herein including ranges and preferred ranges may be combined in various ways within the scope of the invention, unless there are specific reasons not to combine such features. BRIEF DESCRIPTION OF PREFERRED EMBODIMENTS AND ELEMENTS OF

THE INVENTION

The above and/or additional objects, features and advantages of the present invention will be further elucidated by the following illustrative and nonlimiting description of embodiments of the present invention, with reference to the appended drawings.

The figures are schematic and are not drawn to scale and may be simplified for clarity. Throughout, the same reference numerals are used for identical or corresponding parts.

Figure 1 is a side view of a section of a bend limiter of an embodiment of the invention.

Figure 2 is a side view of a section of a bend limiter of another embodiment of the invention.

Figure 3 is a side view of a section of a bend limiter of a further embodiment of the invention.

Figure 4 illustrates a portion of a first example of a cut pattern in a tubular wall structure of a bend limiter of an embodiment of the invention.

Figure 5 illustrates a portion of a second example of a cut pattern in a tubular wall structure of a bend limiter of an embodiment of the invention.

Figure 6 illustrates a portion of a third example of a cut pattern in a tubular wall structure of a bend limiter of an embodiment of the invention.

Figure 7 illustrates a portion of a fourth example of a cut pattern in a tubular wall structure of a bend limiter of an embodiment of the invention.

Figure 8 is a schematic view of a flexible member installation of an embodiment of the invention. Figure 9 is a schematic view of a flexible member installation of another embodiment of the invention.

Figure 10 is a schematic view of a flexible member installation of a further embodiment of the invention.

The bend limiter shown in figure 1 comprises a tubular wall structure 1 with a not shown center axis. The tubular wall structure 1 comprises a cut pattern 2, 3 provided along a profiled line having a length extending at least in the circumference of the tubular wall structure 1. The cut pattern comprises slit sections 3 and cutout sections 2 along its length. The cut pattern 2, 3 is provided along the profiled line to form protrusions 4, 5 interlocking with each other. Each protrusion having a stem 6 and a head 7 with a top face 7a facing away from the stem and wherein one or more cutout sections 2 form windows which border on the stem 6 or on the head face of each of the protrusions 4, 5. As can be seen, the cutout sections 2 has cutout line widths which are much larger than the slit line width of the slit sections, e.g. as described above.

The cut pattern 2, 3 along the profiled line has a meandering shape forming the protrusions 4, 5 as consecutive protrusions 4, 5 along the length of the profiled line. The stem 6 of every second of the protrusions, referred to as first type protrusions 4 are protruding in a first direction and the stem 6 of every other second of the protrusions, referred to as second type protrusions

5 are protruding in a second opposite direction to provide that the each of the first type protrusions 4 are interlocking with at least one of the second type protrusions 4.

The stem 6 and head 7 of each protrusion 4,5 forms at least one and in this example 2 recesses R which are engaged with recesses R formed by the stem

6 and head 7 of adjacent protrusions 4, 5 to thereby provide the interlocking.

In the view that is shown of the embodiment of figure 1, cutout sections 2 (also referred to as windows) are located to border on the stems 6 of the protrusions 4, 5. The bend limiter is now in its first short stage. The interlocked protrusions 4, 5 are displaceable in a direction corresponding to a protruding axis A of the stems 6 from its first short stage to a second displaced stage wherein the windows 2 in the second displaced stage are located to border on the head face 7a of the protrusions. In that way the bend limiter may be provided with a desired flexibility and bendability. As explained elsewhere herein, the cut pattern may be provided in a very cost effective way.

To compensate for the pitch P of the helically meandering profiled line of the cut pattern 2, 3, the protrusions 4, 5 provided by the helically meandering profiled line of the cut pattern 2, 3 are staggered to provide that the stem axis A is substantially parallel to the center axis of the tubular wall structure, such as within an angle to the center axis of the tubular wall structure of up to 5° such as preferably parallel to the center axis of the tubular wall structure.

Thereby, the displacement between the first short stage and the second displaced stage is provided substantially or fully in the direction of the center axis of the tubular wall.

The stem axis A may conveniently have an angle to the pitch P of up to 20 degrees, such as from 1 to 15 degrees, such as from 3 to 15 degrees.

In the embodiment of figure 1, the head 7 is a T shaped head, wherein the head extends beyond the width of the stem at both a first and as second opposite sides of the stem, thereby forming the T shape. To provide that the head face 7a is perpendicular to the center axis of the tubular wall structure, the head has a first height determined in the direction parallel to the stem axis A in a first head width section 7b extending beyond one side of the stem and a second smaller height in a second head width section 7c extending beyond one side of the stem. In a variation thereof, the head face 7a is substantially parallel with the pitch, and the head may have same height in its entire width.

The bend limiter in figure 2 differs from the bend limiter of figure 1 in that the pitch P is smaller and the width 7w of the head 7 relative to the width 6w of the stem 6 is smaller. Thereby, the width sections of the head extending beyond the stem at its respective sides is smaller than in the embodiment of figure 1.

Due to the smaller pitch P in the embodiment of figure 2, the difference between the height 7d of the first head width section 7b and the height 7e of the second head width section 7c is smaller than in the embodiment of figure 1.

The bend limiter in the embodiment of figure 3 is illustrated in its second displaced stage where the windows 12 are located to border on the head face 17a of the protrusions 14, 15.

In this embodiment the protrusions 14, 15 provided by the helically meandering profiled line of the cut pattern 12, 13 are following the pitch such that the axis A of the stem 16 is substantially perpendicular to the pitch. Thereby, the stem axis A forms an angle with the center axis of the tubular wall structure corresponding to the pitch angle to the center axis of the tubular wall structure.

In this embodiment of figure 3, the height 17d of the first head width section 17b and the height 17e of the second head width section 17c is equal to each other and the head face 17a is substantially parallel with the pitch.

The portion of the cut pattern shown in figure 4 comprises a slit sections 21 and cutout sections 22 providing a protrusion 24 comprising a stem 26 and a head 27 with a head surface 27a. The protrusion 24 is of the staggered type corresponding to the protrusions 4, 5 of the embodiment of figure 1. The stem has a first side 26a and a second side 26b, where the second side 26b is longer than the first side 26a. The height 27d of a first head width section 27b is larger than the height 27e of the second head width section 27c.

As illustrated the corners of the head 27 of the protrusions 24 are rounded, which ensures a desired high strength of the interlocked protrusions.

The portion of the cut pattern shown in figure 5 comprises a slit section 31 (also called a window) and cutout sections 32 providing interlocked protrusions 34, 35 comprising a stem 36 and a head 37 with a head surface 37a.

In the embodiment of figure 5, the head 37 is a T shaped head, wherein the head extends beyond the width of the stem at only one of the sides of the stem 36.

The windows 32 are located to border on the stems 36 of the protrusions 34, 35. The bend limiter is now in its first short stage. Upon displacement to the second displaced stage of the bend limiter, the windows will be located to border on the head face 37a.

The stem has a height 36a and the head has a height 37b.

In the first short stage of the bend limiter, the windows each have a height 32a and a width 32b.

The axis A of the stem 36 is perpendicular to the not shown pitch axis. Thereby, the stem axis A forms an angle to the center axis of the tubular wall structure, which corresponds to the pitch angle.

The portion of the cut pattern shown in figure 6 comprises a slit section 41 (also called a window) and cutout sections 42 providing interlocked protrusions 44, 45, where only one full protrusion 44 is shown in the figure 6. Each protrusion 44 comprises a stem 46 and a head 47 with a head surface 47a. The head surface 47a is convex, which ensures an increased robustness of the protrusion in operation, enabling the individual protrusion to withstand a surprisingly high load. The protrusion 44 shown in figure 6 is of the staggered type, where the protrusions 44, 45 have a protrusion direction and a stem axis A substantially parallel to the center axis of the tubular wall structure.

The portion of the cut pattern shown in figure 7 corresponds to the cut pattern portion of figure 4 with slightly different dimensions. As mentioned elsewhere herein, it has been found that due to the cutout sections, the slit sections may be very narrow, This means that the slit sections may be provided by single slit cuts, even when using narrow laser cuts, so that it is not required to cut in along previous cutting path, but only cutting once along a cutting path.

The cut pattern along the profiled line comprises slit section 21 and cutout sections 22 may for example be provided as illustrated in figure 7 and described in the following:

Cutting along the profiled forming a first slit section 21a from point I to reaching a corner point II of a selected location for a cutout section 22. The corner point II also constitute an end point II of the cut slit section 21a.

Cutting out the cutout section 22 comprising, from the corner point/slit end point II, cutting along a first periphery line cl forming the cutout section to a turning point III and cutting a cross cut back along a cross line c2 to the turning point III or immediately adjacent to corner point/slit end point II and cutting along a second opposite periphery line c3 forming the cutout section to or immediately adjacent to the turning point III.

Cutting a second slit section 21b by cutting from the turning point III to a next corner point IV of a selected location for a cutout section 22. The corner point IV also constitute an end point of the second slit section 21b.

Cutting out the cutout section 22 comprising, from the corner point/slit end point IV, cutting along a first periphery line cl' forming the cutout section to a turning point V and cutting a cross cut back along a cross line c2 to the 1 turning point III or immediately adjacent to corner point/slit end point V and cutting along a second opposite periphery line c3' forming the cutout section to or immediately adjacent to the turning point V.

Cutting a third slit section 21c from the turning point V and so on.

This method provides a very effective cutting, which does not require cutting along previous cut paths. As mentioned elsewhere herein, it may be advantageous to provide the cut pattern to comprise one or more weak links in the form of short non-through cut length sections along the profiled line, wherein the weak links are adapted to rupture when the bend limiter is in use. Thereby, the tubular wall structure can be held in very stable condition during the cutting process, i.e. the tubular wall structure may be held in its first short stage.

As illustrated in figure 7 a weak link 29 is located at the head face 27 of the protrusion 24. The weak link may be as described above. Preferably, the weak link 29 is very short, such as with a length along the cutting line of 5 mm or less, such as 3 mm or less, such as 2 mm or less, such as 1 mm or less or even 0.5 mm or less.

The flexible member installation shown in figure 8 is a subsea installation and it comprises a flexible member 59 and a first and second bend limiter 54, 55. Each of the bend limiters comprises a tubular wall structure comprising a cut pattern as described above.

The installation comprises a subsea structure comprising a monopile 58, with a through opening 58a. The subsea structure comprises an internal connection platform 52, above which a generator may be located, such as a generator associated to a wind turbine or a wave power farm. The monopile 56a is fixed at the seabed S, e.g. by being partly buried therein.

At the internal connection platform 52 a number of connectors 53 are located, through which flexible members may be passes into the generator. The flexible member 59, is passing through the opening 58a of the monopile 58. The first bend limiter 55 is located to house a length section of the flexible member 59 outside the monopile 58 and a second bend limiter 44 is located to house a length section of the flexible member 59 inside the monopile 48. a retainer 51 for retaining the flexible member 59 in position relative to the opening 58a is located between the first bend limiter 55 and the second bend limiter 54 thereby also retaining the the first bend limiter 55 and the second bend limiter 54 in position. The first bend limiter 55 and the second bend limiter 54 may advantageously be connected to the retainer 51. The retainer may advantageously be as the retaining portion described in copending application DK PA 2021 00156, however, it should be understood that any suitable retainer may be applied.

The flexible member 59 extends from a location outside of the monopile 58, where it is resting on the seabed S, through the first bend limiter 55, through the retainer 51, through the second bend limiter 54 and through the connector 53 at the internal connection platform 52, where it is held in a temporarily or stationary fixed position.

At least one of the first bend limiter 55 and the second bend limiter 54 is a bend limiter according to an embodiment of the invention.

A not shown sacrificial anode may advantageously be fixed to at least one of the first bend limiter 55 and the second bend limiter 54 and/or a sacrificial anode may be fixed to the retainer 51.

The first bend limiter 55, located outside the subsea structure is advantageously housing the flexible member from a location of up to 2 m from the retainer 51 to a location where it is resting on the seabed S. The first bend limiter 55, located outside the subsea structure advantageously has a length of at least 5 m, preferably at least 10 m.

The second bend limiter 54, located inside the subsea structure, need not be too long, e.g. a length of from 1 to 5 m may suffice. The flexible pipe installation shown in figure 9 is a subsea installation comprising a flexible member 69, a first bend limiter 65 and a second bend limiter 64. The installation further comprises a monopile 68 with a through opening 68a. The first bend limiter 65, the second bend limiter 64 and a retaining member 61 forms a protection arrangement protecting the flexible member. Thereby, the protection arrangement 64, 61, 65 comprises from its proximal end (inside the monopile 68) to its distal end (outside the monopile 68) the second bend limiter 64, the retainer 61, the first bend limiter 65. A portion of the flexible member 69 is housed in the protection arrangement 64, 61, 65.

The protection arrangement 64, 61, 65 has been installed through the opening 68a in the monopile 68. The top part of the monopile 68 is not shown but may for example provide a support for a generator, such as a generator associated to a wind turbine or a wave power farm. The monopile is fixed at the seabed S, e.g. by being partly buried therein.

The first bend limiter 65 is composed of a first bend limiter portion 65a and a second bend limiter portion 65b, wherein the first bend limiter portion 65a and the second bend limiter portion 65b are connected to each other at connection flanges 15c. The connection flanges 65c, may for example be connected using not shown screws and bolts.

The retainer 61 may be as in the embodiment of figure 8.

The protection arrangement 64, 61, 65 further comprises a number of sacrificial anodes 66a, 66b, which in principle may be located at any location.

The flexible member has been pulled through the protection arrangement 14, 11, 15.

At least one of the first bend limiter portion 65a and the second bend limiter portion 65b of the first bend limiter 15 and/or the second bend limiter 14 is a bend limiter according comprising a tubular wall structure with a cut pattern as describe above.

Figure 10 shows a flexible member installation comprising a flexible member in the form of a flexible riser pipe 79, a first bend limiter 74 and a second bend limiter 75.

The offshore system shown in Fig. 10 comprises a riser 1 of the invention arranged for transporting fluid between an upper facility 2 and a not shown subsea facility. The upper facility 2 is a floating unit e.g. a vessel or a platform. Such a floating unit will often be moored using tethering lines or similar. The upper facility 2 is floating at the water line 9.

The riser pipe is for example of the unbonded type APU7J, Fourth Edition, "Specification for Unbonded Flexible Pipe" or APU7B, Fifth Edition "Recommended Practice for Flexible Pipe".

The riser pipe is arranged for transporting fluid between an upper facility 72a and a subsea facility 76. The upper facility 72a is arranged below the water line W and may for example be a mid-water arch or another submerged facility. A vessel 72b is connected to the upper facility 72a via a jumper 78, which can for example be n flexible pipe of the unbonded type with metal armor(s) and/or composite armor(s).

In an upper section of the riser pipe 79 immediately adjacent to the fixation of the riser pipe 79 to the upper facility 72a, the riser pipe 79 is housed in the first bend limiter 74 for preventing excessive bends. The connection between the riser pipe 79 and the upper facility 72a may be relatively rigid, which makes the upper section of the riser pipe 79 sensitive to bends exceeding a certain minimum bending radius (MBR), where the MBR depends on the pipe structure and diameter. The first bend limiter is advantageously a bend limiter according to an embodiment of the bend limiter of the invention as described above. Besides the benefits described above, the bend limiter also is beneficial in that it does not prevent seawater to be in contact with and optionally cool down the upper section of the riser pipe 79.

A lower section of the riser pipe 79 is arranged to have a touch down point where it touches the seabed S and leads further to the subsea facility 76. Such touch down point may repeatedly be lifted from and laid back onto the seabed e.g. due to movements of the upper facility 72a. This may put the riser pipe in risk of overbending and mechanical damaging. To prevent this, the lower section of the riser pipe 79 is housed in and protected by the second bend limiter 75. Advantageously, the second bend limiter 75 is a bend limiter according to an embodiment of the bend limiter of the invention as described above.