(19)
(11)EP 2 548 996 B1

(12)EUROPEAN PATENT SPECIFICATION

(45)Mention of the grant of the patent:
29.04.2020 Bulletin 2020/18

(21)Application number: 12176983.0

(22)Date of filing:  18.07.2012
(51)International Patent Classification (IPC): 
F16L 58/18(2006.01)
F16L 58/08(2006.01)
F16L 59/147(2006.01)
F16L 13/02(2006.01)
F16L 57/00(2006.01)
F16L 58/14(2006.01)
F16L 59/20(2006.01)
C23C 28/00(2006.01)

(54)

Metal dusting protection for welded pipe assemblies

Metal-Dusting-Schutz für geschweißte Rohranordnungen

Protection contre la poussière de métal pour assemblages de tuyaux soudés


(84)Designated Contracting States:
AL AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HR HU IE IS IT LI LT LU LV MC MK MT NL NO PL PT RO RS SE SI SK SM TR

(30)Priority: 18.07.2011 US 201161508814 P
05.08.2011 US 201113204110

(43)Date of publication of application:
23.01.2013 Bulletin 2013/04

(73)Proprietor: AIR PRODUCTS AND CHEMICALS, INC.
Allentown, PA 18195-1501 (US)

(72)Inventors:
  • Dorsch, Larry Thomas
    Orefield, PA 18069 (US)
  • Licht, William Robert
    Allentown, PA 18103 (US)
  • Kerstetter, David R.
    Emmaus, PA 18049 (US)

(74)Representative: SSM Sandmair 
Patentanwälte Rechtsanwalt Partnerschaft mbB Joseph-Wild-Straße 20
81829 München
81829 München (DE)


(56)References cited: : 
EP-A2- 0 366 299
WO-A1-2005/019719
US-A1- 2005 005 983
WO-A1-2004/082824
WO-A1-2010/049667
  
      
    Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention).


    Description

    BACKGROUND



    [0001] The present invention relates to a method for protecting a welded pipe assembly from metal dusting and a welded pipe assembly suitable for performing the method. The present invention is useful for conveying gases comprising carbon monoxide at temperatures greater than 425°C while preventing metal dusting of the welded piping assembly.

    [0002] Corrosion by metal dusting is a significant problem for industrial processes in which gases comprising carbon monoxide are conveyed at elevated temperature. Under these conditions, the gas reacts with the metal pipe. The reaction may cause rapid pitting or general wastage of the pipe alloy. Carbon diffuses into the metal often with preferential diffusion paths along the grain boundaries. The carbon can cause the grains to separate from the bulk as a metal dust rich in carbon. This corrosion mechanism is also known as catastrophic carburization.

    [0003] Many industrial processes use or produce gases containing carbon monoxide. Production of these gases is typically done at elevated temperature. Examples include hydrogen or synthesis gas production by steam reforming, autothermal reforming, partial oxidation and gasification. Downstream of these production units the pipes may be subject to corrosion by metal dusting. Synthesis gas, also called syngas, is a mixture of hydrogen and carbon monoxide.

    [0004] Various solutions have been proposed in order to reduce metal dusting, including the use of surface coatings which increase the corrosion resistance of the pipes. For example the interior surfaces of the pipes may be aluminized in order to limit metal dusting.

    [0005] Effective aluminization is typically done by chemical vapor deposition at high temperature which results in a diffusion layer rich in aluminum on the surface of the material being coated. Fabricated components can be aluminized in this way, but there are some issues. One issue is that the size of component to be aluminized is limited by size of the furnace and the retort in which the component is to be placed. Larger furnaces and retorts are theoretically possible, but controlling the temperature uniformity necessary to achieve an effective coating becomes increasingly difficult and ultimately results in a practical limitation. Another issue is that components distort due to high temperature exposure which may limit the size and complexity of prefabricated components. So, there is a need to make final assembly of equipment in the field.

    [0006] Assembling the equipment by welding piping connections presents problems when the piping and/or equipment has been coated to protect against metal dusting. This is because the welding destroys the protection of the welded region and adversely affects the protection of the adjacent region.

    [0007] Industry desires methods for preventing metal dusting of welded pipe assemblies.

    [0008] Industry desires methods for preventing metal dusting of welded pipe assemblies that can be applied in the field.

    [0009] Industry desires welded pipe assemblies protected from metal dusting.

    [0010] Industry desires welded pipe assemblies protected from metal dusting that can be constructed in the field.

    [0011] A welded pipe assembly according to the preamble of claim 1 and a method for protecting a welded pipe assembly according to the preamble of claim 12 are known from WO 2004/082824 A1.

    [0012] US 3 965 555 A discloses a welded pipe assembly comprising two pipes and an inner lining to protect the pipes against erosion. The pipes are joined by means of a welded joint. To reduce the transfer of heat to the heat-degradable lining an insulating material is disposed between the welded joint and the inner lining.

    [0013] US 4 640 532 A discloses a welded pipe assembly comprising pipes welded to couplers. The pipes and couplers are covered with protective liners. An insulating material is disposed in a slot beneath the welded joint.

    [0014] Pipe assemblies and methods for joining pipes are furthermore known from EP 0 366 299 A2, WO 2005/01719 A1, WO 2010/049667 A1, US 2005/005983 A1, US 2 895 747 A, and US 3 575 445 A.

    BRIEF SUMMARY



    [0015] The solution for an improved metal dusting protection for welded pipe assemblies is provided by the welded pipe assembly according to claim 1 and the method according to claim 12. The dependent claims 2-11 and 13-15 provide preferred embodiments.

    [0016] The one or more retainers of claim 5 can in particular be metal.

    [0017] The backing ring of claim 6 can in particuclar be metal.

    [0018] In the welded pipe assembly according to claim 3 the weld material can be aluminum tolerant.

    [0019] In the welded pipe assembly according to claim 8
    the insulating material can at least partially be enclosed by a segment of the first pipe and a segment of the second pipe.

    [0020] In the welded pipe assembly according to claim 10 the first end portion of the first retainer can be attached to the first pipe by a second fluid tight welded joint and the first end portion of the second retainer can be attached to the second pipe by a third fluid tight welded joint.

    [0021] The first thermal insulation can be jacketed.

    [0022] The second thermal insulation can be jacketed.

    BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS



    [0023] 

    FIG. 1 illustrates a welded pipe assembly with abutted retainers.

    FIG. 2 illustrates a welded pipe assembly with overlapping retainers.

    FIG. 3 illustrates a welded pipe assembly with modified pipe ends.


    DETAILED DESCRIPTION



    [0024] The articles "a" and "an" as used herein mean one or more when applied to any feature in embodiments of the present invention described in the specification and claims. The use of "a" and "an" does not limit the meaning to a single feature unless such a limit is specifically stated. The article "the" preceding singular or plural nouns or noun phrases denotes a particular specified feature or particular specified features and may have a singular or plural connotation depending upon the context in which it is used. The adjective "any" means one, some, or all indiscriminately of whatever quantity. The term "and/or" placed between a first entity and a second entity means one of the first entity, (2) the second entity, and (3) the first entity and the second entity. The term "and/or" placed between the last two entities of a list of 3 or more entities means at least one of the entities in the list.

    [0025] The present invention relates to a method for protecting a welded pipe assembly from metal dusting and a welded pipe assembly suitable for performing the method. The welded pipe assembly comprises two pipes, weld material, and an insulating material that insulates the weld material from any hot gas conveyed through the welded pipe assembly. The present invention is particularly useful for conveying gases comprising carbon monoxide at temperatures greater than 425°C while preventing metal dusting of the welded piping assembly.

    [0026] Hot gas comprising CO is conveyed through the welded pipe assembly comprising a first pipe and a second pipe, the first pipe and the second pipe connected by a welded joint. The first pipe and the second pipe each have an exterior side and an interior side opposite the exterior side. The interior side of the first pipe and the interior side of the second pipe each have a barrier to carbon penetration (discussed below).

    [0027] Since the gases comprising carbon monoxide are conveyed at temperatures greater than 425°C, it is generally desirable to thermally insulate the piping system to minimize energy losses from the piping system.

    [0028] The method comprises thermally insulating the exterior side of the first pipe away from the welded joint and thermally exposing an area of the exterior side of the first pipe adjacent the welded joint.

    [0029] "Thermally insulating" and "thermally exposing" means that heat is removed at a faster rate from the thermally exposed exterior side of the pipe adjacent the welded joint than from the thermally insulated exterior side of the pipe away from the welded joint. Pipe may be thermally insulated by providing any form of thermal insulation to the pipe.

    [0030] The method also comprises thermally insulating the exterior side of the second pipe away from the welded joint and thermally exposing an area of the exterior side of the second pipe adjacent the welded joint.

    [0031] The method also comprises thermally exposing the exterior surface of the welded joint.

    [0032] The method also comprises thermally insulating the welded joint opposite the exposed exterior surface, a portion of the interior side of the first pipe adjacent the welded joint, and a portion of the interior side of the second pipe adjacent the welded joint with an insulating material. The insulating material may be a compliant insulating material.

    [0033] According to the method, in combination, the insulating material that thermally insulates the welded joint, the portion of the interior side of the first pipe, and the portion of the interior side of the second pipe, the exposed area of the exterior side of the first pipe, the exposed area of the exterior side of the second pipe, and the exposed exterior surface of the welded joint are sufficient to maintain a temperature of the exterior surface of the welded joint below 400°C, or below 350°C, or below 300°C. The skilled person can readily determine suitable combinations of insulating material and uninsulated exterior surface area required to maintain the temperature of the welded joint below the desired temperature (400°C, 350°C, or 300°C) for various expected temperature ranges for the conveyed gas and expected ambient conditions.

    [0034] The temperature of the exterior surface of the welded joint may be measured by any suitable technique, for example by an infrared thermometer, or contact thermocouple.

    [0035] The method may further comprise shielding the insulating material from the hot gas being conveyed through the pipes.

    [0036] The method may be carried out by the welded pipe assembles illustrated in the figures. The present invention also relates to the welded pipe assembly.

    [0037] The welded pipe assembly is described with reference to the figures, wherein like reference numbers refer to like elements through the several embodiments.

    [0038] The welded pipe assembly 1 comprises:

    a first pipe 10 having an exterior side 12 and an interior side 14 opposite the exterior side 12, the interior side of the first pipe 10 having a barrier to carbon penetration;

    a second pipe 20 having an exterior side 22 and an interior side 24 opposite the exterior side, the interior side of the second pipe 20 having a barrier to carbon penetration;

    a weld material forming a fluid tight welded joint 30 connecting an end 16 of the first pipe 10 to an end 26 of the second pipe 20; and

    an insulating material 50 in fixed spaced relation to the welded joint 30, the insulating material positioned to reduce heat transfer from any fluid passing through the first pipe 10 and the second pipe 20 to the welded joint 30.



    [0039] As used herein, an insulating material is any material that reduces heat transfer and has a bulk thermal conductivity less than 5 W/mK. The insulating material may have a bulk thermal conductivity less than 1 W/mK.

    [0040] The insulating material may be compliant. As used herein, compliant means not rigid and able to adapt to contraction and expansion of its surroundings without failing catastrophically. Examples of compliant insulating materials include insulation in the form of blankets, bats, modules, felt, paper and loose (bulk) fiber. These materials may be ceramic fiber, foams, or microporous insulation. These materials may also be adhesives or mastics and may be any combination of the above or may include fairly rigid components such as vacuum formed shapes or boards and compliant layers. Major manufacturers of such products include Thermal Ceramics and ANH Refractories. The insulating material may be a ceramic comprising one or more of SiO2, Al2O3, CaO, MgO, ZrO and Cr2O3.

    [0041] A person skilled in the art may select a suitable insulating material based on its bulk thermal conductivity, weight, plasticity, and/or other relevant properties. The required thickness of the insulating material may be calculated by the person skilled in the art based on, for example, the expected temperature and properties of the gas conveyed in the pipe, expected range of ambient conditions, and the desired temperature of the welded joint.

    [0042] As used herein, a pipe is any conduit or hollow body for conveying a fluid. The pipe may have a circular cross-section or any other suitable cross-section. Pipe is typically intended to have a round cross-section, but a certain degree of ovality is expected. The pipe may be produced by casting, extrusion, rolling and welding flat sheet, or by other known methods. The pipe may be straight, elbow-shaped, Tee-shaped, or other suitable shape. The pipe cross-section may increase or decrease over its length.

    [0043] The first pipe 10 and the second pipe 20 may be constructed from any metal or alloy suitable for the service in which it is employed. Those skilled in the art may readily select from various metals and alloys based on availability, cost, strength, chemical compatibility, etc. The first pipe and the second pipe may be constructed from stainless steels such as 304, 316 or 347. The first pipe and the second pipe may be constructed from higher grade alloys such as alloy 800 or 617 or from lower grade alloys such as ASTM materials A335 P11 or P22.

    [0044] As used herein, a weld material is any material suitable for forming a welded joint, such as welding wire. Since the article "a" means one or more when applied to any feature, one or more weld materials may be used to form the fluid tight welded joint. Any suitable weld material may be used that is appropriate for the pipe alloy and strength requirements. There may be additional limitations on the choice of weld material if the barrier coating is incorporated into the weld. As this method protects the weld and adjacent pipe material against metal dusting, the coating need not extend all the way to the weld bevel.

    [0045] The interior side of the first pipe may be aluminized to form the barrier to carbon penetration of the first pipe, and the interior side of the second pipe may be aluminized to form the barrier to carbon penetration of the second pipe.

    [0046] The aluminized surface may be formed by any known aluminizing technique. Aluminizing to form an aluminized surface includes chemical vapor deposition, cold spray, plasma spray, flame spray, and arc spray techniques.

    [0047] The barrier to carbon penetration of the first pipe may be a first diffusion coating and the barrier to carbon penetration of the second pipe may be a second diffusion coating. The first diffusion coating and the second diffusion coating may be the same type of diffusion coating. The diffusion coatings may comprise aluminum.

    [0048] As defined herein, and consistent with ASTM Designation B 875-96 (Reapproved 2008), a diffusion coating is one produced by causing an element to react with or diffuse into, or both, the surface of a metallic substrate, thus, chemically altering the surface of the substrate.

    [0049] A diffusion coating may also be called a diffusion alloy layer. The diffusion coating may be formed by chemical vapor deposition or other known process. For example, Endurance Technologies offers EndurAlon™, a diffusion alloying process that diffuses aluminum molecules directly into a substrate material.

    [0050] Any suitable barrier to carbon penetration may be used. The barrier may comprise one or more of chromium, silicon, aluminum, titanium, tin, and yttrium.

    [0051] The barrier to carbon penetration may be degraded or ruined in the heat affected zone near the welded joint from welding and/or preparation for welding. The barrier to carbon penetration of the first pipe may cover a portion of the of the interior side of the first pipe not covered by the insulating material. The barrier to carbon penetration of the second pipe may cover a portion of the of the interior side of the second pipe not covered by the insulating material.

    [0052] The welded pipe assembly may further comprise a backing ring 40 proximate the welded joint 30, the backing ring 40 having a face wherein the face contacts a portion of the interior side 14 of the first pipe 10 and also contacts a portion of the interior side 24 of the second pipe 20. Any suitable backing ring may be used. The backing ring may be metal and constructed from any suitable metal known in the art. The backing ring, if used, is positioned to facilitate forming of the welded joint without porosity.

    [0053] The welded pipe assembly may further comprise one or more retainers 60, 70 holding the insulating material 50 in place. The one or more retainers 60, 70 may be metal. The one or more retainers may also act as a shield or barrier to hinder process gas from contacting the insulating material, backing ring and/or weld material. The one or more retainers may help prevent erosion and/or abrasion of the insulating material. The insulating material is at least partially enclosed by the one or more retainers, a segment of the first pipe, a segment of the second pipe, and the optional backing ring, if present.

    [0054] The one or more retainers may be positioned to shield or provide a barrier to the heat-affected zones of the first pipe and the second pipe adjacent to the welded joint. The section of pipe adjacent the welded joint is heated during welding and is referred to as the heat-affected zone. The heat-affected zone, or portion thereof, is often cleaned prior to the welding operation. The heating and/or cleaning may affect the properties of the surface of the pipe in the heat-affected zone. For example, if the pipe is coated or aluminized, the heating and/or cleaning may adversely affect the coating or surface properties resulting in reduced protection from metal dusting. Proper positioning of the insulation provides the technical effect preventing any adverse effect of degraded surface properties due to heating and/or cleaning prior to welding.

    [0055] When the barrier to carbon penetration comprises aluminum, the weld material is preferably aluminum tolerant. An aluminum tolerant weld material is any weld material that when interfused with aluminum does not crack in service. Suitable weld materials include and may be selected from one or more of Inconel® 53MD, Inconel® 52, Inconel® 52M, Inconel® 152, Inconel®72, Inconel®72M, Inconel® 117, and Inconel®617.

    [0056] In case the retainers 60 and 70 do not act as a shield or barrier to hinder process gas from contacting the insulating material, optional backing ring, and/or weld material, the welded pipe assembly may further comprise a separate shield (not shown in the figures). The shield, if present, is in fixed spaced relation to the welded joint. The insulating material is at least partially enclosed by a segment of the first pipe, a segment of the second pipe, the optional backing ring, if present, and the shield, if present.

    [0057] To facilitate maintaining the exterior surface of the welded joint below 400°C, the exterior side 12 of the segment of pipe 10 may be uninsulated, the exterior side 22 of the segment of pipe 20 may be uninsulated, and the exterior surface of the welded joint 30 may be uninsulated. The exterior surface of the welded joint is the surface facing away from the insulating material 50.

    [0058] To reduce heat losses from the welded pipe assembly, the welded pipe assembly may further comprise thermal insulation 80 disposed to thermally insulate the exterior side 12 of the first pipe 10 away from the welded joint 30 and thermal insulation 90 disposed to thermally insulate the exterior side 22 of the second pipe 20 away from the welded joint 30. The thermal insulation may be ceramic fiber blanket. a calcium silicate type product, or other suitable thermal insulation known in the art.

    [0059] Thermal insulation 80 and thermal insulation 90 may each be jacketed. The jacket may be thin gauge stainless steel or aluminum sheet wrapped around the insulation to protect the insulation from the weather.

    [0060] The combination of having thermal insulation on the first pipe 10 and second pipe 20 away from the welded joint, and having an insulating material 50 positioned to reduce heat transfer from any fluid passing through the pipes to the welded joint 30, while the exterior side 12 of a segment of pipe 10 adjacent the welded joint 30 is uninsulated (i.e. the exposed area of the first pipe), the exterior side 22 of the second pipe 20 adjacent the welded joint 30 is uninsulated (i.e. the exposed area of the second pipe), and the exterior surface of the welded joint is uninsulated (i.e. the exposed exterior surface of the welded joint) can provide the method requirement to maintain the temperature of the exterior surface of the welded joint below 400°C.

    [0061] The gap between insulation 80 on the exterior side of pipe 10 and insulation 90 on the exterior side of pipe 20 may have a length ranging from 50 mm to 1000 mm.

    [0062] The length of the insulating material 50 may range from 50 mm to 1000 mm. The length corresponds to the lengthwise dimension of the pipes.

    [0063] The interior and exterior insulated zones may overlap or there may be a gap between the two.

    [0064] FIG. 1 shows a welded pipe assembly where the retainers are abutted. The first retainer 60 holds a first portion of the insulating material 50 and the second retainer 70 holds a second portion of the insulating material 50. The first retainer 60 has a first end portion 62 and a second end portion 64. The first end portion 62 of the first retainer 60 is attached to the first pipe 10. The second retainer 70 has a first end portion 72 and a second end portion 74. The first end portion 72 of the second retainer 70 is attached to the second pipe 20. The second end portion 64 of the first retainer 60 abuts against the second end portion 74 of the second retainer 70.

    [0065] FIG. 2 shows a welded pipe assembly where the retainers are overlapping. The first retainer 60 holds a first portion of the insulating material 50 and the second retainer 70 holds a second portion of the insulating material 50. The first retainer 60 has a first end portion 62 and a second end portion 64. The first end portion 62 of the first retainer 60 is attached to the first pipe 10. The second retainer 70 has a first end portion 72 and a second end portion 74. The first end portion 72 of the second retainer 70 is attached to the second pipe 20. The second end portion 64 of the first retainer 60 overlaps the second end portion 74 of the second retainer 70.

    [0066] FIG. 3 shows a welded pipe assembly with modified pipe ends. FIG. 3 shows the overlapping retainers 60 and 70, however, the modified pipe ends can also be used with abutting retainers. The pipe ends may be flared or otherwise modified as shown, so that the internal insulation does not obstruct the flow of the gas in the pipes.

    [0067] In any of the welded pipe assemblies shown in the figures, the first retainer 60 may be attached to the first pipe 10 by several tack welds, a full circumference filet weld, press fit, or any suitable attachment means.

    [0068] A full circumference filet weld provides the benefit of forming a seal to keep the process gas from getting behind the retainers and blowing the insulating material out of the retainer. Since the internal filet welds attaching the retainers are exposed to the process gas at the process gas temperature, the internal filet welds will be subject to metal dusting. The retainer may be installed with a full circumferential filet weld and aluminized along with the interior of the pipe to protect it from metal dusting. Alternatively these welds may be protected by maintaining the temperature of these welds below their metal dusting temperature by providing a combination of interior and exterior insulation resulting in cooler temperatures and low metal dusting rates. The retainers may be full "cylinders" so that until the internal filet weld is completely deteriorated, the retainer cannot be blown downstream away from the welded joint. Further, the insulating material may be tightly packed between the retainers and the pipes so that the process gas will not flow through the tightly packet insulating material, since the process gas will tend to follow the path of least flow resistance.

    [0069] In accord with the full circumference filet weld, the first end portion 62 of the first retainer may be attached to the first pipe 10 by a fluid tight welded joint 66 and the first end portion 72 of the second retainer 70 may be attached to the second pipe 20 by a fluid tight welded joint 76.

    [0070] As shown in FIG. 1 and FIG. 2, the first retainer 60 may have a wall portion 68 converging inward from the first end portion 62 of the first retainer 60.

    [0071] As shown in FIG. 1 and FIG. 2, the second retainer 70 may have a wall portion 78 diverging outward toward the first end of the second retainer 70.

    Examples



    [0072] A welded pipe assembly closely resembling FIG. 2 was fabricated and tested. The pipe diameter was about 35 cm. The insulating material on the inside of the pipe was ceramic fiber insulation with a thickness of about 2 cm. The length of the internally insulated zone was about 20 cm.

    [0073] The temperatures of the exterior surface of the pipes were measured using an infrared thermometer on the uninsulated weld, an uninsulated area slightly upstream of the weld, and an uninsulated area slightly downstream of the weld. The temperature was measured at 4 positions around the circumference: the 12 o'clock position (top), 3 o'clock position, 6 o'clock position, and 9 o'clock position.

    [0074] Table 1 shows the measured temperatures for a first welded pipe assembly. The temperatures of the gas flowing though the welded pipe assembly was about 570°C.

    [0075] The results show that the temperature of the pipe, particularly the temperature of the weld can be maintained below 400°C.
    Table 1
    positionTTT
     downstream (°C)weld (°C)upstream (°C)
    12 o'clock 307 163 240
    3 o'clock 306 169 267
    6 o'clock 317 143 281
    9 o'clock 243 131 242



    Claims

    1. A welded pipe assembly comprising:

    a first pipe (10) having an exterior side and an interior side opposite the exterior side, the interior side of the first pipe having a barrier to carbon penetration;

    a second pipe (20) having an exterior side and an interior side opposite the exterior side, the interior side of the second pipe having a barrier to carbon penetration;

    the first pipe (10) and the second pipe (20) being constructed from a metal or alloy;

    a weld material forming a fluid tight welded joint (30) connecting an end (16) of a segment of the first pipe (10) to an end (26) of a segment of the second pipe (20); and

    an insulating material (50) in fixed spaced relation to the welded joint (30), the insulating material positioned to reduce heat transfer from any fluid passing through the first pipe (10) and the second pipe (20) to the welded joint (30);

    wherein the exterior side of the segment of the first pipe (10) is uninsulated, the exterior side of the segment of the second pipe (20) is uninsulated, and an exterior surface of the welded joint (30) is uninsulated;
    characterized in that

    the insulating material (50) is at least partially enclosed by the segment of the first pipe (10) and the segment of the second pipe (20);

    a first thermal insulation (80) is disposed to thermally insulate the exterior side of the first pipe (10) away from the welded joint (30); and

    a second thermal insulation (90) is disposed to thermally insulate the exterior side of the second pipe (20) away from the welded joint (30).


     
    2. The welded pipe assembly according to claim 1 wherein the insulating material is compliant.
     
    3. The welded pipe assembly of claim 1 or claim 2 and one of the following features:

    (i) the interior side of the first pipe (10) is aluminized to form the barrier to carbon penetration of the first pipe, and the interior side of the second pipe (20) is aluminized to form the barrier to carbon penetration of the second pipe;

    (ii) the barrier to carbon penetration of the first pipe (10) is a first diffusion coating and the barrier to carbon penetration of the second pipe (20) is a second diffusion coating, the first diffusion coating preferably comprising aluminum and the second diffusion coating preferably comprising aluminum;

    (iii) the barrier to carbon penetration of the first pipe (10) is formed by a material deposited by chemical vapor deposition and the barrier to carbon penetration of the second pipe (20) is formed by a material deposited by chemical vapor deposition.


     
    4. The welded pipe assembly of any one of the preceding claims wherein the insulating material (50) is a ceramic fiber, preferably comprising one or more of SiO2, Al2O3, CaO, MgO, ZrO, and Cr2O3, or a foam or a microporous insulation.
     
    5. The welded pipe assembly of any one of the preceding claims further comprising:
    one or more retainers (60, 70) holding the insulating material (50) in place.
     
    6. The welded pipe assembly of any one of the preceding claims further comprising:
    a backing ring (40) proximate the welded joint (30), the backing ring having a face wherein the face contacts a portion of the interior side of the first pipe (10) and also contacts a portion of the interior side of the second pipe (20).
     
    7. The welded pipe assembly of any one of the preceding claims wherein the weld material is selected from at least one of Inconel® 53MD, Inconel® 52, Inconel® 52M, Inconel® 152, Inconel® 72, Inconel® 72M, Inconel® 117, and Inconel® 617, and wherein the weld material is different than the alloy of the first pipe (10) and different than the alloy of the second pipe (20).
     
    8. The welded pipe assembly of any one of the preceding claims further comprising:
    a shield in fixed spaced relation to the welded joint (30), wherein the insulating material (50) is at least partially enclosed by the backing ring (40), if present, and the shield.
     
    9. The welded pipe assembly of any one of the preceding claims wherein the insulating material (50) is at least partially enclosed by the one or more retainers (60, 70), if present, and the backing ring (40), if present.
     
    10. The welded pipe assembly of claim 5 or claim 9, wherein the one or more retainers comprise a first retainer (60) holding a first portion of the insulating material (50), and a second retainer (70) holding a second portion of the insulating material (50),
    wherein the first retainer (60) has a first end portion and a second end portion, the first end portion of the first retainer attached to the first pipe (10), preferably by a second fluid tight welded joint,
    wherein the second retainer (70) has a first end portion and a second end portion, the first end portion of the second retainer attached to the second pipe (20), perferably by a third fluid tight welded joint, and
    wherein the second end portion of the first retainer (60) abuts against or overlaps the second end portion of the second retainer (70).
     
    11. The welded pipe assembly of claim 10 and at least one of the following features:

    (i) the first retainer (60) has a wall portion converging inward from the first end portion of the first retainer;

    (ii) the second retainer (70) has a wall portion diverging outward toward the first end of the second retainer.


     
    12. A method for protecting a welded pipe assembly from metal dusting when conveying a gas comprising CO at a temperature greater than 425°C through a first pipe (10) and a second pipe (20), the first pipe and the second pipe connected by a welded joint (30), the first pipe having an exterior side and an interior side opposite the exterior side, the interior side of the first pipe having a barrier to carbon penetration, the second pipe having an exterior side and an interior side opposite the exterior side, the interior side of the second pipe having a barrier to carbon penetration, the welded joint having an exterior surface, the method comprising:

    thermally exposing the exterior surface of the welded joint; and
    characterized by

    thermally insulating the exterior side of the first pipe away from the welded joint and thermally exposing an area of the exterior side of the first pipe adjacent the welded joint;

    thermally insulating the exterior side of the second pipe away from the welded joint and thermally exposing an area of the exterior side of the second pipe adjacent the welded joint;

    thermally insulating the welded joint opposite the exposed exterior surface, a portion of the interior side of the first pipe adjacent the welded joint, and a portion of the interior side of the second pipe adjacent the welded joint with an insulating material (50);

    wherein, in combination, the insulating material, the exposed area of the exterior side of the first pipe, the exposed area of the exterior side of the second pipe, and the exposed exterior surface of the welded joint are sufficient to maintain a temperature of the exterior surface of the welded joint below 400°C.


     
    13. The method of claim 12 further comprising:
    shielding the insulating material from the gas.
     
    14. The method of claim 12 or claim 13 wherein the insulating material is compliant.
     
    15. The method of any one of claims 12 to 14
    wherein

    (i) the interior side of the first pipe (10) is aluminized to form the barrier to carbon penetration of the first pipe, and the interior side of the second pipe (20) is aluminized to form the barrier to carbon penetration of the second pipe;

    (ii) the barrier to carbon penetration of the first pipe (10) is a first diffusion coating and the barrier to carbon penetration of the second pipe (20) is a second diffusion coating, the first diffusion coating preferably comprising aluminum and the second diffusion coating preferably comprising aluminum;

    (iii) the barrier to carbon penetration of the first pipe (10) is formed by chemical vapor deposition and the barrier to carbon penetration of the second pipe (20) is formed by chemical vapor deposition.


     


    Ansprüche

    1. Ein geschweißter Rohrleitungsverbund umfassend:

    ein erstes Rohr (10) umfassend eine Außenseite und eine der Außenseite gegenüberliegende Innenseite, wobei die Innenseite des ersten Rohrs (10) eine Barriere gegen das Eindringen von Kohlenstoff aufweist,

    ein zweites Rohr (20) umfassend eine Außenseite und eine der Außenseite gegenüberliegende Innenseite, wobei die Innenseite des zweiten Rohrs (20) eine Barriere gegen das Eindringen von Kohlenstoff aufweist,

    wobei das erste Rohr (10) und das zweite Rohr (20) aus Metall oder einer Legierung hergestellt sind,

    ein Schweißmaterial, welches einen fluiddichte Schweißverbindung (30) bildet, welche ein Ende (16) eines Abschnitts des ersten Rohrs (10) und ein Ende (26) eines Abschnitts des zweiten Rohrs (20) miteinander verbindet, und

    ein Isolationsmaterial (50) in fester Abstandsrelation zu der Schweißverbindung (30), wobei das Isolationsmaterial (50) so positioniert ist, dass eine Wärmeübertragung zwischen einem Fluid, welches durch das erste Rohr (10) und das zweite Rohr (20) strömt, und der Schweißverbindung (30) reduziert wird,

    wobei die Außenseite des Abschnitts des ersten Rohrs (10), die Innenseite Abschnitts weiteren (20) und die Außenseite der Schweißverbindung (30) nicht isoliert sind;
    dadurch gekennzeichnet, dass

    das Isolationsmaterial (50) wenigstens teilweise von dem Abschnitt des ersten Rohrs (10) und dem Abschnitt des zweiten Rohrs (20) umschlossen ist,

    eine erste thermische Isolation (80) zur Wärmeisolierung der Außenseite des ersten Rohrs (10) abseits der Schweißverbindung (30) vorgesehen ist, und

    eine zweite thermische Isolation (90) zur Wärmeisolation der Außenseite des zweiten Rohrs (20) abseits der Schweißverbindung (30) gesehen ist.


     
    2. Geschweißter Rohrleitungsverbund nach Anspruch 1, wobei das Isolationsmaterial (50) nachgiebig ist.
     
    3. Geschweißter Rohrleitungsverbund nach Anspruch 1 oder Anspruch 2 und einem der folgenden Merkmale:

    (i) die Innenseite des ersten Rohrs (10) ist aluminiert, um die Barriere gegen das Eindringen von Kohlenstoff des ersten Rohrs zu bilden, und die Innenseite des zweiten Rohrs (20) ist aluminiert, um die Barriere gegen das Eindringen von Kohlenstoff des zweiten Rohrs zu bilden,

    (ii) die Barriere gegen das Eindringen von Kohlenstoff des ersten Rohrs (10) ist eine erste Diffusionsbeschichtung und die Barriere gegen das Eindringen von Kohlenstoff des zweiten Rohrs (20) ist eine zweite Diffusionsbeschichtung, wobei die erste Diffusionsbeschichtung vorzugsweise Aluminium enthält und die zweite Diffusionsbeschichtung vorzugsweise Aluminium enthält,

    (iii) die Barriere gegen das Eindringen von Kohlenstoff des ersten Rohrs (10) wird von einem , Material gebildet, welches durch chemische Gasphasenabscheidung aufgebracht wird, und die Barriere gegen das Eindringen von Kohlenstoff des zweiten Rohrs (20) wird von einem Material gebildet, welches durch chemische Gasphasenabscheidung aufgebracht.


     
    4. Geschweißter Rohrleitungsverbund nach einem der vorhergehenden Ansprüche, wobei das Isolationsmaterial (50) eine Keramikfaser, vorzugsweise wenigstens eines aus SiO2, Al2O3, CaO, MgO, ZrO und Cr2O3 umfassend, oder ein Schaum oder eine mikroporöse Isolation ist.
     
    5. Geschweißter Rohrleitungsverbund nach einem der vorhergehenden Ansprüche zusätzlich umfassend:
    wenigstens einen Halter (60,70), der das Isolationsmaterial (50) vor Ort hält.
     
    6. Geschweißter Rohrleitungsverbund nach einem der vorhergehenden Ansprüche zusätzlich umfassend:

    einen an die Schweißverbindung (30) angrenzenden Losflansch (40), welcher eine Oberfläche aufweist,

    wobei die Oberfläche in Kontakt mit einem Teil der Innenseite des ersten Rohrs (10) und ebenfalls ein Kontakt mit einem Teil der Innenseite des zweiten Rohrs (20) ist.


     
    7. Geschweißter Rohrleitungsverbund nach einem der vorhergehenden Ansprüche, wobei das Schweißmaterial aus einem aus Inconel® 53MD, Inconel® 52, Inconel®52 M, Inconel® 152, Inconel® 72, Inconel® 72M, Inconel®117 und Inconel® 617 gewählt ist, und wobei das Schweißmaterial von der Legierung des ersten Rohrs (10) verschieden ist und von der Legierung des zweiten Rohrs (20) verschieden ist.
     
    8. Geschweißter Rohrleitungsverbund nach einem der vorhergehenden Ansprüche zusätzlich umfassend:
    einen Schutz in fester Abstandsrelation zu der Schweißverbindung (30), wobei das Isolationsmaterial (50) zumindest teilweise von dem Losflansch (40), falls vorhanden, und dem Schutz umschlossen wird.
     
    9. Geschweißter Rohrleitungsverbund nach einem der vorhergehenden Ansprüche, wobei das Isolationsmaterial (50) zumindest teilweise von dem wenigstens einen Halter (60,70), falls vorhanden, und dem Losflansch (40), falls vorhanden, umschlossen wird.
     
    10. Geschweißter Rohrleitungsverbund nach Anspruch 5 oder Anspruch 9, wobei der wenigstens eine Halter (60, 70) einen ersten Halter (60), welcher einen ersten Teil des Isolationsmaterials (50) hält, und einen zweiten Halter (70), welcher einen zweiten Teil des Isolationsmaterials (50) hält, umfasst,
    wobei der erste Halter (60) einen ersten Endabschnitt und einen zweiten Endabschnitt aufweist und der erste Endabschnitt des ersten Halters (60) mit dem ersten Rohr (10), vorzugsweise über eine zweite fluiddichte Schweißverbindung, verbunden ist,
    wobei der zweite Halter (70) einen ersten Endabschnitt und einen zweiten Endabschnitt aufweist und der erste Endabschnitt des zweiten Halters mit dem zweiten Rohr (20) zu, vorzugsweise über eine dritte Fluiddichte Schweißverbindung, verbunden ist,
    wobei der zweite Endabschnitt des ersten Halters (60) an den zweiten Endabschnitt des zweiten Halters (70) anstößt oder mit diesem überlappt.
     
    11. Geschweißter Rohrleitungsverbund nach Anspruch 10 und wenigstens einem der folgenden Merkmale:

    (i) der erste Halter (60) umfasst einen Wandabschnitt, der vom ersten Endabschnitt des ersten Halters nach innen konvertiert,

    (ii) der zweite Halter (70) umfasst einen Wandabschnitt, der in Richtung des ersten Endes des zweiten Halters nach außen divergiert.


     
    12. Verfahren zum Schutz eines geschweißten Rohrleitungsverbundes vor Metal Dusting wenn ein CO enthaltendes Gas bei einer Temperatur größer 425 °C durch ein erstes Rohr (10) und ein zweites Rohr (20) geleitet wird, das erste Rohr und das zweite Rohr über eine Schweißverbindung (30) verbunden sind, das erste Rohr eine Außenseite und eine der Außenseite gegenüberliegende Innenseite aufweist, die Innenseite des ersten Rohrs eine Barriere gegen das Eindringen Kohlenstoff aufweist, das zweite Rohr eine Außenseite und eine der Außenseite gegenüberliegende Innenseite aufweist, die Innenseite des zweiten Rohrs eine Barriere gegen das Eindringen von Kohlenstoff aufweist, die Schweißverbindung eine äußere Oberfläche aufweist, das Verfahren umfasst:

    eine thermische Beanspruchung der äußere Oberfläche der Schweißverbindung, und gekennzeichnet durch

    eine thermische Isolation der Außenseite des ersten Rohrs abseits der Schweißverbindung und eine thermische Beanspruchung eines Bereichs der Außenseite des ersten Rohrs angrenzend an die Schweißverbindung;

    eine thermische Isolation der Außenseite des zweiten Rohrs abseits der Schweißverbindung und eine thermische Beanspruchung eines Bereichs der Außenseite des zweiten Rohrs angrenzend an die Schweißverbindung;

    eine thermische Isolation der Schweißverbindung gegenüber der beanspruchten äußeren Oberfläche, eines Teils der Innenseite des ersten Rohrs angrenzend an die Schweißverbindung, und eines Teils der Innenseite des zweiten Rohrs angrenzend an die Schweißverbindung mit einem Isolationsmaterial (50);

    wobei das Isolationsmaterial, der beanspruchte Bereich der Außenseite des ersten Rohrs, der beanspruchte Bereich der Außenseite des zweiten Rohrs, und die beanspruchte äußere Oberfläche der Schweißverbindung in Kombination ausreichend sind eine Temperatur der äußeren Oberfläche der Schweißverbindung unter 400 °C zu halten.


     
    13. Verfahren nach Anspruch 12 zusätzlich umfassend:
    eine Abschirmung des Isolationsmaterials von dem Gas.
     
    14. Verfahren nach Anspruch zwölf oder Anspruch 13, wobei das Isolationsmaterial nachgiebig ist.
     
    15. Verfahren nach einem der Ansprüche 12 bis 14,
    wobei

    (i) Losflansch (40) die Innenseite des ersten Rohrs (10) aluminiert ist, um die Barriere gegen das Eindringen von Kohlenstoff des ersten Rohrs zu bilden, und die Innenseite des zweite Rohrs (10) aluminiert ist, um die Barriere gegen das Eindringen von Kohlenstoff des zweiten Rohrs zu bilden,

    (ii) die Barriere gegen das Eindringen von Kohlenstoff des ersten Rohrs (10) ist eine erste Diffusionsbeschichtung und die Barriere gegen das Eindringen von Kohlenstoff des zweiten Rohrs (20) ist eine zweite Diffusionsbeschichtung, wobei die erste Diffusionsbeschichtung vorzugsweise Aluminium enthält und die zweite Diffusionsbeschichtung vorzugsweise Aluminium enthält,

    (iii) die Barriere gegen das Eindringen von Kohlenstoff des ersten Rohrs (10) durch chemische Gasphasenabscheidung gebildet wird, und die Barriere gegen das Eindringen von Kohlenstoff des zweiten Rohrs (20) durch chemische Gasphasenabscheidung gebildet wird.


     


    Revendications

    1. Un assemblage de tuyaux soudés comprenant :

    un premier tuyau (10) possédant une face extérieure et une face intérieure opposée à la face extérieure, la face intérieure du premier tuyau possédant une barrière à la pénétration de carbone ;

    un deuxième tuyau (20) possédant une face extérieure et une face intérieure opposée à la face extérieure, la face intérieure du deuxième tuyau ayant une barrière à la pénétration de carbone ;

    le premier tuyau (10) et le deuxième tuyau (20) étant composés d'un métal ou d'un alliage ;

    un matériau de soudage formant un joint soudé étanche aux fluides (30) raccordant une extrémité (16) d'un segment du premier tuyau (10) à une extrémité (26) d'un segment du deuxième tuyau (20) ; et

    un matériau isolant (50) dans une relation espacée fixe au joint soudé (30), le matériau isolant positionné pour réduire le transfert thermique d'un fluide traversant le premier tuyau (10) et le deuxième tuyau (20) vers le joint soudé (30) ;

    dans lequel la face extérieure du segment du premier tuyau (10) n'est pas isolée, la face extérieure du segment du deuxième tuyau (20) n'est pas isolée et une surface extérieure du joint soudé (30) n'est pas isolé;

    caractérisé en ce que

    le matériau isolant (50) est enveloppé, du moins en partie, par le segment du premier tuyau (10) et le segment du deuxième tuyau (20) ;

    une première isolation thermique (80) est disposée pour isoler thermiquement la face extérieure du premier tuyau (10) opposée au joint soudé (30) ; et

    une deuxième isolation thermique (90) est disposée pour isoler thermiquement la face extérieure du deuxième tuyau (20) opposé au joint soudé (30).


     
    2. L'assemblage de tuyaux soudés selon la revendication 1, dans lequel le matériau isolant est souple.
     
    3. L'assemblage de tuyaux soudés selon l'une des revendications 1 ou 2 présentant l'une des propriétés suivantes :

    (i) la face intérieure du premier tuyau (10) est aluminisée pour former la barrière à la pénétration de carbone du premier tuyau et la face intérieure du deuxième tuyau (20) est aluminisée pour former la barrière à la pénétration de carbone du deuxième tuyau ;

    (ii) la barrière à la pénétration de carbone du premier tuyau (10) est un premier revêtement de diffusion et la barrière à la pénétration de carbone du deuxième tuyau (20) est un deuxième revêtement de diffusion, le premier revêtement de diffusion comprenant de préférence de l'aluminium et le deuxième revêtement de diffusion comprenant de préférence de l'aluminium ;

    (iii) la barrière à la pénétration de carbone du premier tuyau (10) est formée par un matériau déposé par dépôt chimique en phase vapeur et la barrière à la pénétration de carbone du deuxième tuyau (20) est formée par un matériau déposé par dépôt chimique en phase vapeur.


     
    4. L'assemblage de tuyaux soudés selon l'une des revendications précédentes, dans lequel le matériau isolant (50) est une fibre céramique, composée de préférence d'un ou plusieurs des composés SiO2, Al2O3, CaO, MgO, ZrO et Cr2O3, d'une mousse ou d'une isolation microporeuse.
     
    5. L'assemblage de tuyaux soudés selon l'une des revendications précédentes comprenant par ailleurs : une ou plusieurs pièces de retenue (60, 70) maintenant le matériau isolant (50) en place.
     
    6. L'assemblage de tuyaux soudés selon l'une des revendications précédentes comprenant par ailleurs :
    une bague de support (40) proche du joint soudé (30), la bague de support ayant une face, dans laquelle la face entre en contact avec une partie de la face intérieure du premier tuyau (10) et est également en contact avec une partie de la face intérieure du deuxième tuyau (20).
     
    7. L'assemblage de tuyaux soudés selon l'une des revendications précédentes, dans lequel la matière de soudage est choisie parmi au moins un de Inconel® 53MD, Inconel® 52, Inconel® 52M, Inconel® 152, Inconel® 72, Inconel® 72M, Inconel® 117 et Inconel® 617, et dans lequel la matière de soudage est différente de l'alliage du premier tuyau (10) et différente de l'alliage du deuxième tuyau (20).
     
    8. L'assemblage de tuyaux soudés selon l'une des revendications précédentes comprenant par ailleurs un écran dans une relation espacée fixe par rapport au joint soudé (30), le matériau isolant (50) étant enfermé, du moins en partie, par la bague de support (40) éventuellement présente et l'écran.
     
    9. L'assemblage de tuyaux soudés selon l'une des revendications précédentes, dans lequel le matériau isolant (50) est renfermé, du moins en partie, par une ou plusieurs pièces de retenue (60, 70) éventuellement présentes, et la bague de support (40) éventuellement présente.
     
    10. L'assemblage de tuyaux soudés selon l'une des revendications 5 ou 9, dans lequel une ou plusieurs des pièces de retenue comprennent une première pièce de retenue (60) maintenant une première portion du matériau isolant (50) et une deuxième pièce de retenue (70) maintenant une deuxième portion du matériau isolant (50), dans lequel la première pièce de retenue (60) possède une première partie d'extrémité et une deuxième partie d'extrémité, la première partie d'extrémité de la première pièce de retenue étant fixée au premier tuyau (10), de préférence par un deuxième joint soudé étanche aux fluides, dans laquel la deuxième pièce de retenue (70) possède une première partie d'extrémité et une deuxième partie d'extrémité, la première partie d'extrémité de la deuxième pièce de retenue étant fixée au deuxième tuyau (20), de préférence par un troisième joint soudé étanche aux fluides, et dans lequel la deuxième partie d'extrémité de la première pièce de retenue (60) bute contre la deuxième partie d'extrémité de la deuxième pièce de retenue (70) ou la chevauche.
     
    11. L'assemblage de tuyaux soudés selon la revendication 10 et au moins l'une des propriétés suivantes : (i) la première pièce de retenue (60) possède une partie de paroi convergeant vers l'intérieur à partir de la première partie d'extrémité de la première pièce de retenue ; (ii) la deuxième pièce de retenue (70) possède une partie de paroi divergeant vers l'extérieur vers la première extrémité de la deuxième pièce de retenue.
     
    12. Un procédé de protection d'un assemblage de tuyaux soudés contre la poussière de métal lors du transport d'un gaz comprenant du CO à une température supérieure à 425°C par un premier tuyau (10) et un deuxième tuyau (20), les premier et deuxième tuyaux étant raccordés par un joint soudé (30), le premier tuyau ayant une face extérieure et une face intérieure opposée à la face extérieure, la face intérieure du premier tuyau ayant une barrière à la pénétration de carbone, le deuxième tuyau ayant une face extérieure et une face intérieure opposée à la face extérieure, la face intérieure du deuxième tuyau ayant une barrière à la pénétration de carbone, le joint soudé ayant une surface extérieure, le procédé comprenant : l'exposition thermique de la surface extérieure du joint soudé; et caractérisé par :

    l'isolation thermique de la face extérieure du premier tuyau opposée au joint soudé et l'exposition thermique d'une zone de la face extérieure du premier tuyau adjacente au joint soudé ; l'isolation thermique de la face extérieure du deuxième tuyau opposée au joint soudé et l'exposition thermique d'une zone de la face extérieure du deuxième tuyau adjacente au joint soudé;

    l'isolation thermique du joint soudé opposé à la surface extérieure exposée, une partie de la face intérieure du premier tuyau adjacente au joint soudé, une partie de la face intérieure du deuxième tuyau adjacente au joint soudé avec un matériau isolant (50),

    dans lequel le matériau isolant, combiné avec la zone exposée de la face extérieure du premier tuyau, la zone exposée de la face extérieure du deuxième tuyau et la surface extérieure exposée du joint soudé sont suffisant pour maintenir une température de la surface extérieure du joint soudé en dessous de 400° C.


     
    13. Le procédé selon la revendication 12, comprenant par ailleurs :
    la protection du matériau isolant contre le gaz.
     
    14. Le procédé selon la revendication 12 ou 13, dans lequel le matériau isolant est souple.
     
    15. Procédé selon l'une des revendications 12 à 14,
    dans lequel
    (i) la face intérieure du premier tuyau (10) est aluminisée pour former la barrière à la pénétration de carbone du premier tuyau et la face intérieure du deuxième tuyau (20) est aluminisée pour former la barrière à la pénétration de carbone du deuxième tuyau ; (ii) la barrière à la pénétration de carbone du premier tuyau (10) est un premier revêtement de diffusion et la barrière à la pénétration de carbone du deuxième tuyau (20) est un deuxième revêtement de diffusion, le premier revêtement de diffusion comprenant de préférence de l'aluminium et le deuxième revêtement de diffusion comprenant de préférence de l'aluminium ; (iii) la barrière à la pénétration de carbone du premier tuyau (10) est formée par un matériau déposé par dépôt chimique en phase vapeur et la barrière à la pénétration de carbone du deuxième tuyau (20) est formée par un matériau déposé par dépôt chimique en phase vapeur.
     




    Drawing











    Cited references

    REFERENCES CITED IN THE DESCRIPTION



    This list of references cited by the applicant is for the reader's convenience only. It does not form part of the European patent document. Even though great care has been taken in compiling the references, errors or omissions cannot be excluded and the EPO disclaims all liability in this regard.

    Patent documents cited in the description