WO2019175488A1 - Underwater transport pipeline for petroleum products and insulation method - Google Patents

Abstract

Pipeline for the underwater transport of petroleum products comprising an internal conduit (2) which is designed to contain the petroleum to be transported and an external conduit (4) which is arranged concentrically around the first conduit (2) with a space (5) between the two conduits (2, 4), wherein the space (5) between the two conduits (2, 4) is under a vacuum at a pressure between 0 and 1 bar, characterised in that the space (5) under a vacuum contains gas at a concentration in molar fractions of krypton greater than 70% and preferably greater than 80%.

Description

 Underwater petroleum transport pipeline and insulation process

The invention relates to a pipeline for submarine transport of petroleum products and an isolation process.

 More particularly, the invention relates to a pipe for the underwater transport of petroleum products comprising an inner pipe for containing the oil to be transported and an outer pipe arranged concentrically around the first pipe with a spacing between the two pipes, the spacing between the two lines being under vacuum at a pressure between 0 and 1 bara.

 It is known to use double jacketed pipes to transport crude oil under the sea between off-shore exploitation sites or between an off-shore site and the coast. The pipe is located under water at a temperature generally below 10 ° C. Some pipes or networks have a length that can reach several tens of kilometers.

The oil is extracted from the deposit at a temperature generally between 50 and 130 ° C and conveyed in a pipe via a pumping system. This oil must be kept at a temperature that prevents its solidification in the pipes. For this, (i) the internal pipe is generally heated and (ii) an air vacuum insulation is also provided between the inner pipe and the outer pipe by means of a pump. This vacuum evacuation operation is generally carried out during the installation of the underwater pipeline. Thus, it may be necessary to provide several hours for a vacuum pump to reach in the inter- conducted a vacuum of 10 to 20 mbar (bara = absolute bar) for a pipe of several hundred meters in length.

 These solutions are therefore complex, expensive and require in particular a large amount of electrical energy to maintain these temperatures.

 An object of the present invention is to overcome all or part of the disadvantages of the prior art noted above.

 For this purpose, the pipeline according to the invention, moreover, in accordance with the generic definition given in the preamble above, is essentially characterized in that the vacuum spacing contains gas having a molar fraction concentration of krypton. greater than 70% and preferably greater than 80%.

 Furthermore, embodiments of the invention may include one or more of the following features:

 the vacuum spacing is at a pressure of between 0.40 bara and 0.01 bara,

 the vacuum spacing is at a pressure of between 0.37 bara and 0.01 bara, in particular 0.05 bara,

 the first pipe is coated at least on its outer surface with a layer of a material with a reduced emissivity of between 0.05 and 0.2,

 the inner pipe has an emissivity of between 0.1 and 0.9, in particular between 0.3 and 0.9 and preferably between 0.1 and 0.5,

 the second pipe is coated at least on its inner surface with a layer with a reduced emissivity of between 0.05 and 0.2,

the external pipe has an emissivity of between 0.1 and 0.9, especially between 0.3 and 0.9 and preferably between 0.1 and 0.5, - The pipe comprising a heating member of the inner pipe.

 1 / invention also relates to a method of isolating at least one subsea oil transport and distribution pipe, the pipe comprising an inner pipe containing the oil to be transported and an outer pipe arranged concentrically around the first pipe with a spacing between the two pipes, the spacing between the two pipes being evacuated to a pressure between 0 and 1 bara, the vacuum space containing a gas having a krypton concentration greater than 70% and preferably greater than 80%.

 According to other possible features:

 the vacuuming of the spacing between the two pipes comprises a step of introducing krypton in the spacing between the two pipes initially containing a gas distinct from krypton at a pressure of less than 0.37 bar, in particular 0.01 bara the krypton being introduced into the spacing until reaching a pressure of 0.37 bara and 0.01 bara, in particular 0.05 bara,

 the evacuation of the spacing between the two pipes comprises a step of introducing krypton into the spacing between the two pipes initially containing a gas distinct from krypton at a pressure greater than 0.4 bar, in particular 1 bara, krypton being introduced into the gap until reaching a high pressure of between 1.2 and 20 bara, especially 10 bara, the introduction step being followed by a purge step of removing gas from the spacing until reaching a determined low pressure of between 0.37 bara and 0.01 bara, in particular 0.05 bara.

The invention may also relate to any device, network or alternative method comprising any combination of features above or below in the context of the claims.

 Other particularities and advantages will appear on reading the following description, made with reference to the figures in which:

 FIG. 1 represents a sectional view, schematic and partial, illustrating the structure of a pipe according to the invention,

 FIGS. 2 and 3 are schematic and partial sectional views illustrating the structure and operation of two possible embodiments of an insulation of a pipe according to FIG.

 Line 1 for submarine transport of oil illustrated in the figures comprises an inner pipe 2 for containing the oil to be transported and an outer pipe 4 concentrically disposed around the first pipe 2 with a spacing 5 between the two pipes 2, 4 .

The pipes 2, 4 may be composed of at least one of the following materials; steel, or other metal alloys. The pipe or conduits 2, 4 may be composed in particular of a steel having a conductivity of 50 Wm ^-1 .K ^-1 .

 The pipes 2, 4 may have diameters of between 20 and 60 cm for example.

 As illustrated in Figure 2, the pipe 1 may comprise a member 3 for heating the inner pipe 2, for example an electric heater.

 Conventionally, the spacing 5 between the two lines 2, 4 is under vacuum at a pressure between 0 and 1 bara.

According to an advantageous feature, the vacuum gas providing this thermal insulation is krypton or a mixture which has a molar fraction concentration of krypton greater than 70% and preferably greater than 80%, especially 90% or more (the rest can be air) . This improves the thermal insulation properties (convection and radiation) compared to known solutions where the spacing contains air.

 To further significantly improve the insulation, the inventors further determined that the pressure in the vacuum gap is preferably between 0.40 bara and 0.01 bara. This is greater than the pressure used in known solutions with air.

 In particular, the inventors have demonstrated that the pressure of the gas containing predominantly krypton in the vacuum space should preferably be less than 0.37 bara and advantageously equal to or close to 0.05 bara.

 These conditions significantly improve insulation, including convective losses even if the pressure in the spacing (0.37 to 0.01 bara for example) is higher than the pressure levels of the known systems (0.01bara). The pressure in the spacing may be between 0.37 and a low value that is greater than 0.010 bara. This low value is for example equal to 0.015, 0.020, 0.025, 0.030 or 0.035, 0.040, 0.045, 0.050 or 0.055 bara, for example).

 Thus, the use of a high proportion of krypton improves the isolation conditions. These isolation conditions are further improved for determined pressure levels in the spacing. This solution makes it possible to reduce the thermal losses and, if necessary, also reduce the vacuum levels required for the insulation.

 The depression of the spacing 5 can be easier and less expensive energy.

The thermal insulation is further improved if the emissivity of the pipe or conduits 2, 4 is as low as possible. This is achieved by minimizing the oxidation and the rough state of the surface of the pipe 2, for example by coating it a coat of paint with a low-emissivity coating, often based on aluminum, or by sticking a very bright aluminum foil on the wall.

 Preferably the emissivity of the outer surface of the inner pipe 2 and / or the inner surface of the outer pipe 4 is lowered between 0.05 and 0.20.

 For a pipe already under vacuum of air according to the prior art (pressure in the spacing of 0.01 bara for example), the insulation can be performed as follows (in connection with FIG. 2).

 Krypton from a source 6 can be introduced into the gap 5 between the two lines 2, 4 to reach a pressure of 0.37 bara and 0.01 bara, in particular 0.05 bara. This can be achieved by means of a pump 7 or any other suitable organ. Considering an emissivity of 0.1 for the pipes 2, 4, this modification of the composition and the pressure in the spacing 5 makes it possible to reduce by approximately 43% the thermal losses with respect to an equivalent solution of the art. prior.

 For a pipe 1 initially at atmospheric pressure in the spacing 5 (not isolated), the insulation can be made as follows (in connection with FIG. 3).

 Krypton 6 may be introduced into the gap 5 between the two lines 2, 4 containing air, for example 1 bara. The krypton is introduced into the spacing, for example via a pump 7 until reaching in the spacing a high pressure of between 2 and 20 bara, in particular 10 bara.

 Then, the gas of the space is purged (for example via a vacuum pump 8 until a determined low pressure of between 0.37 bara and 0.01 bara, in particular 0.05 bara, is reached. to be carried out in two stages:

1) decreasing the pressure in the spacing 5 to atmospheric pressure or near, 2) vacuum pumping.

 Considering also an emissivity of 0.1 for the lines 2 and 4, this modification of the composition and the pressure in the spacing 5 makes it possible to reduce by approximately 47% the thermal losses with respect to an equivalent solution of the prior art (even with a pressure 0.05 bara five times higher than the pressure 0.01 bara vacuum of the previous solution).

Claims

A pipeline for the underwater transport of petroleum products comprising an inner pipe (2) for containing the oil to be transported and an outer pipe (4) arranged concentrically around the inner pipe (2) with a spacing (5) between the two lines (2, 4), the spacing (5) between the two lines (2, 4) being under vacuum at a pressure of between 0 and 1 bara, characterized in that the vacuum spacing (5) contains gas having a mole fraction concentration of krypton greater than 70% and preferably greater than 80%, and in that the inner pipe (2) is coated at least on its outer surface with a layer of an emissivity material reduced between 0.05 and 0.2 and / or the outer pipe (4) is coated at least on its inner surface with a reduced emissivity layer between 0.05 and 0.2.  2. Sewer according to claim 1, characterized in that the spacing (5) under vacuum is at a pressure between 0.40 bara and 0.01 bara.  3. Sewer according to claim 1 or 2, characterized in that the spacing (5) under vacuum is at a pressure between 0.37 bara and 0.01 bara, including 0.05 bara.  4. Pipe according to any one of claims 1 to 3, characterized in that the pipe (2) has an internal emissivity of between 0.3 and 0.9 and preferably between 0.1 and 0.5. 5. Pipe according to any one of claims 1 to 4, characterized in that the pipe (1) comprising a member (3) for heating the inner pipe. 6. A method of isolating at least one underwater oil transport and distribution pipe, the pipe (1) comprising an inner pipe (2) containing the oil to be transported and an outer pipe (4) arranged concentrically around of the first pipe (2) with a spacing (5) between the two pipes (2, 4), the spacing (5) between the two pipes (2, 4) being evacuated to a pressure of between 0 and 1 bara, the vacuum space (5) containing a gas having a krypton concentration greater than 70% and preferably greater than 80%, and in that the inner pipe (2) is coated at least on its outer surface with a layer of a material with a reduced emissivity between 0.05 and 0.2, the outer pipe (4) is coated at least on its inner surface with a reduced emissivity layer of between 0.05 and 0.2.  7. Method according to claim 6, characterized in that the evacuation of the spacing (5) between the two lines (2, 4) comprises an introduction step (7) of krypton (6) in the spacing (5) between the two pipes (2, 4) initially containing a gas distinct from krypton at a pressure of less than 0.37 bar, in particular 0.01 bara, the krypton being introduced into the spacing until reaching a pressure thereon between 0.37 bara and 0.01 bara, in particular 0.05 bara. 8. Method according to claim 7, characterized in that the evacuation the spacing (5) between the two pipes (2, 4) comprises a step of introduction (7) krypton (6) in the spacing between the two pipes (2, 4) initially containing a gas distinct from krypton at a pressure greater than 0.4 bar, in particular 1 bara, the krypton being introduced into the space (5) until reaching a high pressure of between 2 and 20 bara, including 10 bara, the introduction step being followed by a purge step of removing (8) gas from the gap (5) until reaching a determined low pressure of between 0.37 bara and 0, 01 bara, especially 0.05 bara.