A construction method for double-layer prestressed oil and gas pipeline

Abstract

The present invention relates to a construction method for a double-layer prestressed oil and gas pipeline, comprising: welding a single-section double-layer pipeline group to form a first pipe string, then placing the pipe string in a pipe trench and anchoring one end of the first pipe string; connecting the two ends of a preheating flexible pipe to the free end of a first inner pipe and a heating device respectively, inputting hot air into the first inner pipe to cause the inner pipe to expand and elongate due to heat; backfilling the pipe trench with covering soil; after the first pipe string reaches a predetermined elongation, lifting the second pipe string into the trench and welding the first inner pipe and the second inner pipe of the two pipe strings; connecting the two ends of the preheating flexible pipe to the free end of the second inner pipe of the second pipe string and the heating device respectively, preheating the first pipe string and the second pipe string that have been lowered into the trench; backfilling the pipe trench of the second pipe string with covering soil; confirming whether the elongation of the first pipe string meets the prestressing requirement, and then welding the outer constraint pipe half-tile of the anchor between the first pipe string and the second pipe string; and continuing the preheating construction of subsequent pipe strings until the last pipe string reaches the predetermined elongation.

Description

Technical Field

[0001] The invention relates to a construction method for a double-layer prestressed oil and gas pipeline, belonging to the technical field of prestressed oil and gas pipeline construction. Background Art

[0002] In polar regions and other low-temperature environments, pipelines transporting high-temperature oil and gas are subject to temperature differences between operation and installation, generating significant thermal expansion forces. This thermal expansion can subject the pipeline to high stresses. When the stress exceeds the pipeline's yield stress, the pipeline may experience localized buckling. Furthermore, if the pipeline itself is initially out of straight, this can also lead to overall buckling. Buckling damage to the pipeline can lead to oil and gas leaks and adversely affect the ecological environment. To ensure safe and reliable pipeline operation, these issues must be fully considered during the design and installation of pipelines in high-altitude, cold, and low-temperature regions, and appropriate measures must be taken to mitigate the effects of thermal expansion on the pipeline.

[0003] One effective method is to apply prestress to oil and gas pipelines to mitigate damage caused by high expansion stress. By stretching and preheating the pipeline, the pipe is axially elongated and fixed. After the stretching or preheating stops, the pipeline is prestressed. This prestress offsets thermal expansion forces caused by temperature changes, thereby reducing stress and deformation in the pipeline.

[0004] For long-distance buried pipelines, if there are no effective measures to constrain the pipeline after prestressing is applied, the pipeline will shrink, causing the applied prestress to disappear or decrease, which will seriously affect the safety performance and stability of the pipeline. Summary of the Invention

[0005] In response to the above technical problems, the present invention provides a construction method for a double-layer prestressed oil and gas pipeline. This method can provide sufficient prestress and effectively constrain the double-layer buried pipeline, and can restore the elongation of the retracted pipeline, thereby ensuring that the pipeline prestress meets the design requirements.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] A construction method for a double-layer prestressed oil and gas pipeline, wherein the basic construction unit of the construction method is a single-section double-layer pipeline, including a first inner pipe and a first outer restraining pipe sleeved outside the first inner pipe, including the following steps:

[0008] Step S01: A single-section double-layer pipe assembly is butt-welded to form a first pipe string. The two ends of the first inner pipe are respectively welded with a first inner and outer pipe anchor and a second inner and outer pipe anchor. However, the first inner and outer pipe anchor is not welded with the anchor of the first outer restraining pipe. The outer restraining pipe half-tile is then hoisted into the pipe trench and one end of the first pipe string is anchored.

[0009] Step S02: connecting the two ends of the preheating flexible tube to the free end of the first inner tube and the heating device respectively, starting the heating device, and inputting hot air into the first inner tube according to the set preheating temperature and time, so that the first inner tube expands and elongates due to the heat;

[0010] Step S03: while the inner pipe is preheated in step S02, the trench is backfilled with soil so that the first outer restraining pipe is restrained by the outer soil cover, and a portion of the pipe end is uncovered;

[0011] Step S04: After the first pipe string reaches a predetermined elongation, preheating is stopped, the preheated flexible pipe is removed, the second pipe string is lifted down into the trench, and the first inner pipe and the second inner pipe of the two pipe strings are welded;

[0012] Step S05: connecting the two ends of the preheating flexible pipe to the free end of the second inner pipe of the second pipe string and the heating device respectively, restarting the heating device to preheat the first pipe string and the second pipe string that have been lowered into the pipe trench;

[0013] Step S06: while preheating the inner pipe in step S05, backfill the trench of the second pipe string with covering soil;

[0014] Step S07: measuring and confirming whether the elongation of the first pipe string meets the prestressing requirement. If so, welding the outer restraining pipe half-tile of the anchor between the first pipe string and the second pipe string;

[0015] Step S08: Repeat steps S04 to S07 to continue preheating the subsequent pipe strings until the last pipe string reaches a predetermined elongation;

[0016] Step S09: Fix the free end of the last pipe string with an anchor flange.

[0017] In the construction method of the double-layer prestressed oil and gas pipeline, preferably, in steps S02 and S05, while preheating the pipe string that has been lowered into the pipe trench, another heating device can be used to preheat the subsequent pipe string to increase the temperature of the pipe string and reduce the subsequent preheating time in the pipe trench.

[0018] In the construction method of the double-layer prestressed oil and gas pipeline, preferably, in steps S03 and S06, after the trench is backfilled with soil, compaction equipment can be used to apply pressure to the soil to increase the density of the soil and the restraint force of the soil on the pipeline.

[0019] The present invention has the following advantages due to the adoption of the above technical solution:

[0020] 1. The present invention uses hot air through a heating device to provide heat source input to the inner steel pipe of a double-layer oil and gas pipeline. After the inner steel pipe expands to a predetermined elongation, preheating is stopped, the inner steel pipe of the next section of the pipe string is connected and preheating is resumed. The pipe trench is backfilled and covered with soil. Then, the inner steel pipe is connected to the outer restraining steel pipe through an anchor, and the retraction of the pipe string is restrained by the interaction between the outer pipe and the soil.

[0021] 2. The present invention can effectively limit the cooling and shrinkage of the preheated pipe string through the interaction between the external constraint pipe of the subsequent pipe string and the covering soil, avoiding the problem that after the pipe string shrinks beyond the virtual anchor point of the pipe end, the soil strength gradually increases, requiring a significant increase in the preheating temperature to be restored, or the inability to re-extend to the predetermined value.

[0022] 3. The pipe string preheating and preheating recovery process of the present invention only need to overcome the friction between the inner steel pipe and the outer constraint pipe, and are not affected by the covering soil. Therefore, there is no need for an excessively high preheating temperature and a good preheating elongation effect can be guaranteed. During the pipe string preheating process, the pipe trench can be backfilled simultaneously, which significantly saves construction time. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 A flow chart of a double-layer prestressed oil and gas pipeline construction method provided by one embodiment of the present invention;

[0024] Figure 2 for Figure 1 The layout diagram of steps S02 and S03, i.e., the schematic diagram of the first pipe string preheating and backfilling steps;

[0025] Figure 3 for Figure 1 The layout diagram of step S04, i.e., stopping preheating and connecting the first pipe string and the second pipe string;

[0026] Figure 4 for Figure 1 The layout diagram of steps S05 and S06, i.e., the schematic diagram of resuming preheating and backfilling the trench;

[0027] Figure 5 for Figure 1 The layout diagram of step S07, i.e., the schematic diagram of the outer tube half-tile of the anchor between the front and rear tube strings;

[0028] The marks in the figure are as follows:

[0029] 1-first inner tube; 2-first outer restraint tube; 3-first inner and outer tube anchor; 4-second inner and outer tube anchor; 5-first pipe string; 6-heating equipment; 7-preheating flexible tube; 8-trench covering; 9-anchor outer restraint tube half tile; 10-second pipe string; 11-second inner tube; 12-second outer restraint tube; 13-third inner and outer tube anchor. DETAILED DESCRIPTION

[0030] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions of the present invention are described clearly and completely below. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. All other embodiments derived by ordinary persons in this field based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0031] Unless otherwise defined, the technical or scientific terms used in the present invention shall have the usual meanings understood by persons of ordinary skill in the field to which the present invention belongs. The words "first", "second", "third", "fourth" and similar terms used in the present invention do not indicate any order, quantity or importance, but are only used to distinguish different components. Words such as "include" or "comprise" mean that the elements or objects preceding the word include the elements or objects listed after the word and their equivalents, without excluding other elements or objects. Words such as "connect" or "connected" are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect.

[0032] For ease of description, spatially relative terms may be used herein to describe the relationship of one element or feature relative to another element or feature as shown in the figures, such as "inside," "outside," "inner side," "outer side," "lower," "upper," etc. Such spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures.

[0033] In polar regions and other low-temperature environments, pipelines transporting high-temperature oil and gas are subject to temperature differences between operation and installation, generating significant thermal expansion forces. This thermal expansion can subject the pipeline to high stresses. When the stress exceeds the pipeline's yield stress, the pipeline may experience localized buckling. Furthermore, if the pipeline itself is initially out of straight, this can also lead to overall buckling. Buckling damage to the pipeline can lead to oil and gas leaks and adversely affect the ecological environment. To ensure safe and reliable pipeline operation, these issues must be fully considered during the design and installation of pipelines in high-altitude, cold, and low-temperature regions, and appropriate measures must be taken to mitigate the effects of thermal expansion on the pipeline.

[0034] To address the above technical issues, the present invention provides a double-layer prestressed oil and gas pipeline construction method. This method can provide sufficient prestress and effectively constrain the double-layer buried pipeline, and can also restore the elongation of the retracted pipeline, thereby ensuring that the pipeline prestress meets the design requirements. The technical solution of the present invention is described in detail below with reference to specific examples.

[0035] like Figure 1As shown, the present invention relates to a double-layer prestressed oil and gas pipeline construction method, the basic construction unit of which is a single-section double-layer pipeline, a pipe string consisting of an inner pipe, an outer constraint pipe and an anchor, and the construction equipment includes: a heating device 6, a preheating flexible pipe 7 and a trench covering 8.

[0036] In a preferred embodiment of the present invention, a thermal insulation layer can be set between the inner tube and the outer constraint tube according to the oil and gas transportation flow assurance requirements, but it does not affect the implementation process of the present invention. The inner tube and the outer constraint tube are both carbon steel pipes.

[0037] The construction method involved in the present invention has the following specific process:

[0038] Step S01: First, a double-layer pipe assembly with a single length of 18 meters is welded to form a first pipe string 5 with a length of 1 km. The first inner pipe 1 is welded to its two ends with a first inner and outer pipe anchor 3 and a second inner and outer pipe anchor 4, respectively. However, the outer anchoring pipe half-piece 9 is not welded to the first inner and outer pipe anchor 3. The first pipe string 5 is then lifted and placed into the trench, and one end of the second inner and outer pipe anchor 4 is secured. The length of the first pipe string 5 should be determined based on the project's specific terrain conditions, available construction time constraints, and other factors.

[0039] Step S02: Connect the ends of the preheating flexible tube 7 to the free end of the first inner tube 1 and the heating device 6 (specifically, an air heater), respectively. The heating device 6 is activated, supplying hot air to the first inner tube 1 according to the set preheating temperature and time, causing the first inner tube 1 to expand and elongate due to the heat. The required thermal expansion and elongation of the first inner tube 1 is calculated as ∆L = L1 × α × (T2 - T1), where L1 is the initial length of the first tube string 5; α is the thermal expansion coefficient of the steel; T1 is the pre-preheating pipe temperature; and T2 is the average post-preheating pipe temperature, which is the initial pipe temperature used for pipe stress calculation. Because friction between the first inner tube 1 and the first outer restraining tube 2 must be overcome, the output temperature of the heating device 6 must be higher than temperature T2.

[0040] Step S03: Figure 2 As shown, while preheating the first inner tube 1 in step S02, the trench is backfilled with covering soil 8, subjecting the first outer constraint tube 2 to the external soil cover constraint. Partial areas of the tube ends remain uncovered. The depth of the soil cover is determined based on factors such as the depth of permafrost, the impact of temperature on vegetation, and the overall buckling requirements of the pipeline. In this embodiment, the soil cover depth is 2.2 m. The area of ​​the first pipe string 5 where the ends are not backfilled is primarily used for later pipe string docking and anchor welding, as well as for placing preheat elongation markers to facilitate checking the effectiveness of preheating. This area can be backfilled after all pipelines are preheated and the pipe ends are anchored.

[0041] Step S04: Figure 3As shown, when the first tube string 5 reaches the predetermined elongation ∆L, the heating device 6 stops preheating. Then, the preheated flexible tube 7 is removed, the second tube string 10 is lifted down into the trench, and the first inner tube 1 and second inner tube 11 of the two tube strings are welded. During this step, the temperature of the first inner tube 1 of the first tube string 5 decreases to a certain extent and shrinks.

[0042] Steps S05 and S06: Figure 4 As shown, the ends of the preheating flexible pipe 7 are connected to the free ends of the second inner tube 11 of the second pipe string 10 and the heating device 6, respectively. The heating device 6 is then restarted to preheat the first pipe string 5 and the second pipe string 10, which have already been lowered into the trench. In the previous step S04, due to the cessation of heating by the heating device 6, the first inner tube 1 of the first pipe string 5 will cool down, causing the steel pipe temperature to fall below the required preheating temperature and the elongation to fall below the required elongation ∆L. By restarting the preheating device 6, the temperature of the first pipe string 5 is restored to above the required temperature T2, as determined by the return to the predetermined elongation position. During this process, the second pipe string 10 can be backfilled with cover soil 8.

[0043] After measuring and confirming that the elongation of the first pipe string 5 has met the prestressing requirement, step S07 is executed, that is, welding the anchor outer constraint pipe half-tile 9 between the first pipe string 5 and the second pipe string 10, as shown in FIG. Figure 5 This step combines the first and second pipe strings 5, 10 into a single unit. Assuming the second pipe string 10 is sufficiently long and the restraining effect of the covering soil 8 is greater than the cooling and retraction force of the pipe string, the first pipe string 5 will remain locked and will not retract. If the second pipe string 10 is insufficient, further pipe strings can be added to overcome the cooling and retraction force, locking the first pipe string 5.

[0044] At this point, the prestressing construction of the first pipe string 5 is completed. The above steps can be repeated to carry out the preheating construction of subsequent pipe strings until the last pipe string reaches the predetermined elongation and the free end of the last pipe string is fixed with an anchor flange.

[0045] The present invention uses hot air to provide heat source input to the inner pipe of the double-layer oil and gas pipeline through the heating device 6. After the inner pipe expands to a predetermined elongation, preheating is stopped, the inner pipe of the next section of the pipe string is connected but the anchor is not welded to the outer constraint pipe half tile of the anchor, preheating is resumed, the pipe trench is backfilled and covered with soil, and then the inner pipe and the outer constraint pipe are connected through the anchor, relying on the interaction between the outer pipe and the soil to constrain the retraction of the pipe string.

[0046] During construction, adjacent pipe strings are connected and load-transmitted via anchors. If the preceding pipe string has not yet reached its intended elongation, the anchor half-piece is not welded. This allows the preceding pipe string to extend only against internal and external friction, without having to resist the interaction between the outer pipe and the soil. Once the preceding pipe string reaches its intended elongation, the outer constraint pipe half-piece of the anchor can be welded between the pipe strings. This utilizes the interaction between the subsequent pipe string and the soil to constrain the cooling and retraction of the preceding pipe string.

[0047] The present invention can effectively limit the cooling and shrinkage of the preheated preceding pipe string through the interaction between the outer constraint pipe of the subsequent pipe string and the covering soil, thereby avoiding the problem that after the pipe string shrinks beyond the virtual anchor point of the pipe end, the soil strength gradually increases and a substantial increase in the recovery preheating temperature is required or the preheating cannot be re-extended to the predetermined value; during the pipe string preheating and preheating recovery process, only the friction between the inner steel pipe and the outer constraint pipe needs to be overcome, and it is not affected by the covering soil. Therefore, an excessively high preheating temperature is not required and a good preheating and elongation effect can be guaranteed; and during the pipe string preheating process, the pipe trench can be backfilled simultaneously, which significantly saves construction time.

[0048] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A construction method for a double-layer prestressed oil and gas pipeline, wherein the basic construction unit of the construction method is a single-section double-layer pipeline, comprising a first inner pipe (1) and a first outer restraining pipe (2) sleeved outside the first inner pipe (1), characterized in that: The steps include: Step S01: a single-section double-layer pipe group is welded to form a first pipe string (5), and the two pipe ends of the first inner pipe (1) are respectively welded with a first inner and outer pipe anchor (3) and a second inner and outer pipe anchor (4), but the first inner and outer pipe anchor (3) is not welded with the anchor outer constraint pipe half tile (9) of the first outer constraint pipe (2), and then the first pipe string (5) is lifted and placed into the pipe trench and one end of the first pipe string is anchored; Step S02: connecting the two ends of the preheating flexible tube (7) to the free end of the first inner tube (1) and the heating device (6), respectively, starting the heating device (6), and inputting hot air into the first inner tube (1) according to the set preheating temperature and time, so that the first inner tube (1) expands and elongates due to the heat; Step S03: while the inner pipe is preheated in step S02, the pipe trench is backfilled with covering soil (8), so that the first outer constraint pipe (2) is subject to external soil covering constraint, and a portion of the pipe end area is not covered; Step S04: After the first pipe string (5) reaches a predetermined elongation, preheating is stopped, the preheating flexible pipe (7) is removed, the second pipe string (10) is lifted down into the ditch, and the first inner pipe (1) and the second inner pipe (11) of the two pipe strings are welded; Step S05: connecting the two ends of the preheating flexible pipe (7) to the free ends of the second inner pipe (11) of the second pipe string (10) and the heating device (6), restarting the heating device (6), and preheating the first pipe string (5) and the second pipe string (10) that have been lowered into the pipe trench; Step S06: while preheating the inner pipe in step S05, backfill the trench of the second pipe string (10) with covering soil (8); Step S07: measuring and confirming whether the elongation of the first pipe string (5) has met the prestressing requirement, and if so, welding the anchor member outer restraint pipe half-tile (9) between the first pipe string (5) and the second pipe string (10); Step S08: Repeat steps S04 to S07 to continue preheating the subsequent pipe strings until the last pipe string reaches a predetermined elongation; Step S09: Fix the free end of the last pipe string with an anchor flange.

2. The construction method of a double-layer prestressed oil and gas pipeline according to claim 1, characterized in that: In steps S02 and S05, while preheating the pipe string that has been lowered into the pipe trench, another heating device (6) is used to preheat the subsequent pipe string to increase the temperature of the pipe string and reduce the subsequent preheating time in the pipe trench.

3. The construction method of a double-layer prestressed oil and gas pipeline according to claim 1, characterized in that: In steps S03 and S06, after the trench is backfilled with soil, compaction equipment is used to apply pressure to the soil to increase the density of the soil and the restraint force of the soil on the pipeline.

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