KR20100016156A - Offloading pipeline - Google Patents

Abstract

A system for transporting low temperature fluids comprising; a carrier pipe (2); and at least one inner product flow pipe (1) located within and thermally isolated from the carrier pipe (2); wherein the product pipe (1) has a greater length than the carrier pipe (2) and is incorporated into the entire length of the carrier pipe (2) by following a non-linear path, such that thermal contraction of the product pipe (1) due to a change in temperature of the product pipe (1) is accommodated by elastic geometric distortion of the product pipe (1).

Description

Unloading Pipeline

The present invention relates to a pipeline system for conveying low temperature fluids, such as liquefied natural gas (LNG). In particular, it relates to a pipeline system for transporting fluid along the seabed between an offshore terminal and an onshore facility.

Where large quantities of natural gas are produced, the general technique for transporting gas to remote markets is a specially designed, liquefied gas and mounted on a sailing vessel at a coastal location near the gas source. Conveying liquefied natural gas (LNG) in the storage tanks. To produce LNG, natural gas is compressed and cooled to cryogenic temperatures, ie -160 ° C, to increase the amount that can be transported in the storage tanks. When the vessel reaches its destination, LNG is unloaded into onshore storage tanks from which LNG can be vaporized again as needed and delivered to end users via pipelines and the like. When the seabed is gently shallowed from the shore, it is necessary to make room beneath the keels of large LNG tankers and to locate the loading / unloading facility away from the coastal environment to obtain health, safety, and / or environmental benefits. When necessary, it is desirable to position the LNG import or loading terminals far offshore.

Currently known cryogenic fluid delivery systems include systems installed in causeways or trestle jetties that are specially constructed between onshore tanks and offshore containment / loading facilities. Supporting LNG loading lines on these long causeways or docks is expensive. The brace should be sufficiently above water to exclude the conveying line from being exposed to water and in some cases to avoid disrupting existing sea traffic on the water surface. The cost associated with construction requires that the offshore facility be located close to the coast, which in turn requires dredging of new access channels and the construction of additional port facilities to ensure safe passage of LNG carriers with deep drafts. You can do In addition, a return line for circulating LNG during idle periods can be configured and insulated separately from the main transport line of the flow system, thereby significantly increasing the cost, complexity, and safety concerns of the transport system. You can. However, the cryogenic fluid delivery system submerged as a pipeline supported by the seabed allows the receiving / loading station to be located farther from the shore, and cause no causeway or brace unless the LNG vessels with deep drafts are operated. Dredging the necessity and access channels of the wharf and the construction of expensive port facilities and dredging the need and access channels for the causeway or brace wharf for operating deep draft LNG vessels in areas where it would not be necessary to build the dredging port facilities. Eliminate the need

The problem with the transport of cryogenic fluids in pipelines is that they generate significant thermal stress by causing the actual shrinkage of most pipe materials as the cold fluids enter the pipeline.

For fluid conveying systems located on the sea floor, an insulated "pipe for LNG loading / unloading to maintain the cryogenic temperature of the LNG carried with the annular space between the product pipe or pipes and the outer carrier pipe in vacuum It is desirable to have a "pipe-in-pipe" structure. Heat shrinkage of the product pipe may be accommodated through multiple and / or large expansion loops on a pipeline system supported by a bridge pier or causeway. Such pipeline systems with expansion loops are still generally linear and have right angles to join the bends with the linear product pipe. By having mostly linear pipelines in the system, the length of the product pipe still only inevitably changes when the temperature changes, and the heat shrinkage is due to the bends located along the product pipe to include the expansion loops. Local stresses may occur. In addition, the behavior of these expansion loops in the "pipe in pipe" structure in the sea on the sea floor can be limited by the silting, and these large expansion loops in the "pipe in pipe" pipeline in the sea Difficult to manufacture and install Alternatively, materials with very low coefficients of thermal expansion, such as INVAR ^™ (36% nickel steel), can be used to produce the fluid transport inner pipe, but this is relatively expensive.

It is an object of the present invention to accommodate the heat shrinkage of product pipes for fluid delivery systems in the sea. In particular, the present invention introduces an additional length of product pipe into a carrier pipe by forming a non-linear path such that there is a change in geometry and length substantially along the entire length of the product pipe when heat shrinkage occurs, thereby introducing additional A fluid delivery system for delivering cryogenic fluids between onshore facilities is provided.

A first aspect of the invention is a carrier pipe; And at least one internal product flow pipe located within the carrier pipe and insulated from the carrier pipe, wherein thermal shrinkage of the product pipe due to temperature change of the product pipe is accommodated by the elastic geometric deformation of the product pipe. Preferably the product pipe comprises a system for transporting cryogenic fluids, having a longer length than the carrier pipe and contained within the full length of the carrier pipe in a non-linear path.

Particularly preferred cryogenic fluids that the system can carry are cryogenic fluids, for example fluids having a temperature of about -160 ° C, such as LNG.

The extra length of the product pipe, which is longer than the carrier pipe, is received by another path along the product pipe through the carrier pipe. At approximately the same temperatures, such as before the flow of cryogenic fluid through the product pipe, the product pipe has a longer length than the carrier pipe, and the product pipe is never shorter than the carrier pipe when there is a change in temperature. When the product pipe is cooled by the introduction of cryogenic fluids, the change in the geometry of the product pipe, rather than only by a reduction in the length of the product pipe occurring in generally linear pipeline systems, and thus The shape of the product pipe differs from the shape of the carrier pipe before the flow of cryogenic fluid through the product pipe such that heat shrinkage is mainly accommodated by its path through the carrier pipe.

Preferably, the product pipe is insulated by vacuum over the carrier pipe. The vacuum is formed in the annular space between the carrier pipe and the product pipe.

Preferably, the non-linear path is a path that is generally continuous. The product pipe can follow a curved path substantially along its entire length with generally straight sections.

Generally nonlinear product pipes vary in the geometry and shape of the product pipes to accommodate heat shrinkage, rather than the only change in length found in generally linear pipeline systems undergoing heat shrinkage due to temperature changes. Will bring change. Having a product pipe that is continuously curved produces expansion loops in which heat shrinkage can generate local stresses at right angle bends that are present to have loops in the product pipe and also at intermediate bulkheads where these can be fitted. It will disperse stresses across the entire product pipe during thermal contraction as compared to including primarily linear pipeline systems.

Preferably, the product pipe has a regular shape such as a sinusoidal shape or a steep angle spiral shape before the product pipe is exposed to a change in temperature. This temperature change can be caused by the flow of cryogenic fluid through the product pipe.

Advantageously, the system comprises two or more product pipes located within said carrier pipe. This allows for a larger volume of fluid to be conveyed through the system.

The system may have spacers for supporting the product pipe. The spacers may be positioned to prevent the product pipe from being completely straight in the carrier pipe. Preferably, the spacers are located approximately every half of the wavelength of the product pipe configured in a planar wavelength shape.

Bulkheads may be attached to the ends of the carrier pipe and the product pipe. They may be located at each end of the pipes to form an insulated seal.

The system further includes valves for regulating flow through the product pipes such that recycling of product fluid takes place, for example, to maintain cryogenic temperatures in the casing pipe when no transport of LNG is performed.

The system further includes tapping through the carrier pipe to enable a vacuum to be formed in the carrier pipe. This enables a vacuum to be formed around the product pipe or pipes to prevent heat flow into the product causing an increase in its temperature.

1 shows a sinusoidal shaped product pipe in a carrier pipe at ambient temperature;

2 is a view of a single product pipe having a spiral shape in a carrier at ambient temperature;

3 is a top view of a fluid delivery system with four spirally shaped product pipes in a carrier pipe;

4 is a diagram illustrating a landside distal end of the fluid delivery system;

5 is a view showing the marine end portion of the fluid delivery system;

6 is a cross-sectional view of the fluid pipeline.

Preferred embodiments of the present invention are now described with reference to the drawings. Fluid delivery systems for transporting fluids, especially cryogenic fluids such as LNG, have a "pipe-in-pipe" structure comprising a product pipe 1 located within the carrier pipe 2. At each end of the pipe-in pipe structure, the bulkhead 6 device forms a sealed and insulated seal against the carrier pipe. 1 illustrates one embodiment of the present invention. The product pipe 1 of FIG. 1 has a sinusoidal shape, but the product pipe may comprise other similar regularly repeated shapes. The sinusoidal shape allows the extra length of the product pipe to be accommodated in a shorter carrier pipe. The product pipe is sine within the carrier pipe when the product pipe is at ambient temperature, i.e., before the flow of cryogenic fluid through the fluid delivery system, the product pipe and the carrier pipe are at substantially the same temperatures. In order to have a curved shape, the product pipe 1 may be previously formed into a sinusoidal shape by axial bucking or plastic deformation. When a cryogenic fluid such as LNG flows through the product pipe 1, the LNG cools the product pipe to thermally shrink the product pipe. The reduction in the length of the product pipe 1 when the product pipe 1 is cooled is mainly due to the straightening of the curve of the product pipe, rather than by the axial strain of the thermally induced material. It is accommodated by the change in shape to change the path of the product pipe passing through the carrier pipe. The product pipe will straighten within its elastic limits. If the product pipes were initially straightened, the reduction in the length going on would have been accommodated by the plastic axial strain. In addition to the change in the geometry of the product pipe, the product pipe may also change in length, but the length of the product pipe will never be shorter than the length of the carrier pipe. Straightening of the product pipe 1 when the product pipe 1 is cooled is aided by slots present in the support spacers 11. The spacers and slots are positioned so as not to allow the product pipe to straighten completely when at cryogenic temperatures. As the cryogenic fluid no longer flows through the product pipe, the product pipe 1 can be returned to its original shape when the product pipe returns to ambient temperature. It is useful to keep 1) not fully straightened.

Spacers prevent the product pipe from contacting the inner surface of the carrier pipe, thereby preventing thermal short circuits that hinder vacuum insulation, and managing the managed product pipe buckling at a selected wavelength under proper axial compression. Inducing and preventing the product line from completely straightening at low temperatures such that any desired managed buckling or restoration of the shape to the initial shape occurs when the product line temperature returns to ambient temperature. .

The spacers can be made of any suitable material, such as nylon, and can be attached to the product pipe or the carrier pipe for assembly purposes. Preferably, the pipes are assembled by slipping the product pipe with spacers attached in the carrier pipe. The axial spacing of the spacers may be every half of the wavelength, or any other spacing required to achieve the desired shape of the product pipe.

The modified product pipe shape can be achieved by buckling the product pipe into the carrier pipe under axial loading applied from outside during manufacture of the pipeline system, by pre-plastic forming, or by a combination of the two methods. have. The axial compressive force load exerted on the product pipe at ambient temperature is reacted by the corresponding tension in the carrier pipe and is transmitted by the end bulkhead. This axial load is much smaller than would have been applied by the axial heat shrinkage of the product pipe if the product pipe had had a conventional straight shape.

The wavelength of the deformed shape will depend on the inner diameter of the carrier pipe. The product pipe may be provided such that there is sufficient residual strain in the cryogenic shape of the product pipe to allow the product pipe to return to its original shape when the product pipe undergoes repeated thermal cycling between cryogenic and ambient temperature. The product pipe is of sufficient length to accommodate thermal shrinkage of the product pipe with respect to the carrier pipe without being too stressed at cryogenic temperatures.

The wavelength of the sinusoidal shaped product pipe is such that any preload required at room temperature is achieved such that the product pipe is buckle in the carrier pipe and only moderate stresses and / or strains are produced. To keep the pipe within the allowed radius of curvature, the wavelength of the product pipe is also selected.

While enabling materials such as stainless 308 or 9% nickel steel to be used in the production of the product pipe in subsea LNG pipelines, the shape of the product pipe is subject to thermally induced material axial strain when cooled. Rather, to accommodate heat shrinkage through a change in shape.

The carrier pipe 2 is filled with vacuum to provide insulation and is strong enough to further accommodate the external pressure differential of hydrostatic pressure. The carrier pipe 2 may itself be located in an additional pipe. This additional outer pipe can provide additional insulation, act as a backup layer of insulation, and provide a breakage protection layer.

The carrier pipe may not be straight, for example due to the ups and downs of the seabed on which it is to be placed. This non-straight state of the carrier pipe allows for recovery of the buckled shape when the product line returns from cryogenic temperature to ambient conditions in order to achieve the desired initial buckling of the product pipe during ambient temperature manufacturing conditions. To achieve this will affect how much eccentricity is required.

Any sinusoidal “wave property” of the product line may be in a horizontal or vertical plane or at any angle in between. This orientation is preferably chosen to accommodate the straight state of the carrier pipe, which depends on whether it is further out of plane or vertical.

In another embodiment of the present invention, as shown in FIG. 2, the product pipe 1 may have a spiral shape pre-formed at ambient temperature. The fluid delivery system comprises a product pipe 1 which is preformed in the shape of a steep angle spiral which is included in the vacuum in the carrier pipe 2. The spiral product pipe such that the reduction in the running length of the product pipe 1 when the product pipe 1 is cooled to cryogenic temperatures is accommodated by elastic straightening of a product pipe spiral like a conventional spring. (1) may be precompressed as a spring before being fixed to the carrier pipe 2 by end bulkheads 6.

The carrier pipe may have one or more spiral shaped product pipes. The plurality of product pipes may be interleaved as in a multi start thread. 3 shows one shape in which four product pipes 1 are located in the carrier pipe 2. Spacers 11 help prevent each of the product pipes from contacting the inner surface of the carrier pipe and help prevent the pipes from being completely straight at low temperatures. The multi-product pipe system exemplifies the location of four product pipes within the carrier pipe, but any number of suitable pipes may be used.

The spiral product pipe is manufactured by seam welding in a conventional manner but by additionally pulling an offset between and parallel to the mating edges of the plate forming the seam, so that the permanent steep angle of the helix in the product pipe is permanent. Can make

Another method of manufacturing the spiral product pipes in the carrier pipe is a prefabricated bundle from a far end, with a straighter and longer length compared to the carrier pipe, with the spacer rings pre-fixed to the product pipes. Inserting product pipes into the carrier pipe and securing the far end of the product pipe encasted to the carrier pipe with a bulkhead assembly. At the near end of the carrier pipe, at the same time the freeness of each product pipe into a circle having a diameter smaller than the carrier pipe diameter when each product pipe is allowed to rotate about its own axis such that the product pipes are wound to form interleaved spirals. The ends are twisted. Once formed in a spiral configuration, the product pipes may be secured to the near end bulkhead, which prevents the product pipes from unwinding about their local discrete axial centerlines. And the product pipes push the bulkhead toward the mating flange on the carrier pipe in advance to provide additional heat shrinkage capacity before securing the bulkhead to the mating flange on the carrier pipe with adequate insulation. It is compressed. The carrier pipe then reacts to an axial rotational movement in the torsion of the product pipe which causes the pre-axially applied compressive load in tension and the winding to be unwound about the carrier pipe centerline. As the product pipes are filled with LNG, the preloaded axial load will change in tension as the product pipes contract as they compress the carrier pipe. In this way, as the product pipes are compressed into the shape of twisted and interleaved springs, friction forces are expected to accumulate between the spacers and the inside of the carrier pipe. The torque and compression applied at the bulkhead at the near end cause a phenomenon that causes the maximum allowable stresses in the product pipe just behind the bulkhead at the near end, but between the product pipe and the carrier pipe beyond the anchor point. The product pipe and the product until the anchor point without axial relative movement is reached and the other anchor point without circumferential movement of the product pipes with respect to the inside of the carrier pipe beyond another anchor point is reached. These frictional forces are additional so that the relative movement occurring between the carrier pipes reduces the length of the carrier pipes. The occurrence of "locked-up stresses" will temporarily exclude further winding and compression of the product pipes into the springs. However, if the entire LNG pipeline is manufactured over a length of several kilos and is supported on a land roller path that enables the entire length to be pulled into the sea, the roller path may also be It will be possible to rotate about that long axis. The process of rolling the pipe while twisting and compressing the product pipes is such that the friction anchor points form a spiral shape to securely move the full length of the carrier pipe to a far end and the product pipe at an end close to the spiral shape. As will allow them to be guided, they will sequentially "unlock" the friction anchor points. When the LNG pipeline from the lay barge to the seabed is installed while preventing the pipeline from being rolled over, properly designed product pipes are neutrally floated in the casing pipe to rotate the product pipe. The formation of friction anchor points can be alleviated by enabling the carrier pipe to overflow with seawater so as to prevent the formation of any frictional forces as opposed to overcompression. As a result, appropriate facilities will be required to remove and dry the water in the casing pipe.

Although a flow system in which the product pipe has a sinusoidal or spiral shape is particularly illustrated, in order to enable heat shrinkage when the product pipe is cooled to cryogenic temperatures, the length of the product pipe at ambient temperatures is greater than the length of the carrier pipe. Other shapes for long product pipes can be used.

Each end of the carrier pipe and product pipe is fixed to the bulkhead device. 4 and 5 describe in more detail the bulkhead device at the onshore and offshore ends.

4 shows a landside end device for a fluid delivery system. The product pipes (1) located in the carrier pipe (2) end in a bulkhead (6) which forms a sealed and insulated seal with the carrier pipe (2). The flange 3 welded to the carrier pipe 2 is attached to the land end terminal flange 5. This can be done by any conventional attachment means such as nut and bolt arrangement 4. Suitable insulation material 7, 8 is obtained from the carrier pipe 2, the flanges 3, 5, and the bolt 4 from the bulkhead 6 and the product pipe 1, and the product pipe 1. ) It is used to prevent heat flow into the cryogenic fluid inside. The sealed seal is provided for maintaining a vacuum in the hole 9 of the carrier pipe 2. Preferably, the seal is also waterproof to prevent water from entering the carrier pipe. A tapping device 10 into the carrier pipe 2 may be provided to allow access to the aperture 9 to enable the formation of a vacuum in the carrier pipe 2 using an external vacuum pump. have. Alternatively, the tapping device may be provided in the bulkhead. The product pipe 1 is welded to the bulkhead 6 to form a structural and sealed seal. Figure 4 shows only one product pipe in the carrier pipe for clarity, however, multiple product lines ending in the bulkhead may be used. From the bulkhead to the onshore side, fluid such as LNG is transported to onshore storage facilities using conventional devices and maintained at cryogenic temperatures using conventional thermal insulation materials 13.

5 shows one embodiment of the marine end of the system. An additional bulkhead 6 forms an insulated and hermetically sealed seal with the carrier pipe 2 at the marine end of the pipes as described for the land end of the flow line system. Insulating material 16, 12 prevents heat transfer from the carrier pipe 2 to the bulkhead 6 and product pipes 23, 24, 25, 26. The bulkhead 6 may be attached to an insulated cryogenic tanker coupling terminal 14. More offshore from the bulkhead, LNG is maintained at cryogenic temperatures in LNG tankers and unloading gantries using conventional apparatus.

Onshore and offshore ends of the fluid delivery system while LNG is not actually unloaded or loaded through the product pipes, such as the time between multiple product pipes in a single carrier pipe and the arrival of LNG tanker vessels. By the use of valve arrangements in the wind turbines, cryogenic temperatures can be maintained in the vacuum insulated opening of the carrier pipe by continuously circulating LNG into one or more product pipes and back to other product pipes. . An example of a valve arrangement for a carrier pipe comprising four product pipes at the marine end of the LNG pipeline is shown in FIG. 5. By closing the valves 17, 19 and opening the diversion valve 21 to direct the LNG from the product pipe 23 to the product pipe 26, the LNG from the land facility is returned to the product pipe 23. A single flow loop can be formed to discharge flow through and back through the product pipeline 26. A second LNG loop may be formed which exits from the land terminal via product line 24 and returns back through product line 25 with valves 18 and 20 closed and switch valve 22 open. . However, when the tanker arrives, all the product pipes can be used for the quick unloading of the fluid so that the diverting valves 21, 22 and the valves 17, 18, 19, 20 are opened to allow the tanker to return in a short time. have.

When LNG is maintained at the tanker end on the offshore side, similar to the valve arrangement described for the offshore end, fluid flow from one product pipeline at the onshore end of the pipelines to the other product pipeline Flow loops may be formed for circulating LNG out and back through the product pipelines using an array of valves to divert.

6 shows a cross-sectional view of a complete LNG pipeline. Each of the spiral product pipes 1 located in the carrier pipe 2 is supported by spacers such as spacing rings 11 attached thereto at appropriate locations along the length of the product pipe 1. do. The distance between the spacers 11 supports the product lines in the carrier pipe, and prevents thermal shorts across the vacuum insulation between the product pipes and the carrier pipe, The fluid transport system is positioned to facilitate any axial movement of the product pipe within the carrier pipe as LNG is cooled to cryogenic temperatures and undergoes heat shrinkage when LNG is introduced into the product pipes. It will depend on the conditions that become. Concrete weight coatings 15 may be applied to the complete pipeline to provide stability and mechanical protection to the pipeline at the seabed under the flow of ambient seawater. Trenching along all or part of the length of the pipeline may also protect the pipeline assembly.

The completed LNG pipeline may be supported on the bottom of the sea along the slope from the marine side tanker terminal and may be supported in the gradually inclined trench descending from the shore to the sea bottom from the land side terminal. The fluid delivery system may be used to unload fluid from a tanker into a landside terminal or may be used to transport fluid from a land facility to load the fluid into the tanker.

The LNG pipeline can be pulled into place using conventional installation techniques that are built on the lay pants or made entirely onshore to pull the subsea pipeline. Alternatively, the LNG pipeline may be manufactured in parts and then assembled to form a complete line, each being pulled into place.

Although the present invention has been described with reference to the transport of cryogenic fluids, in particular LNG, the system is suitable for transporting other fluids that cause temperature changes in the product pipe.

Claims (11)

Carrier pipes; And At least one internal product flow pipe located within said carrier pipe and insulated from said carrier pipe, The product pipe has a length greater than the length of the carrier pipe and follows a nonlinear path such that the heat shrink of the product pipe due to the temperature change of the product pipe is accommodated by the elastic geometric deformation of the product pipe. Included within the full length of the system for delivering cryogenic fluids. The method of claim 1, And the product pipe is insulated by vacuum over the carrier pipe. The method of claim 2, And wherein said non-linear path is a path that is generally continuous. The method according to any one of claims 1 to 3, And the product pipe has a sinusoidal shape before it is exposed to a change in temperature. The method according to any one of claims 1 to 3, And the product pipe has a spiral shape before it is exposed to a change in temperature. 6. The method according to any one of claims 1 to 5, And two or more product pipes located within the carrier pipe. The method according to any one of claims 1 to 6, And said carrier pipe comprises at least one spacer for supporting said product pipe. The method of claim 7, wherein And the spacers are located approximately every half of the wavelength of the product pipe. The method according to any one of claims 1 to 8, A bulkhead attached to each end of said carrier pipe and said product pipe. The method according to any one of claims 1 to 9, At least one valve for regulating flow through said product pipe. The method according to any one of claims 1 to 10, Further comprising tapping through the carrier pipe to enable a vacuum to be formed in the carrier pipe.

Images