Chemical and gas-resistant, high-pressure, large-bore bonded flexible rubber pipe and method for producing the same

Abstract

A high-pressure, large-bore bonded flexible rubber pipe resistant to aggressive chemicals and gases, particularly for conveying gas or oil, the flexible pipe having a liner made of poly(vinylidene-fluoride) homopolymer or copolymer wherein a hydrogenated nitrile rubber-based, peroxide-vulcanized rubber compound 2 is bonded to the poly(vinylidene-fluoride) liner, which has a Mooney 05, 150 C. scorch time of at least 10 minutes. Further, a method for manufacturing such hoses, the method including vulcanization performed at a temperature of at least 160 C.

Claims

1. A high-pressure, large-bore bonded flexible rubber pipe resistant to aggressive chemicals and gases, the flexible pipe comprising a liner made of poly(vinylidene-fluoride) homopolymer or copolymer, with at least 80 mole % of the monomeric units being vinylidene-fluoride for the copolymer and a hydrogenated nitrile rubber-based rubber compound vulcanized with peroxide, the compound having a Mooney 05, 150 C. scorch time of at least 10 minutes, and the compound directly bonded to the poly(vinylidene-fluoride) liner.

2. The flexible rubber pipe according to claim 1, wherein the melting point of the PVDF liner is above 150 C.

3. The flexible rubber pipe according to claim 1, wherein the hydrogenated nitrile rubber-based rubber compound is vulcanized with a peroxide having a half-life at 150 C. of at least 1 hour.

4. The flexible rubber pipe according to claim 3, wherein the hydrogenated nitrile rubber-based rubber compound is vulcanized with either one of 2,5-dimethyl-2,5-di(t-butylperoxy)-3-hexyne,3,3,5,7,7-pentamethyl-1,2,4-trioxepane, di-tert-butyl peroxide, or a combination thereof.

5. The flexible rubber pipe according to claim 1, wherein the peroxide applied for vulcanizing the hydrogenated nitrile rubber-based rubber compound is a so-called scorch-protected peroxide.

6. The flexible rubber pipe according to claim 5, wherein the hydrogenated nitrile rubber-based rubber compound is vulcanized with peroxide scorch-protected di(tert-butylperoxy isopropyl)benzene.

7. A method for manufacturing the flexible pipe according to claim 1, comprising vulcanizing at a temperature of at least 160 C.

8. The method according to claim 7 wherein the vulcanization temperature is selected such that it differs from the melting range of the poly(vinylidene-fluoride) liner by at most +/10 C.

9. The method according to claim 8 wherein the vulcanization temperature is selected such that it differs from the melting range of the poly(vinylidene-fluoride) liner by at most +/5 C.

Description

(1) For better comprehension, the invention will be described below with reference to the accompanying drawings, without, however, restricting the invention to the embodiments depicted.

(2) FIG. 1 shows a schematic view of a possible embodiment of the 2-ply flexible pipe according to the invention.

(3) FIG. 2 shows a schematic view of a possible embodiment of the 3-ply flexible pipe according to the invention.

(4) FIG. 3 shows a schematic view of a possible embodiment of the 4-ply flexible pipe according to the invention.

(5) FIG. 4 shows a schematic view of a possible embodiment of the 6-ply flexible pipe according to the invention.

(6) FIG. 1 therefore shows a conceivable embodiment of the smooth-bore flexible pipe (not including an internal stripwound tube) according to the invention that comprises two reinforcing plies. A layer of HNBR rubber compound 2 cross-linked with peroxide encompasses the PVDF liner 1. Going radially outwards from the longitudinal axis of the flexible pipe, there are situated four rubberized textile layers 3, with the two reinforcing plies 4 (made of steel strands) being encompassed by a wire embedding rubber layer 5. The reinforcing plies 4 made of steel strands are covered by two rubberized textile layers 3 and by a rubber cover 6.

(7) FIG. 2 depicts another conceivable embodiment of the flexible pipe according to the invention. The flexible pipe 7 is encompassed by a PVDF liner 1. Going radially outwards from the longitudinal axis of the hose, there is situated a layer of peroxide cross-linked HNBR-based rubber compound 2 joined to the PVDF liner 1, with two rubberized textile layers 3 being situated above them, and three steel strands reinforcing plies 4 being encompassed by a wire embedding rubber layer 5. The reinforcing plies 4 made of steel strands are covered by a rubber cover 6.

(8) FIG. 3 illustrates yet another conceivable embodiment of the flexible pipe according to the invention. The flexible pipe 7 is encompassed by a PVDF liner 1. Going radially outwards from the longitudinal axis of the hose, there is situated a layer of peroxide cross-linked HNBR-based rubber compound 2 joined to the liner 1, with two rubberized textile layers 3 being situated above them, and four steel strands reinforcing plies 4 being encompassed by a wire embedding rubber layer 5. The reinforcing plies 4 made of steel strands are covered by two rubberized textile layers and by a rubber cover 6.

(9) In FIG. 4 another conceivable embodiment of the smooth-bore flexible pipe (not including an internal stripwound tube) according to the invention is illustrated, comprising six reinforcing plies. A layer of HNBR rubber compound 2 cross-linked with peroxide encompasses the PVDF liner 1. Radially outwards from the axis of the flexible pipe there is situated a wire embedding rubber layer 5. Six layers of reinforcing plies 4 (made of steel strands) are encompassed by a wire embedding rubber layer 5. The reinforcing plies 4 made of steel strands are covered by a rubber cover 6.

(10) The production method for manufacturing the flexible pipe according to the invention is illustrated by the following non-limiting example.

EXAMPLE 1

Manufacturing a Flexible Pipe with an Internal Diameter of 4 (102 mm) and an Operating Pressure of 69 MPa

(11) An interlocking-profile internal flexible stripwound tube 7, made of stainless steel, is situated inside the flexible pipe, which is encompassed by a PVDF liner 1 having a thickness of 6 mm. The liner 1 is made of PVDF copolymer thatin addition to vinylidene-fluoride (VF.sub.2)also contains a low amount of chlorotrifluoroethylene (CTFE). According to the manufacturer's data, its melting point is in the range of 170-174 C. A 1-mm-thick HNBR- (hydrogenated nitrile butadiene rubber) based rubber compound layer 2, with a Mooney 05, 150 C. scorch time of 12.0 minutes (according to the standard ISO 289) is bonded to the PVDF liner 1. For cross-linking, the HNBR-based rubber compound 2 was prepared with 8 phr (8 parts for 100 parts of elastomer by mass) of Trigonox 145 peroxide manufactured by Akzo-Nobel, the active agent being 2,5-dimethyl-2,5-di(t-butylperoxy)-3-hexyne, the active agent content and the half-life (ti/2) at 154 C. being 45% and 1 hour, respectively. The acrylonitrile content of the applied HNBR material is between 30% and 40%, with the residual double bond content being below 2%. The HNBR-based rubber compound 2 contained 70 phr of rubber-grade carbon blacks, 2.5 phr of triallyl isocyanate coagent, as well as a total of 18.7 phr of other additives (plasticizers, metal oxides, anti-aging agents, processing aids). The manufacturing of the flexible pipe was then continued in a conventional manner, by laying rubberized textile layers 3, a wire embedding rubber layer 5, and four steel strands reinforcing plies 4. Then, additional rubberized textile layers 3 and a rubber cover 6 were laid on the steel strands reinforcing plies 4. Finally, the flexible pipe was vulcanized at 175 C.

(12) Upon dissecting the flexible pipe, adhesion between the PVDF liner 1 and the HNBR-based rubber layer 2 was examined. What was found was so-called cohesive failure, implying that the PVDF remained covered with rubber over the entire surface, the adhesion value being above 10 N/mm measured according to the ISO 36 standard.

EXAMPLE 2 (COMPARATIVE EXAMPLE)

(13) As with the previous example, a flexible pipe with an internal diameter of 4 (102 mm) was manufactured in a manner similar to the above example, applying the same materials, with the sole difference that the Mooney 05, 150 C. scorch time of the HNBR-based rubber compound 2 was 5.6 minutes according to the ISO 289 standard. The peroxide applied for cross-linking (also in 8 mass fractions for 100 mass fractions of elastomer) was Perkadox 1440 made by Akzo-Nobel that did not contain scorch-protection agent. The active substance of Perkadox 1440 was di(tert-butylperoxy isopropyl)benzene, the concentration of the active substance was 40%, with the half-life (ti.sub./2) at 140 C. being 1 hour (i.e. at 150 C. significantly less than 1 hour). This flexible pipe was vulcanized at a temperature of 155 C. Upon dissecting the flexible pipe, adhesion between the PVDF copolymer liner and the HNBR-based rubber layer was examined. A so-called adhesive failure was found; the rubber layer has come apart from the PVDF over the entire surface, with the adhesion value being as low as 3.1 N/mm measured according to the ISO 36 standard, less than one-third of the value measured with the solution according to the invention.

EXAMPLE 3

Manufacturing a Flexible Pipe with an Internal Diameter of 3 (76 mm) and an Operating Pressure of 103.5 MPa

(14) The pipe is a so-called smooth-bore one, with the PVDF liner being its innermost layer. The liner was made of PVDF copolymer containing hexafluoropropene in addition to vinylidene-fluoride (VF.sub.2) and a low amount of plasticizer and having a melting point in the range of 166-170 C. A 1-mm-thick HNBR- (hydrogenated nitrile butadiene rubber) based rubber compound layer 2, with a Mooney 05, 150 C. scorch time of 14.0 minutes (according to the standard ISO 289) is bonded to the PVDF liner 1. For cross-linking, 7 phr of Luperox F40P-SP2 scorch-protected peroxide (with a di(tert-butylperoxy isopropyl)benzene active substance), made by Arkena, was added to the HNBR-based rubber compound 2. The composition of the applied HNBR-based rubber compound was different from the one specified in Examples 1 and 2 in that a different peroxide was applied for cross-linking. The manufacturing of the flexible pipe was then continued in a conventional manner, by laying rubberized textile layers 3, a cable embedding rubber layer 5, and six steel cable reinforcing plies 4. Then, additional rubberized textile layers 3 and a rubber cover 6 were laid on the steel cable reinforcing plies 4. Finally, the flexible pipe was vulcanized at 160 C.

(15) Upon dissecting the flexible pipe, adhesion between the PVDF liner 1 and the HNBR-based rubber layer 2 was examined. What was found was so-called cohesive failure, implying that the PVDF remained covered with rubber over the entire surface, the adhesion value being above 15 N/mm measured according to the ISO 36 standard.

(16) The advantage of the flexible pipe according to the invention is, therefore, that it is resistant to the effects of chemicals, such as the strong acids (formic acid, acetic acid, hydrochloric acid, hydrofluoric acid) and zinc bromide solution that are applied for treating oil wells. Zinc bromide chemically attacks hydrogenated nitrile butadiene rubber (HNBR), and thus the application of flexible pipes having a HNBR liner is severely restricted with zinc bromide. However, in the flexible pipe according to the invention the conveyed medium, does not come in contact with HNBR, and thus the pipe is capable of carrying zinc bromide solution.

(17) Hoses with a PVDF liner, when applied by way of example for well testing or for oil production applications, have much longer service life compared for example to hoses with polyamide 11 liner that are widely applied in the industry. In addition to that, thanks to the characteristics of the liner, flexible pipes with a PVDF liner are also gas decompression-resistant.

(18) The above advantages can be provided without etching or a treatment with adhesion-promoter solutions in order to provide adhesion between the liner and the HNBR-based rubber compound.

ADDITIONAL EXAMPLE COMPRISING PVDF HOMOPOLYMER

(19) A PVDF homopolymer sheet with a thickness of 1.7 mm was procured. The melting range of the applied PVDF material is 170-174 C. according to the manufacturer's data. Three 0.9-mm-thick layers of HNBR-based uncured rubber compound were laid on the PVDF sheet, together with two other 0.9-mm-thick layers of polychloroprene-based rubber compound. The HNBR compound had the same composition as the one presented in Example 1 of this specification. At a portion of both sides of the surface silicone paper separator sheet was applied between the HNBR and the PVDF. The laminate thus prepared was vulcanized at 175 C. for 40 minutes in an electrically heated press. Adhesion between the PVDF and HNBR inside the vulcanized laminate was above 20 N/mm as measured according to the ISO 36 standard.