DK202200051A1

DK202200051A1 - Method of curing a curable resin

Info

Publication number: DK202200051A1
Application number: DKPA202200051A
Authority: DK
Inventors: Wang Christian
Original assignee: Wang Christian
Priority date: 2022-01-19
Filing date: 2022-01-19
Publication date: 2022-02-18

Abstract

A method of curing a curable resin, comprising supplying the curable resin at at least one selected location in an end-fitting, providing at least one dielectric sensor in the curable resin and providing the resin to cure in a curing process, wherein the at least one dielectric sensor forms part of a dielectric analysis system (DEA), preferably the at least one dielectric sensor is a disposable sensor.

Description

DK 2022 00051 A1 1

METHOD OF CURING A CURABLE RESIN

TECHNICAL FIELD The present invention relates to a method of curing a curable resin. Specifically, the invention relates to a method of curing a curable resin supplied to or located in an end-fitting such as in connection with the mounting of the end-fitting to an unbonded flexible pipe.

BACKGROUND ART Unbonded flexible pipes as well as end-fitting therefor and assemblies thereof are well known in the art and are for example described in the standard "Recommended Practice for Flexible Pipe”, ANSI/API 17 B, fifth Edition, 2014, and in the standard “Specification for Unbonded Flexible Pipe”, ANSI/API 17], Fourth edition, 2014.

An unbonded flexible pipe comprises a plurality of layers and is preferably suitable for offshore, onshore and/or subsea transportation of fluids like hydrocarbons, CO2, water and mixtures hereof. In particular, the flexible pipe may be a riser pipe of the unbonded type.

Such pipes usually comprise an inner liner also often called an inner sealing sheath or an inner sheath, which is the innermost sealing sheath and which forms a barrier against the outflow of the fluid, which is conveyed in the bore of the pipe, and one or more armouring layers. Often the pipe further comprises an outer protection layer, which provides mechanical protection of the armour layers. The outer protection layer may be a sealing layer sealing against ingress of seawater. In certain unbonded flexible pipes, one or more intermediate sealing layers are arranged between armour layers.

In this text the term "unbonded” means that at least two of the layers including the armouring layers and polymer layers are not bonded to each other. In practice, the known pipe normally comprises at least two armouring layers located outside the inner sealing sheath and optionally an armour

DK 2022 00051 A1 2 structure located inside the inner sealing sheath normally referred to as a carcass.

The armouring layers usually comprise or consist of one or more helically wound elongated armouring wires, where the individual armour layers are not bonded to each other directly or indirectly via other layers along the pipe.

Thereby the pipe becomes bendable and sufficiently flexible to roll up for transportation.

The end-fitting is usually coupled to the unbonded flexible pipe to terminate at least an armour layer, such as a tensile armour layer.

In most situations, the end-fitting is coupled to the unbonded flexible pipe to terminate all of the layers of the unbonded flexible pipe.

The end-fitting is normally relatively stiff since the coupling between the unbonded flexible pipe and the end-fitting must be strong.

To ensure a strong and durable connection between the one more armour layers and the end-fitting, it is well known to use a curable resin in the end- fitting, which curable resin is subjected to a curing process.

After the end-fitting has been fully assembled when applied to terminate the unbonded flexible pipe, it is not possible to take out samples of the cured resin for testing e.g. the mechanical strength and/or the fixation strength without destroying the assembly of the end-fitting and the unbonded flexible pipe.

In prior art assemblies of end-fitting and unbonded flexible pipe it has often been found that the fixation between the end-fitting and the unbonded flexible pipe has been insufficient.

In most cases, this defect is found during the Factory Acceptance Test (FAT). In such situation, the end-fitting must be removed and a new end-fitting must be mounted to the unbonded flexible pipe.

This in both very expensive, time demanding and may delay the entire production.

However, in the worst case such a defect may not be found under FAT, and this may result in a catastrophical failure of the flexible pipe /end-

DK 2022 00051 A1 3 fitting assembly during use, which beyond being extraordinary costly, may also be very dangerous to people and other equipment at the location of the use.

DISCLOSURE OF INVENTION The object of the invention is to provide a method of ensuring sufficient mechanical strength of the cured resin. In an embodiment, it is an object to provide a method by which the risk of failure of the fixation between the end-fitting and the unbonded flexible pipe is reduced.

In an embodiment, it is an object to provide a method by which documentation for curing property or properties of a cured resin in an end- fitting can be provided.

In an embodiment, it is an object to reduce manufacturing time.

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

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. Reference made to “some embodiments” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with such embodiment(s) is included in at least one embodiment of the subject matter disclosed. Thus, the appearance of the phrases “in some embodiments” or “in an embodiment” in various places throughout the specification is not necessarily referring to the same embodiment(s). Further,

DK 2022 00051 A1 4 the skilled person will understand that particular features, structures, or characteristics may be combined in any suitable manner within the scope of the invention as defined by the claims. The term “substantially” should herein be taken to mean that ordinary product variances and tolerances are comprised. Throughout the description or claims, the singular encompasses the plural unless otherwise specified or required by the context. 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.

The phrase “winding angle” means a winding angle relative to the longitudinal center axis of the pipe (or merely called axis) when the pipe is in straight and unloaded condition.

The phrases “long pitch” and "short pitch” are relative terms i.e. the short pitch is shorter than the long pitch. A winding with an angle of about 75 degrees or larger relative to the pipe axis is generally considered to be a short pitch and a winding with an angle of about 55 degrees or shorter is generally considered to be a long pitch.

The term “cross-wound layers” means that the layers comprise wound elongate elements that are wound in opposite direction relative to the longitudinal axis of the pipe where the angle to the longitudinal axis can be equal or different from each other.

The resin, such as an epoxy material in the end-fitting may serve multiple purposes. One function is that the epoxy material is used for fixation of, for example, the tensile armour of the unbonded flexible pipe, and it should then be able to stand a high mechanical load from the weight of the flexible pipe in service or at a high pressurization as seen under FAT or in offshore service.

DK 2022 00051 A1 The inventor of the present invention has found that, the mechanical properties of the cured resin e.g. the epoxy material are highly dependent of its level of curing. In addition, a number of defects such as uneven curing, presence of undesired air bubbles or other inhomogeneities in the cured resin 5 may influence the mechanical properties.

The method of curing a curable resin comprises e supplying the curable resin at at least one selected location in an end- fitting, e providing at least one dielectric sensor in the curable resin and e providing the resin to cure in a curing process, wherein the at least one dielectric sensor forms part of a dielectric analysis system (DEA), preferably the at least one dielectric sensor is a disposable sensor.

The step of providing the at least one dielectric sensor in the curable resin may comprise arranging the at least one dielectric sensor at a selected sensor location prior to supplying the curable resin.

In a flexible pipe/end-fitting assembly, end-fittings are used for termination of the pipe structure, where one or more armour layers and other structural layers in the flexible pipe end and are fastened. The resin may advantageously be applied to anchoring wires of a tensile armour, such as a armour wound with long pitch. The tensile armour may during deployment and/or during use carry the weight of a long length of the pipe, even the entire length of the pipe. This high load is transferred to the end-fitting fully or partly via the anchoring formed at least partly by the cured resin.

As mentioned, the mechanical strength of the cured resin e.g. epoxy depends, as mentioned, on the crosslinking and to what degree of crosslinking has been achieved. Since the epoxy in the end-fitting is enclosed by metallic structural items, it is not possible to take samples for mechanical measurements to guarantee the quality of the epoxy. In an embodiment, the

DK 2022 00051 A1 6 idea for improving flexible pipes and their end-fittings is to introduce an in- situ measurement and monitoring of the epoxy curing process with Dielectic Analysis (DEA) by placing disposable DEA sensors (or DEA sensors) at selected sensor locations in the end-fittings before pouring the curable resin at the one or more selected location. Suitable DNA sensors and DEA analysis systems may for example be as marketed by the company Synthesites (e.g. SYNTHESITES UK LTD) or NETZSCH-Geratebau GMBH. In an embodiment, the method comprises anchoring at least one armour wire such as a plurality of armour wires of an unbonded flexible pipe in the end- fitting, wherein the at least one selected location of the supplied curable resin comprises a location of anchoring said at least one armour wire, wherein the method comprising embedding end portions of the respective armour wire(s) in the curable resin.

In practice, it may be desirable that a plurality of armour wires, such as all of the armour wires of a tensile armour layer is anchored by being embedded in the curable resin together with one or more DEA sensors and of an unbonded flexible pipe in the end-fitting.

In an embodiment, the method comprises anchoring at least one layer of an unbonded flexible pipe in the end-fitting, wherein the at least one selected location of the supplied curable resin comprises a location of anchoring said at least one layer, wherein the method comprising embedding an end portion of the at least one layer in the curable resin.

In an embodiment, the disposable DEA sensors can also be placed in locations other than for anchoring of armour wires and/or other pipe layers. This may include locations where the resin, such as epoxy performs another function, for example in inner casing where the epoxy supports certain structures.

DK 2022 00051 A1 7 In an embodiment, the at least one selected location of the supplied curable resin comprises a sealing location, such as a location adjacent to a polymer layer of the unbonded flexible pipe.

Often the curing process of the resin will generate heat.

For example using two component epoxy resin (a component comprising one or more polyepoxides and an epoxy hardener). In an embodiment, the end-fitting uses epoxy material consisting of a resin and a hardener component that is mixed together outside the end-fitting before it is poured as a liquid into the end-fitting at the desired location(s) at — which location one or more dielectric sensors have been placed, such that at least a portion of the sensor(s) is/are embedded in the resin/hardener mixture. . By mixing the epoxy hardener and the epoxy resin, the curing process starts, which is an exothermic chemical process.

The temperature rises during the curing process, as the resin and the hardener form chemical crosslinks.

This causes the epoxy to harden and solidify, and it becomes hard as a solid with an associated mechanical strength.

As mentioned, the mechanical strength of the epoxy depends on the crosslinking and to what degree of crosslinking reaches.

The time of the curing process as well as the temperature may influence the resulting mechanical properties of the cured epoxy.

The curing time depends on the temperature i.e. the higher temperature, the faster the curing process.

Thus, it may be desired to provide a high temperature to speed up the curing process.

However, a too high temperature may result in undesired defects.

A too high temperature may fully or partly degrade polymer parts located in the end-fitting, such as portions of polymer layers or sealings.

Even where the mixing of the two components is very thorough, there may be minor pockets with insufficient amount or to high amount of hardener, which may result in local defects depending of the temperature.

Thus, a too high temperature may result in generation of such uncured or low-cured pockets in the otherwise cured resin.

DK 2022 00051 A1 8 Advantageously, the method comprises monitoring temperature of the resin during at least a part of the curing process.

In an embodiment, the method comprises adjusting the temperature of the resin during at least a part of the curing process according to a selected temperature scheme.

The temperature adjustment may conveniently comprise supplying heat to the resin during at least a part of the curing process.

In an embodiment, the temperature adjustment comprises cooling the end-fitting, preferably at location of the end-fitting comprising polymer material.

In an embodiment, the cooling may be performed by applying a cooling medium in the bore of the end-fitting, preferably close to or in contact with a pressure layer of the unbonded flexible pipe.

The dielectric sensor may comprise a pair of electrodes optionally applied on and/or embedded in an inert material, such as a thin strip and/or film of inert material.

The dielectric sensor may preferably be very thin, e.g. less than 2 mm, such as less than 1 mm, such as less than, 0.5 mm or even thinner.

Wires from the DEA sensors may be routed out to the end-fitting for measuring equipment, and the sensors may be arranged as described above.

In an embodiment, the DEA measures the ionic viscosity (conductivity of the ions in the epoxy), and DEA measurements may provide information on when the crosslinking process is optimal and/or completed.

The DEA sensors may be applied for measuring ion viscosity, flow behaviour, reactivity, hardening monitoring, degree of crosslinking and/or glass transition temperature as well as for process monitoring and optimization.

The DEA sensors may be applied for providing a temperature monitor that can be used to control any heating and curing of the resin.

In an embodiment, the method of any one of the preceding claims, wherein the method comprises determining the Gel point and/or Tg value at one or more points of the curing process.

DK 2022 00051 A1 9 Advantageously, the method comprises determining possibly curing defects, such as curing defects caused by inhomogeneities in the resin, such as air bubbles, local uncured resin and inhomogene filler distribution. As mentioned the resin may conveniently be an epoxy resin (polyepoxides), such as a two-component epoxy resin. However, other curable resins may also be applied in the invention e.g. a polyester resin. The resin may optionally comprise a filler material, such as fibers.

In an embodiment, disposal/or non-disposal DEA-sensors are placed in the end-fitting as described above, and by using these sensors the curing process may be monitored to increase security for a desired curing of the resin and to provide documentation that the mechanical properties of the cured resin is within required specifications. Thereby, the risk of failure of the end- fitting/unbonded flexible pipe assembly is highly reduced. The solution of the present invention and embodiments thereof may in addition be fully compatible with existing QC test and further result in improving quality and documentation of product, which can be shown to a customer of the final product. In addition, it may be possible to reduce manufacturing time. Improved insight in curing process for failure analysis will potentially reduce rework processes. Multiple disposal/or non-disposal DEA-sensors can be placed in the end-fitting and/or heat can be applied to the end-fitting by heat control in connection with the sensors. The disposal/or non-disposal DEA-sensors can be used in every end-fitting — epoxy casting in production or used in the development of the epoxy curing process.

DK 2022 00051 A1 10 The invention also comprises a method of generating a temperature scheme for curing curable resin to obtain a cured resin with a desired mechanical strength, the method comprises providing two or more samples of the curable resin, providing at least one dielectric sensor in each of the curable resin samples and providing the resin to cure in a curing process, wherein the at least one dielectric sensor forms part of a dielectric analysis system (DEA), and wherein each of the samples is subjected to a temperature adjustment during at least a part of the curing process according to respective test temperature schemes, determining the mechanical strength of the respective cured resin samples, selecting the test temperature scheme for a cured resin having the desired mechanical strength as the generated temperature scheme.

The generated temperature scheme may be applied in the curing method as described above. The invention also comprises a method of generating a temperature adjustment scheme for curing curable resin to obtain a cured resin with a desired mechanical strength, the method comprises providing two or more samples of the curable resin, providing at least one dielectric sensor in each of the curable resin samples and providing the resin to cure in a curing process, wherein the at least one dielectric sensor forms part of a dielectric analysis system (DEA), and wherein each of the samples is subjected to respective test temperature adjustment schemes during at least a part of the curing process according to respective temperature schemes determined by the dielectric sensor(s), determining the mechanical strength of the respective cured resin samples, selecting the test temperature adjustment scheme for a cured resin having the desired mechanical strength as the generated temperature adjustment scheme.

DK 2022 00051 A1 11 The generated temperature adjustment scheme may be applied for curing of a curable resin in an end-fitting with or without dielectric sensors.

BRIEF DESCRIPTION OF THE EXAMPLES AND DRAWING The invention is illustrated further below in connection with embodiments and with reference to the figures. The figures are schematic and may not be drawn to scale.

Fig. 1 shows, partly in axial section, a typical flexible pressure pipe, Fig. 2 shows, in axial "section, an assembly of the flexible pressure pipe shown in fig. 1 and an end-fitting.

Fig. 3 is identical to fig 2 but with marking of desired locations for providing a dielectric sensor and supplying a curable resin to at least partly embed the sensor.

Fig. 1 shows a flexible pressure pipe, which is generally designated by 1. The pipe is of an unbonded structure comprising a number of layers, which in this embodiment are: — a carcass 2 of an interlocking structure made from metallic strips. The carcass serves, in the main, to prevent collapse of the pipe due to: pipe decompression, external pressure, tensile armour pressure and mechanical crushing loads, — an inner lining 3 also referred to as a pressure sheath, in the form of an extruded polymer layer for providing internal fluid integrity, - a pressure armour 4 in the form of structural layers consisting of helically wound C—shaped metallic strips or wires with a short pitch lay angle, — a tensile armour 5 consisting of a pair of helically cross wound armour layers each comprising a plurality of flat metallic tensile wires 6 with a lay

DK 2022 00051 A1 12 angle typically between 35 and 55 degreed to the pipe axis. The tensile armour serves to improve resistance to axial tensile loads, and - an outer sheath 7 in the form of an extruded polymer for shielding the structural elements of the pipe from the outer environment and providing mechanical protection. Fig. 2 shows an assembly 8 of an end-fitting 9 and the flexible pressure pipe

1. The end-fitting 9 forms the transition between the pipe and a connector and for this purpose has a first part 10 with a connection flange 11, a second part 12, and a third part 30. The three parts 10; 12; 30 delimit a cavity 13 — which partly is substantially cone-shaped. The end-fitting 9 has furthermore a through opening (Bore) 14 for accommodating an end of the pipe 1. -When assembling the flexible pressure pipe 1 with the end-fitting 9 the flat metallic wires 6 of the tensile armour 5 are led into the cavity 13 in the end- fitting, and a curable resin, preferably an epoxy resin, is injected into the cavity making an anchoring for the wires. Prior to the injection of the curable resin, dielectric sensor(s) may be applied in the cavity 13 to provide that the sensors will be at least partially embedded in the curable resin. The carcass 2 is fastened to the end-fitting 9 by means of a lock nut 15, and to the inner lining 3 by means of a lock ring 16 fitting into an annular groove 17 in the wall of the through opening 14. The lock ring 16 is in the embodiment shown secured in the groove 17 by a casting material 18, e.g. epoxy, which is injected through a hole 19. A ring 20 provides a stop for the lock nut 15. In the embodiment shown a sealing ring 21 for tightening the end-fitting 9 and the inner lining 3 is fitted into a groove 22 in the ring 20. After having removed the layers 4, 5, 7 surrounding the lining at the end of the pipe, two annular grooves 23 are rolled in the outer surface of the end part of the inner lining, whereafter the lock ring 16, which consists of one or more sectors of circle, is placed around said end part and secured with a

DK 2022 00051 A1 13 clamp 24. Not shown dielectric sensors and curable resin may be located adjacent to the annular grooves 23. In Fig. 3 the crosses indicate desired locations for providing a dielectric sensor and supplying a curable resin to at least partly embed the sensor.

Claims

DK 2022 00051 A1 1 PATENT CLAIMS

1. A method of curing a curable resin, the method comprising supplying the curable resin at at least one selected location in an end-fitting, providing at least one dielectric sensor in the curable resin and providing the resin to cure in a curing process, wherein the at least one dielectric sensor forms part of a dielectric analysis system (DEA), preferably the at least one dielectric sensor is a disposable sensor.

2. The method of claim 1, wherein the method comprises anchoring at least one armor wire such as a plurality of armor wires of an unbonded flexible pipe in the end-fitting, wherein the at least one selected location of the supplied curable resin comprises a location of anchoring said at least one armor wire, wherein the method comprising embedding end portions of the respective armor wire(s) in the curable resin.

3. The method of claim 1, or claim 2, wherein the method comprises anchoring at least one layer of an unbonded flexible pipe in the end-fitting, wherein the at least one selected location of the supplied curable resin comprises a location of anchoring said at least one layer, wherein the method comprising embedding an end portion of the at least one layer in the curable resin.

4. The method of any one of the preceding claims, wherein the at least one selected location of the supplied curable resin comprises a sealing location, such as a location adjacent to a polymer layer of the unbonded flexible pipe.

5. The method of any one of the preceding claims, wherein the method comprises monitoring temperature of the resin during at least a part of the curing process.

6. The method of any one of the preceding claims, wherein the method comprises adjusting the temperature of the resin during at least a part of the curing process according to a selected temperature scheme.

DK 2022 00051 A1 2

7. The method of claim 6 wherein the temperature adjustment comprises supplying heat to the resin during at least a part of the curing process.

8. The method of claim 6 or claim 7 wherein the temperature adjustment comprises cooling the end-fitting, preferably by applying a cooling medium in a bore of the end-fitting, preferably in contact with a pressure layer of the unbonded flexible pipe.

9. The method of any one of the preceding claims, wherein the dielectric sensor comprises a pair of electrodes optionally applied on and/or embedded in an inert material, such as a thin strip and/or film of inert material.

10. The method of any one of the preceding claims, wherein the method comprises determining the Gel point and/or Tg value at one or more points of the curing process.

11. The method of any one of the preceding claims, wherein the method comprises determining possibly curing defects, such as curing defects caused by inhomogeneities in the resin, such as air bobbles, local uncured resin and inhomogeneous filler distribution.

12. The method of any one of the preceding claims, wherein the resin in an epoxy resin, such as a two-component epoxy resin, wherein the epoxy resin optionally comprises filler material.

13. A method of generating a temperature scheme for curing curable resin to obtain a cured resin with a desired mechanical strength, the method comprises providing two or more samples of the curable resin, providing at least one dielectric sensor in each of the curable resin samples and providing the resin to cure in a curing process, wherein the at least one dielectric sensor forms part of a dielectric analysis system (DEA), and wherein each of the samples is subjected to a temperature adjustment during at least a part of the curing process according to respective test temperature schemes, determining the mechanical strength of the respective cured resin samples,

DK 2022 00051 A1 3 selecting the test temperature scheme for a cured resin having the desired mechanical strength as the generated temperature scheme.

14. A method of generating a temperature adjustment scheme for curing curable resin to obtain a cured resin with a desired mechanical strength, the method comprises providing two or more samples of the curable resin, providing at least one dielectric sensor in each of the curable resin samples and providing the resin to cure in a curing process, wherein the at least one dielectric sensor forms part of a dielectric analysis system (DEA), and wherein each of the samples is subjected to respective test temperature adjustment schemes during at least a part of the curing process according to respective temperature schemes determined by the dielectric sensor(s), determining the mechanical strength of the respective cured resin samples, selecting the test temperature adjustment scheme for a cured resin having the desired mechanical strength as the generated temperature adjustment scheme.