GB2487506A

GB2487506A - Stiffener for a flexible pipe

Info

Publication number: GB2487506A
Application number: GB1207043.9A
Authority: GB
Inventors: Frederic Demanze; Alain Chalumeau
Original assignee: Technip France SAS
Current assignee: Technip Energies France SAS
Priority date: 2009-11-03
Filing date: 2010-11-04
Publication date: 2012-07-25
Anticipated expiration: 2030-11-04
Also published as: GB201207043D0; WO2011055090A1; DK180014B1; GB2487506B; DK201270238A; FR2952118B1; FR2952118A1; MY161125A; BR112012010421B1; NO20120489A1; NO346686B1; BR112012010421A2

Abstract

The invention relates to a stiffener (12) for a flexible pipe (10) manufactured from a polyurethane elastomer composition, which is obtained from a methylene diphenylene diisocyanate prepolymer composition (MDI prepolymer), which is then cross-linked with a polyamine in order to form the polyurethane elastomer composition suitable for being shaped such as to manufacture the stiffener.

Description

Stiffener for a flexible pipe The invention relates to a bend stiffener for a flexible pipe.

Bend stiffeners are placed around the pipe at locations where the flexible pipe will be subjected to high stresses induced by the movements of the boat or of the swell. A bend stiffener is constituted of a molded plastic structure of conical shape having a length of a few meters and that is intended to surround the pipe.

By reinforcing the flexible pipe with a bend stiffener at the most stressed point, the pipe is prevented from bending beyond its minimum radius of curvature, beyond which the pipe would suffer irreversible damage of its structure.

The flexible pipes that raise fluids (hydrocarbons, for example) from the wellhead are connected to the surface installation by passing through a steel guide tube that may be straight or bent, "I-tube" or "J-tube" respectively. Several guide tubes are provided on the surface installation. During the raising of the flexible pipe, this pipe is guided and drawn through a guide tube in order to connect the end of the pipe to the surface installation. In operation, the amplitude of the movements of the flexible pipe generated by the movements of the swell may lead to a deterioration of the structure of the flexible pipe in the vicinity of the guide tube for example. To prevent such damage to the flexible pipe, a bend stiffener surrounds the flexible pipe in the vicinity of the guide tube. The bend stiffener is then attached to the end of the guide tube by a clamp in a known manner.

The bend stiffener is generally located under the workstation of the surface installation, in a submerged or partly submerged medium. Furthermore, the bend stiffener is subjected to numerous elongation and compressive stresses generated by the movements of the surface installation and of the flexible pipe under the effect of sea currents, wind and/or swell. The conditions experienced by the bend stiffener could lead to premature aging of the plastic in the long term which could damage the integrity of the flexible pipe.

In order to limit these phenomena, the bend stiffeners are manufactured from plastic having good hydrolysis resistance and elongation resistance characteristics.

One material that brings together the best characteristics is polyurethane. Currently, a bend stiffener is manufactured, for example, from an Adiprene Ll67 TDI-polyether having a Shore A hardness of 95. For a service life of 20 to 30 years, the maximum hydrolysis resistance temperature of this material is 50°C.

The bend stiffeners conventionally manufactured may reach several meters in length, with thicknesses of greater than 200 -for a weight which may exceed 2 tonnes. To limit the size and weight of the bend stiffeners, polyurethanes are chosen with relatively high hardnesses, typically above 90 Shore A. In this hardness range, the difficulty of polyurethane processability increases with the hardness.

Specifically, the more the hardness of the polyurethane increases, the shorter the pot life of the mixture prepared from a prepolymer based on diisocyanate and on a chain extender such as polyamines or polyalcohols, which requires the use of high-throughput casting machines, especially when it is a question of molding large-sized parts.

One objective of the invention is to propose a bend stiffener that has an aging resistance improved by at least 10°C compared to the bend stiffener of the prior art, while ensuring a good homogeneity of the mechanical properties.

Another objective of the invention is to enable the manufacture of a bend stiffener that has a higher hardness compared to the bend stiffener of the prior art, of 60 Shore D for example, while ensuring a good homogeneity of the mechanical properties.

The third advantage is to enable the manufacture of a bend stiffener, the processability of which is improved

compared to the bend stiffener of the prior art.

Surprisingly, it has been found that a polyurethane elastomer prepared from a diphenylmethane diisocyanate (MDI) prepolymer and the chain extender chosen from polyamines could be used for the manufacture of a bend stiffener. The bend stiffener thus manufactured then has an even greater aging resistance compared to the known bend stiffener and also improved processability.

This improvement in the processability makes it possible to produce a bend stiffener having higher hardness.

According to one particular embodiment of the invention, the polyurethane elastomer is prepared from a diphenylmethane diisocyanate (MDI) prepolymer and from a methylenedianiline salt. This embodiment is particularly advantageous for carrying out a cold casting of the bend stiffener. The cold casting of the bend stiffener is particularly advantageous insofar as it does not reguire very complex equipment.

The description which follows will present, in detail, the embodiments of the invention and other advantages with reference to the appended drawing: -figure 1 is a transverse cross-sectional view of a flexible pipe equipped with a bend stiffener according to the invention.

Figure 1 schematically shows a flexible pipe (10) provided with a bend stiffener (12) . The flexible pipe is inserted through the guide tube (14) of the surface installation (not represented) . The bend stiffener is placed level with the pipe so that during the connection of the flexible pipe to the surface installation, the bend stiffener is level with the mouth of the guide tube, thus protecting the flexible pipe from any damage during movements of the boat. The bend stiffener is then attached by a clamp (not represented) or any other known means around the end of the guide tube.

According to the invention, the bend stiffener is manufactured from a novel polyurethane composition. The polyurethane used for manufacturing the bend stiffener is obtained from a diphenylmethane diisocyanate prepolymer (MDI prepolymer) composition. This prepolymer is then crosslinked with a polyamine in order to form the polyurethane elastomer composition capable of being formed in order to manufacture the bend stiffener.

The polyurethane elastomer is thus prepared according to a two-step process. In a first step, an intermediate prepolymer is prepared by condensation of the alcohol functions of a polyol with the isocyanate functions of a polyisocyanate. In a second step, the prepolymer and the crosslinking agent are preheated and mixed in a casting machine, then the mixture is injected into a preheated mold in the shape of the bend stiffener, and finally this mold is kept at temperature in an oven for the duration of the crosslinking.

This manufacturing process makes it possible to more easily control the characteristics of the final material, which has an advantage when it is a question of molding parts that require large amounts of material, as is the case with the bend stiffener.

According to a first step, an intermediate diphenyl-methane diisocyanate prepolymer (MDI prepolymer) is synthesized.

The MDI prepolymer is obtained by reacting, at a temperature between 30 and 150°C, an MDI diisocyanate with a polyol of high molecular weight between, for example, 250 and 10 000 g.moF'. The ratio between the number of N=CO functions and the number of OH functions in the reaction mixture may be between 1.5 and 20. The reaction temperature is, for example, between 30 and 150°C.

The MDI diisocyanate used for the preparation of the MDI prepolymer is selected from 2,4'-diphenylmethane diisocyanate and 4,4'-diphenylmethane diisocyanate or else 2, 2' -diphenylmethane diisocyanate.

Alternatively, from 0 to 20% by weight of an aliphatic diisocyanate may be added to the MDI prepolymer composition. The aliphatic diisocyanate is then chosen from the group consisting of 1,1'-methylenebis- (4-isocyanatocyciohexane), 1, 4-cyclohexane diisocyanate, isophorone diisocyanate (IPDI), 1, 3-xylene diisocyanate, hexamethylene diisocyanate and 1,1,4,4-tetramethylxylene diisocyanate or a mixture of one of these compounds.

Preferably, the high molecular weight polyol is chosen from the group of polyether glycols and polyester glycols.

In the remainder of the text, the expression "diphenyl-methane diisocyanate prepolymer composition" is defined as a composition containing at least 80% of diphenyl-methane diisocyanate prepolymer obtained by the reaction of at least one polyol and of a diisocyanate monomer and may also comprise an amount of free MDI monomer or other solvent or plasticizer.

According to a second step, the MDI prepclymer composition is then reacted with a crosslinking agent in a ratio of the order of the stoichiometry selected from polyamines and preferably aromatic polyamines. The ratio between the total number of N=CO functions in the MDI prepolymer composition and the number of NH2 functions in the reaction mixture is substantially of the order of the stoichiometry. For example, it may be between 0.7 and 1.2.

Preferably, the polyamines are chosen from aromatic polyamines. By way of example, the polyamine may be 4,4'-methylenebis(2-chloroaniline), 3,5-diamino-4- chlorobenzoic acid isobutyl ester or else 4,4'-inethylenebis (3-chloro-2, 6-diethylaniline) The mixture constituted of the prepolymer composition and of the crosslinking agent is injected into a preheated mold having the conical shape typical of a bend stiffener. This mold is maintained at temperature in an oven for the duration of the crosslinking and finally the bend stiffener is demolded.

Patent application HP 1 950 234 typically discloses a novel polyurethane elastomer that can be used for manufacturing a bend stiffener according to the first embodiment of the invention.

Specifically, HP 1 950 234 discloses a polyurethane elastomer obtained from a prepolymer comprising 2,4'-diphenylmethane diisocyanate prepared according to a process that comprises the following steps: (a) Reacting diphenylmethane diisocyanate (MDI) comprising more than 80% of 2,4'-diphenyl-methane diisocyanate with a high molecular weight polyol selected from the group of polyalkylene ether polyols having a molecular weight between 250 and 10 000 g.moF' at a temperature between 30 and 150°C for a sufficient time to form the 2,4'-MDI prepolymer and to react the OH functions of the polyol with a ratio between the NCO functions and the OH functions of between 1.5:1 and 20:1.

(b) Adding to the 2,4'-MDI prepolymer an aliphatic diisocyanate chosen from 1,1'-methylenebis(4-isocyanatocyclohexane), 1,4-cyclohexane diisocyanate, isophorone diisocyanate (IPDI), 1,3-xylene diisocyanate, hexamethylene diisocyanate and 1, 1, 4, 4-tetramethyixylene diisocyanate or a mixture of one of these compounds.

(c) Adding a necessary amount of aliphatic and/or aromatic diamine or polyamine whereby the constituents will react such that the ratio between the eguivalent of NCO groups and the sum of the free NCO groups is between 0.8:1 and 1.2:1.

The method of synthesis disclosed in EP 1 950 234 is a possible route for obtaining a polyurethane elastomer through the formation of a 2,4'-MDI prepolymer composition, crosslinked by an aliphatic or aromatic polyamine and hot cast in order to manufacture a bend stiffener.

Whereas previously the crosslinking of an MDI prepolymer with a polyamine was dismissed due to their excessively high reactivity with respect to MDIs, patent application EP 1 950 234 discloses a novel route for the synthesis of polyurethane elastomers by reaction of a composition containing an MDI prepolymer and a polyamine where the reaction parameters are controllable.

The bend stiffeners prepared from a polyurethane elastomer synthesized by reacting a composition comprising an MDI prepolymer and a polyamine have better hydrolysis resistance characteristics and a better fatigue strength than the bend stiffeners manufactured from polyurethane elastomers of the prior art, while retaining homogeneous mechanical properties in the regions of large thicknesses, typically 100 mm to 500 mm. Moreover it is possible, still retaining the homogeneity of the mechanical properties, to obtain bend stiffeners of greater hardness. Finally, one important advantage is the better processability of the polyurethane insofar as the formulations based on MDI prepolymer and a polyamine make it possible, during molding, to ensure a cohesion between the molded part that has already set and the rest of the formulation which has not yet been set.

The characteristics of the material thus obtained make it possible to achieve a hardness of between 50 Shore D and 70 Shore D while ensuring homogeneous properties within the material. The hardness measurements are carried out according to the standard ISO 868 or ASTM D2240. The material obtained also has a hydrolysis resistance up to 60°C for 30 years, or even 70°C for shorter durations, and a fatigue strength that is increased by a factor of 2 to 10 depending on the operating conditions. The hydrolysis resistance measurements are carried out by tensile tests according to the standard ASTM D638 on test specimens that have been subjected to accelerated aging in water, and by extrapolation according to Arrhenius law.

A seccnd particular embodiment of the invention will now be described. In this particular embodiment of the invention, the diisocyanate prepolymer is crosslinked with a particular family of amines, the reactive amine functions of which are blocked to reduce their reactivity with respect to the MDI prepolymer.

The polyurethane elastomer used for manufacturing the bend stiffener is obtained from a diphenylmethane diisocyanate prepolymer (MDI prepolymer) composition which is then crosslinked with a complex of methylene-dianiline (MDA) salts in order to form the polyurethane elastomer composition capable of being cold formed in order to manufacture the bend stiffener. The expression "cold forming" should be understood to mean that the filling of the mold can take place without needing to preheat the mold or even the reactants (except for ensuring the degassing) and that the crosslinking reaction does not take place during the filling of the mold. This enables a slow and controlled filling of the mold, thus avoiding the formation of bubbles, the crosslinking being carried out in a second step during the increase in temperature of the material introduced into the mold having the shape of the bend stiffener.

The methylenedianiline (MDA) salt is a poiyamine, the amine functions of which are blocked in order to reduce the reactivity of the amine with respect to the MDI prepolymer at the moment of the crosslinking of the MDI prepolymer composition and thus to be able advantageously to carry out cold casting of the bend stiffener. During the cold casting phase, the amine functions of the MDA salt will be unblocked by a controlled increase in temperature in order to react with the MDI prepolymer composition. The gradual unblocking of the amine functions of the MDA salt complex makes it possible to reduce the reactivity of the crosslinking agent and to advantageously carry out cold casting of the bend stiffener.

-10 -The polyurethane elastomer is prepared according to a three-step process. In a first step, an intermediate prepolymer composition is prepared by condensation of the alcohol functions of a polyol with the isocyanate functions of a polyisocyanate as described previously for the first embodiment of the invention.

In a second step, the MDI prepolymer and the MDA salt are mixed, preheated around 70°C, to ensure a degassing of the mixture.

The methylenedianiline (MDI) salt is advantageously the tris (4, 4'-diaminodiphenylmethane) -NaCl complex obtained between methylenedianiline (MDA) and the sodium chloride salt. Optionally, this salt may comprise a plasticizer. It is, for example, sold under the brands CAYTUR 31TN and CAYTUR 31_DATM.

The mixture is then injected into a mold having the shape of a bend stiffener.

In a third step, the mold, which will have been able to be preheated beforehand is introduced into an oven, the temperature increase of which is controlled. During this last step, the temperature increase profile of the oven is adjusted in order to gradually unblock the amine functions of the MDA salt and crosslink the MDI prepolymer.

In this particular embodiment, the reaction time leading to: the formation of the polyurethane elastomer is longer due to the controlled reactivity of the selected crosslinking agent. Thus, it is not necessary to use high-throughput casting machines. Furthermore, the bend stiffener manufactured from the polyurethane elastomer obtained from an MDI prepolymer crosslinked with the methylenedianiline (MDA) salL has mechanical -11 -characteristics comparable to those obtained with the bend stiffener obtained according to the first embodiment of the invention.

Patent application NO 2009/108510 typically discloses a novel polyurethane elastomer that can be used to manufacture a bend stiffener by the technique of cold casting according to the second embodiment of the invention. Therefore, the teaching of patent application NO 2009/108510 is incorporated by reference into the patent application.

NO 2009/108510 discloses a polyurethane elastomer composition obtained by reaction of an MDI prepolymer and of methylenedianiline complexed with a sodium chloride salt, the mixture of which is stable over time for several days at the degassing temperature of 70°C.

This mixture is then introduced into a mold having the shape of a bend stiffener and heated at a crosslinking temperature to be determined between 115 and 130°C in order to unblock the blocked amines of the MDA complex and initiate the crosslinking reaction of the MDI prepolymer composition.

The crossiinking reaction takes place under almost stoichiometric conditions. The stoichiometry is determined by the ratio between the total number of N=CO functions in the MDI prepolymer composition and the total number of NH2 functions unblocked at the crosslinking temperature of the MDI prepolymer. This ratio can be easily determined and may be between 0.7

and 1.2 for example.

The bend stiffener thus obtained has improved properties in a manner identical to that which is described for the first embodiment of the invention.

Claims

-12 -Claims: 1. A flexible pipe bend stiffener manufactured from polyurethane, said polyurethane is obtained by reacting, in a ratio between 0.7 and 1.2, a composition comprising at least 80% of a diphenyl-methane diisocyanate (MDI) prepolymer and a polyamine.
2. The bend stiffener as claimed in claim 1, characterized in that the diphenylmethane diisocyanate prepolymer composition also contains up to 20% by weight of an aliphatic diisocyanate chosen from 1, 1'-methylenebis (4-isocyanatocyclo-hexane), 1,4-cyclohexane diisocyanate, isophorone diisocyanate (IPDI), 1,3-xylene diisocyanate, hexamethylene diisocyanate and 1,1,4, 4-tetra-methylxylene diisocyanate or a mixture of one of these compounds.
3. The bend stiffener as claimed in either of the preceding claims, characterized in that the polyamine is chosen from 4,4'-methylenebis- (2-chloroaniline), 3,5-diamino-4-chlorobenzoic acid isobutyl ester and 4,4'-methylenebis- (3-chloro-2, 6-diethylaniline)
4. The bend stiffener as claimed in claim 1 or 2, charabterized in that the polyamine is the tris (4,4' -diaminodiphenylmethane) -NaC1 complex and in that the bend stiffener is cold cast.
5. The bend stiffener as claimed in one of the preceding claims, characterized in that the diphenylmethane diisocyanate prepolymer is synthesized by reacting a diphenylmethane diisocyanate and a polyol having a molecular weight between 250 and 10 000 g.molT' chosen from -13 -the group of polyester glycol and polyether glycol and in that the ratio between the number of N=0O functions and the number of OH functions in the reaction mixture is between 1.5 and 20.
6. The bend stiffener as claimed in claim 5, characterized in that the polyol is chosen from the polyether glycol family.
7. The bend stiffener as claimed in claim 1, characterized in that the diphenylmethane diisocyanate is 2,4'-diphenylmethane diisocyanate.
8. The bend stiffener as claimed in claim 3, characterized in that it is hot cast.
9. The bend stiffener as claimed in one of the preceding claims, characterized in that the hardness of the bend stiffener is greater than or equal to 50 Shore D with a hydrolysis resistance of at least 50°C over a period of 20 years.