Non-compensated composite installation method for directly buried hot water heating pipelines

Abstract

The present invention relates to a non-compensated composite installation method for directly buried hot water pipelines for heating, comprising: excavating a trench, laying discontinuous structural pipe fittings, a first long straight pipe section and a second long straight pipe section in the trench; performing a first backfilling treatment on the first long straight pipe section; performing a preheating treatment on the first long straight pipe section, and performing a second backfilling treatment on the preheated first long straight pipe section after the elongation of the first long straight pipe section reaches the requirement; after the temperature of the preheated first long straight pipe section drops to the ambient temperature and stabilizes, connecting the discontinuous structural pipe fittings and the first long straight pipe section, and connecting the first long straight pipe section and the second long straight pipe section; performing a third backfilling on the connected overall structure. Under the condition of ensuring the safe and stable operation of the pipeline system, the construction difficulty and project investment are reduced, the comprehensive cost is reduced, and the safety of the operation of the pipe fittings is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of the design and construction of heating pipelines, and particularly relates to a non-compensated composite installation method for directly buried hot water heating pipelines. Background Art

[0002] In recent years, with the continuous increase of the national urbanization rate, the urban central heating, as a municipal infrastructure, has also been greatly developed. The "heating pipe network", as an important part of the urban central heating system, undertakes the task of timely transporting and distributing the heat generated by the heat source to the heat users, and is an important link connecting the heat source and the heat users. At present, the laying methods of urban heating pipe networks are mainly divided into direct burial laying, trench or pipe gallery laying, overhead laying, etc. Among them, direct burial laying has been widely used due to its advantages such as low project cost, short construction period, small excavation cross-section, and small amount of inspection and maintenance.

[0003] The directly buried heating pipe network is divided into compensated laying and non-compensated laying according to whether there is an anchorage section in the long straight pipe section. In compensated laying, due to the existence of compensators, it is often a weak point in the pipe network. Therefore, compensated laying is used less and less, while non-compensated laying has been widely used because it reduces or eliminates the setting of compensators. Non-compensated direct burial laying is further divided into cold installation and preheating installation according to the installation method of heating pipelines.

[0004] Non-compensated cold installation means that the installation processes such as pipe welding and trench backfilling are carried out at the ambient temperature (the calculated installation temperature is the ambient temperature). At the ambient temperature, the pipe is in a zero-stress state; under the operating conditions, due to the large temperature rise, the internal force and stress of the anchorage section and the expansion amount of the transition section are relatively large.

[0005] Non-compensated preheating installation means that the installation processes such as pipe welding and trench backfilling are carried out at a temperature equal to or higher than the preheating temperature. The thermal expansion amount from the ambient temperature to the preheating temperature is released in advance. When the pipe temperature drops to the ambient temperature, the pipe is in a tensile stress state. When the pipe temperature rises above the preheating temperature, the pipe is in a compressive stress state and produces a prestress effect. Under the operating conditions, due to the release of a certain amount of thermal expansion in advance, the internal force and stress of the non-compensated pipe section and the thermal expansion amount of the transition section are greatly reduced.

[0006] The design principle of non-compensated laying of directly buried hot water heating pipe networks is based on the shakedown analysis method. The shakedown analysis method believes that the occurrence of limited plastic deformation in the pipe will not cause damage, and only cyclic plastic deformation will cause damage to the pipe. In the shakedown analysis method, to determine whether the pipe is in a shakedown state, it is not to look at the magnitude of the strain ε1 generated by the first loading, but to look at the strain change ε1 - ε2 generated during cyclic loading and unloading, which should be less than 2ε s . From the stress perspective, the stress change should be controlled within 2σs (σ s (represents the yield limit of steel). Within the range of Δσ j represents the stress change range between the operating condition and the shutdown condition. The strength condition is: Δσ j ≤2σ s = 3[σ]. That is, when the stress change range of the pipe network is less than 2σ s , an anchorage section can be allowed to exist in the pipe network. Compared with the elastic analysis method, the stress change range allowed by the shakedown analysis method has increased greatly, which greatly broadens the application range of the directly buried laying without compensation, simplifies the construction, shortens the construction period, and saves the project cost.

[0007] According to the "Technical Specification for Directly Buried Hot Water Pipelines in Urban Heating" (CJJ / T 81-2013), the main mechanical and stability calculations for directly buried heating pipelines are as follows:

[0008] ① The equivalent stress change range of the straight pipe of the working pipe is calculated according to the following formula

[0009] Δσ j =(1 - ν)σ t +αE(t1 - t2)≤3[σ]

[0010] In the formula:

[0011] Δσ j —The equivalent stress change range of internal pressure and thermal expansion stress, MPa;

[0012] ν—The Poisson's coefficient of steel, taken as 0.3;

[0013] σ t —The circumferential stress caused by the internal pressure of the pipeline, MPa;

[0014] α—The linear expansion coefficient of the steel of the working pipe, m / (m*℃);

[0015] E—The elastic modulus of the steel of the working pipe, MPa;

[0016] t1—The highest temperature of the pipeline working cycle, ℃;

[0017] t2—The lowest temperature of the pipeline working cycle, ℃;

[0018] [σ]—The allowable stress of steel, MPa.

[0019] ② The axial internal force of the directly buried hot water pipeline without compensation

[0020] Na = Aσ = αE(t1 - t0)A×106

[0021] In the formula:

[0022] Na — Axial internal force of the anchorage section, N;

[0023] α — Linear expansion coefficient of the working pipe steel, m / (m*℃);

[0024] E — Elastic modulus of the working pipe steel, MPa;

[0025] t1 — Maximum temperature of the pipeline working cycle, ℃;

[0026] t0 — Calculated installation temperature of the pipeline, ℃;

[0027] A — Cross-sectional area of the working pipe wall;

[0028] ③ Check of local stability of straight pipe section of directly buried hot water pipeline without compensation

[0029]

[0030] Where:

[0031] D o —— Outer diameter of the working pipe (m);

[0032] δ — Nominal wall thickness of the working pipe (m);

[0033] α — Linear expansion coefficient of the steel [m / (m·℃)];

[0034] E — Elastic modulus of the steel (MPa);

[0035] t1 — Maximum temperature of the pipeline working cycle (℃);

[0036] t0 — Calculated installation temperature of the pipeline (℃);

[0037] ν — Poisson's coefficient of the steel, taken as 0.3;

[0038] P d —— Calculated pressure of the pipeline (MPa).

[0039] Based on the above three groups of formulas, the following conclusions can be drawn:

[0040] According to the design principle of the shakedown analysis method, the main failure of the directly buried heat supply network without compensation is fatigue failure. At the same design temperature, the equivalent stress range of the straight pipeline of the working pipe for cold installation and preheating installation without compensation is the same, that is, the fatigue failure is equivalent and has nothing to do with the installation method; compared with cold installation, the designed installation temperature of the preheated installation pipeline is higher than the outdoor ambient temperature, and its stress level is relatively lower under the operating conditions, and the internal force, stress of the pipeline and the thrust of the fixed pier will decrease, so the overall and local stability of the pipeline will be improved.

[0041] In addition, compared with cold installation, preheating installation also has a preheating process, which has a long construction period, long trench opening time, high construction costs and a greater impact on social travel. Specifically, the differences between preheating installation and cold installation are shown in Table 1:

[0042]

[0043] At present, the design and implementation of direct buried hot water pipeline projects for urban heating in China mainly adopts uncompensated direct buried installation. Among them, small-diameter (generally ≤DN1000) heating pipelines usually adopt uncompensated cold installation, and large-diameter (generally >DN1000) heating pipelines mostly adopt uncompensated preheating installation. However, whether it is uncompensated cold installation or preheating installation, the probability of accidents in long straight pipelines of heating pipelines is extremely low. The places where the probability of accidents in heating pipelines is higher are mainly the locations of heating pipeline fittings that adopt uncompensated cold installation, mainly including elbows, tees and reducers. In addition to the reasons for non-standard construction, the main reason for the above accidents is that the peak stress at the pipe fitting location (peak stress refers to the stress generated around the opening of the pipe fitting when the straight pipe section that bears primary stress and secondary stress releases deformation to the discontinuous pipe fittings such as tees, reducers, corners, elbows, etc.) is too high or exceeds the standard. Summary of the invention

[0044] In order to solve all or part of the above problems, the present invention proposes a non-compensated composite installation method for a directly buried hot water pipe for heating. By combining preheating installation and cold installation, the construction difficulty and project investment are reduced while ensuring the safe and stable operation of the pipeline system, and the safety of pipe operation is improved.

[0045] According to a non-compensated composite installation method of a direct-buried hot water pipe for heating, the direct-buried hot water pipe for heating comprises a structural discontinuous pipe fitting, a second long straight pipe section located at each end of the structural discontinuous pipe fitting, and a first long straight pipe section arranged between the structural discontinuous pipe fitting and the second long straight pipe section, wherein the composite installation method comprises:

[0046] Digging a pipe trench, and laying the structural discontinuous pipe, the first long straight pipe section, and the second long straight pipe section in the pipe trench;

[0047] Performing a first backfilling treatment on the first long straight pipe section;

[0048] Preheating the first long straight pipe section, and after the elongation of the first long straight pipe section reaches the requirement, performing a second backfilling treatment on the preheated first long straight pipe section;

[0049] After the temperature of the first long straight pipe section in the preheating treatment drops to the ambient temperature and stabilizes, connect the discontinuous pipe fitting structure and the first long straight pipe section, and connect the first long straight pipe section and the second long straight pipe section;

[0050] Perform the third backfill on the connected overall structure.

[0051] Further, the discontinuous pipe fitting structure is a connecting elbow;

[0052] The connecting of the discontinuous pipe fitting structure and the first long straight pipe section, and the connecting of the first long straight pipe section and the second long straight pipe section are specifically: connect the connecting elbow and the first long straight pipe section using a first connecting pipe, and connect the first long straight pipe section and the second long straight pipe section using a second connecting pipe.

[0053] Further, the discontinuous pipe fitting structure is a tee pipe fitting.

[0054] Further, before the preheating treatment of the first long straight pipe section, the method further includes: first connect any one end of the main pipeline of the tee pipe fitting to the first long straight pipe section through a first connecting pipe.

[0055] Further, the specific operation of the first backfill treatment on the first long straight pipe section is: perform the first backfill treatment on the first long straight pipe sections at both ends of the main pipeline of the tee pipe fitting;

[0056] The specific operation of the preheating treatment on the first long straight pipe section is: perform the preheating treatment on the first long straight pipe sections at both ends of the main pipeline of the tee pipe fitting;

[0057] The connecting of the discontinuous pipe fitting structure and the first long straight pipe section, and the connecting of the first long straight pipe section and the second long straight pipe section are specifically: connect the other end of the main pipeline of the tee pipe fitting and the first long straight pipe section, and connect the first long straight pipe section and the second long straight pipe section using a second connecting pipe.

[0058] Further, before performing the third backfill on the connected overall structure, the method further includes:

[0059] Perform the first backfill treatment on the first long straight pipe section at one end of the branch pipeline of the tee pipe fitting;

[0060] Perform the preheating treatment on the first long straight pipe section at one end of the branch pipeline of the tee pipe fitting, and perform the second backfill treatment on the preheated first long straight pipe section after the elongation of the first long straight pipe section reaches the requirement;

[0061] After the temperature of the first long straight pipe section in the preheating treatment drops to the ambient temperature and stabilizes, connect one end of the branch pipe of the three-way pipe fitting and the first long straight pipe section using the first connecting pipe, and connect the first long straight pipe section and the second long straight pipe section using the second connecting pipe.

[0062] Furthermore, the discontinuous structure pipe fitting is a reducing pipe.

[0063] Furthermore, before the preheating treatment of the first long straight pipe section, the method further includes: connecting any one end of the reducing pipe to the first long straight pipe section through the first connecting pipe first;

[0064] Connecting the discontinuous structure pipe fitting and the first long straight pipe section, and connecting the first long straight pipe section and the second long straight pipe section specifically means: connecting the other end of the reducing pipe and the first long straight pipe section, and connecting the first long straight pipe section and the second long straight pipe section using the second connecting pipe.

[0065] Furthermore, in the first backfilling treatment of the first long straight pipe section, the distance between the highest plane after backfilling and the uppermost end of the first long straight pipe section is greater than or equal to 1 / 4 times the outer diameter of the first long straight pipe section, and the length of the first long straight pipe section is 500 - 900 meters.

[0066] Furthermore, the third backfilling of the connected overall structure specifically is:

[0067] Backfill and compact the overall structure with medium sand, backfill to at least 200 mm higher than the overall structure, and the compaction coefficient during compaction is greater than or equal to 94%;

[0068] Cover backfill soil above the medium sand and compact the backfill soil. The thickness of the backfill soil is greater than or equal to 300 mm, and the compaction coefficient during compaction is greater than or equal to 94%;

[0069] Backfill the original soil above the backfill soil and compact it. The compaction coefficient during compaction is greater than or equal to 94%.

[0070] As can be seen from the above technical solutions, a non-compensated composite installation method for a directly buried hot water heating pipeline provided by the present invention has the following beneficial effects:

[0071] By adopting a composite installation method of preheating installation near the discontinuous structure pipe fitting and cold installation for other pipe fittings, the present invention reduces the construction difficulty and project investment, reduces the comprehensive cost, and improves the safety of the pipe fitting operation while ensuring the safe and stable operation of the pipeline system. BRIEF DESCRIPTION OF THE DRAWINGS

[0072] Figure 1Method flow chart of a non-compensated composite installation method for a directly buried hot water heating pipeline according to an embodiment of the present invention;

[0073] Figure 2 Schematic diagram of the division of each pipe section when the discontinuous structural fitting is a connecting elbow according to an embodiment of the present invention;

[0074] Figure 3 Schematic diagram of the division of each pipe section when the discontinuous structural fitting is a tee fitting according to an embodiment of the present invention;

[0075] Figure 4 Schematic diagram of the division of each pipe section when the discontinuous structural fitting is a reducing pipe according to an embodiment of the present invention;

[0076] Figure 5 Schematic diagram of pipeline backfilling according to an embodiment of the present invention. Detailed implementation manners

[0077] In order to better understand the purpose, structure and function of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings.

[0078] A non-compensated composite installation method for a directly buried hot water heating pipeline, wherein, as Figure 2-4 shown, the directly buried hot water heating pipeline includes a discontinuous structural fitting, a first long straight pipe section 1 and second long straight pipe sections 2 located at each end of the discontinuous structural fitting, the first long straight pipe section 1 is located between the discontinuous structural fitting and the second long straight pipe sections 2, and the first long straight pipe section 1 is connected to the discontinuous structural fitting, and the first long straight pipe section 1 is connected to the second long straight pipe sections 2; specifically, as Figure 1 shown, the composite installation steps are as follows:

[0079] Step 110: Excavate a trench and lay the discontinuous structural fitting, the first long straight pipe section 1 and the second long straight pipe sections 2 in the trench;

[0080] Step 120: Perform a first backfilling treatment on the first long straight pipe section 1;

[0081] Step 130: Perform a preheating treatment on the first long straight pipe section 1, and perform a second backfilling treatment on the preheated first long straight pipe section 1 after the elongation of the first long straight pipe section 1 reaches the requirement;

[0082] Step 140: After the temperature of the preheated first long straight pipe section 1 drops to the ambient temperature and stabilizes, connect the discontinuous structural fitting and the first long straight pipe section 1, and connect the first long straight pipe section 1 and the second long straight pipe sections 2;

[0083] Step 150: Perform a third backfilling on the connected overall structure.

[0084] In this embodiment, the trench for the pipeline is excavated by using the general construction procedure for directly buried hot water pipelines. After the trench is excavated, the discontinuous structure fittings, the first long straight pipe section 1 and the second long straight pipe section 2 are laid in the trench. Among them, both the first long straight pipe section 1 and the second long straight pipe section 2 are welded by existing straight pipe sections. Therefore, after welding, work such as flaw detection, pressure testing, and joint heat preservation is still required; the first backfilling treatment of the first long straight pipe section 1 in step 120 means backfilling the trench with sand, and the distance between the highest plane after backfilling and the uppermost end of the first long straight pipe section 1 is greater than or equal to 1 / 4 times the outer diameter of the first long straight pipe section 1; the preheating treatment in step 130 usually uses electric preheating, and relevant data is recorded according to the requirements of the preheating construction record document during the preheating process; connecting the discontinuous structure fittings and the first long straight pipe section 1 in step 140 specifically means connecting the discontinuous structure fittings and the first long straight pipe section 1 into one body by means of fixed connection such as welding. Connecting the first long straight pipe section 1 and the second long straight pipe section 2 specifically means: connecting the first long straight pipe 1 and the second long straight pipe section 2 into one body by means of fixed connection such as welding.

[0085] Among them, the first long straight pipe section 1 is a preheated installation pipe section, the length of the first long straight pipe section 1 is 500 - 900 meters, and it is not less than the maximum length of the transition section under the corresponding design parameters and burial depth conditions of the pipe diameter; specifically, the first long straight pipe section 1 can be welded by several pipe sections, and the second long straight pipe section 2 is also welded by several pipe sections. Therefore, before construction, flaw detection, pressure testing, and joint heat preservation are also required for the first long straight pipe section 1 and the second long straight pipe section 2.

[0086] In this embodiment, the first long straight pipe section 1 close to the discontinuous structure fittings adopts non-compensated preheating treatment, which reduces the peak stress of the fittings and improves the operation safety of the fittings; in addition, the second long straight pipe section 2 far from the discontinuous structure fittings adopts non-compensated cold installation, which reduces the construction difficulty and project investment and shortens the construction time; through the combined composite installation method of non-compensated preheating installation and non-compensated cold installation, while ensuring the safe and stable operation of the pipeline system, the comprehensive cost of the project is the lowest; the above method of the embodiment of the present invention is particularly applicable to long-distance, large-diameter, high-parameter pipelines, and heating pipe systems with relatively large stress or internal force in the pipeline.

[0087] In a specific embodiment, as Figure 2 shown, the discontinuous structure fitting is a connecting elbow 5;

[0088] Connecting the discontinuous pipe fitting and the first long straight pipe section 1, and connecting the first long straight pipe section 1 and the second long straight pipe section 2 specifically: Using a first connecting pipe 3 to connect the connecting elbow 5 and the first long straight pipe section 1, and using a second connecting pipe 4 to connect the first long straight pipe section 1 and the second long straight pipe section 2.

[0089] Since the discontinuous pipe fitting is a connecting elbow 5, considering the coaxiality between both ends of the connecting elbow 5 and the first long straight pipe section 1, both ends of the connecting elbow 5 and the corresponding first long straight pipe section 1 are respectively connected by a first connecting pipe 3, and the first long straight pipe section 1 and the second long straight pipe section 2 are connected by a second connecting pipe 4. Specifically, both ends of the connecting elbow 5 are respectively connected to the first long straight pipe section 1 through the first connecting pipe 3, and the other end of each first long straight pipe section 1 is respectively connected to the second long straight pipe section 2 through the second connecting pipe 4. During specific construction, the connection between each pipe section can be achieved by welding; since the connecting elbow 5 and the first long straight pipe section 1 are connected by the first connecting pipe 3, and the first long straight pipe section 1 and the second long straight pipe section 2 are connected by the second connecting pipe 4, there should be a space of about 3 meters between the connecting elbow 5 and the first long straight pipe section 1 for installing the first connecting pipe 3, and the specific length of the first connecting pipe 3 is determined according to the actual installation conditions; there should be a space of about 3 meters between the first long straight pipe section 1 and the second long straight pipe section 2 for installing the second connecting pipe 4, and the specific length of the second connecting pipe 4 is determined according to the actual installation conditions.

[0090] In this embodiment, by adopting a composite installation method combining preheating installation and cold installation for the pipe sections at both ends of the connecting elbow 5, while ensuring the safe and stable operation of the pipeline system, the comprehensive cost of the project is the lowest; it overcomes the situation in the prior art where the peak stress at the pipe fitting position at the connecting elbow 5 is relatively high or exceeds the standard, resulting in accidents.

[0091] In a specific embodiment, the discontinuous pipe fitting is a tee fitting 6, as Figure 3 shown, the tee fitting 6 has a main pipeline and a branch pipeline. The main pipeline is Figure 3 the pipeline in the left - right direction in Figure 3 the figure, and the branch pipeline is Figure 3 the pipeline in the up - down direction in the figure. One end of the main pipeline of the tee fitting 6 is connected to the first long straight pipe section 1 through a first connecting pipe 3. The other end of the main pipeline of the tee fitting 6 and the first long straight pipe section 1 can be directly connected by welding, in which case the two parts are pulled together for welding, or can be connected by welding through another first connecting pipe 3. This situation is as

[0092] In this embodiment, by adopting a combined installation method of preheating installation and cold installation for the pipe segments at both ends of the tee fitting 6, the comprehensive cost of the project is the lowest while ensuring the safe and stable operation of the pipeline system; it overcomes the situation in the prior art where the peak stress at the fitting position of the tee fitting 6 is relatively high or exceeds the standard, resulting in accidents.

[0093] In a specific embodiment, since the discontinuous structure fitting is the tee fitting 6 and the tee fitting 6 has a main pipeline and a branch pipeline, before the preheating treatment of the first long straight pipe segment 1 in step 130, the method further includes: connecting any one end of the main pipeline of the tee fitting 6 to the first long straight pipe segment 1 through the first connecting pipe 3 first.

[0094] In a specific embodiment, since the discontinuous structure fitting is the tee fitting 6 and the tee fitting 6 has a main pipeline and a branch pipeline, the first backfilling treatment of the first long straight pipe segment 1 in step 120 is specifically: performing the first backfilling treatment on the first long straight pipe segments 1 at both ends of the main pipeline of the tee fitting 6;

[0095] The preheating treatment of the first long straight pipe segment 1 in step 130 is specifically: performing the preheating treatment on the first long straight pipe segments 1 at both ends of the main pipeline of the tee fitting 6;

[0096] Connecting the discontinuous structure fitting and the first long straight pipe segment 1, and connecting the first long straight pipe segment 1 and the second long straight pipe segment 2 in step 140 is specifically: connecting the other end of the main pipeline of the tee fitting 6 and the first long straight pipe segment 1, and connecting the first long straight pipe segment 1 and the second long straight pipe segment 2 by using the second connecting pipe 4.

[0097] Among them, connecting the other end of the main pipeline of the tee fitting 6 and the first long straight pipe segment 1 specifically has the following two implementation manners as described above: the first is to pull the other end of the main pipeline of the tee fitting 6 and the first long straight pipe segment 1 together for welding, and the second is as Figure 3 shown, welding and connecting the other end of the main pipeline of the tee fitting 6 and the first long straight pipe segment 1 through the first connecting pipe 3. The first connecting method reduces the welding construction process compared with the second connecting method.

[0098] In a specific embodiment, since the tee fitting 6 includes a branch pipeline and the above method is a treatment method for the main pipeline, after the treatment of the main pipeline and before step 150, it further includes the treatment of the branch pipeline. The treatment method of the branch pipeline is specifically as follows:

[0099] Performing the first backfilling treatment on the first long straight pipe segment 1 at one end of the branch pipeline of the tee fitting 6;

[0100] Preheat the first long straight pipe section 1 at one end of the six pipelines of the three-way pipe fitting. After the elongation of the first long straight pipe section 1 reaches the requirement, conduct a second backfilling treatment on the preheated first long straight pipe section 1.

[0101] After the temperature of the preheated first long straight pipe section 1 drops to the ambient temperature and stabilizes, connect one end of the six pipelines of the three-way pipe fitting and the first long straight pipe section 1 using the first connecting pipe 3, and connect the first long straight pipe section 1 and the second long straight pipe section 2 using the second connecting pipe 4.

[0102] In this embodiment, the first backfilling treatment on the first long straight pipe section 1 at one end of the six pipelines of the three-way pipe fitting also uses sand, and the distance between the highest plane after backfilling and the uppermost end of the first long straight pipe section 1 is greater than or equal to 1 / 4 times the outer diameter of the first long straight pipe section 1; the preheating treatment on the first long straight pipe section 1 at one end of the six pipelines of the three-way pipe fitting also uses electric preheating, and relevant data is recorded according to the requirements of the preheating construction record document during the preheating process; in addition, there should be a space of about 3 meters between one end of the six pipelines of the three-way pipe fitting and the first long straight pipe section 1 for installing the first connecting pipe 3, and the specific length of the first connecting pipe 3 is determined according to the actual installation conditions; there should be a space of about 3 meters between the first long straight pipe section 1 at one end of the six pipelines of the three-way pipe fitting and the second long straight pipe section 2 for installing the second connecting pipe 4, and the specific length of the second connecting pipe 4 is determined according to the actual installation conditions.

[0103] In a specific embodiment, the discontinuous structure pipe fitting is a reducing pipe 7. The reducing pipe here means that the inner diameters of the pipelines are not completely equal, that is, the inner diameter at a certain place or a certain section is not equal to the inner diameters of others, such as a tapered pipe section. As Figure 4 shown, one end of the reducing pipe 7 is connected to the first long straight pipe section 1 through a first connecting pipe 3. The other end of the reducing pipe 7 and the first long straight pipe section can also be connected by direct welding or through another first connecting pipe 3. The other end of each first long straight pipe section 1 is respectively connected to the second long straight pipe section 2 through a second connecting pipe 4; among them, the reducing pipe 7 refers to a pipeline whose inner diameter changes, resulting in the inner diameter at a certain place not being equal to the inner diameters of others. During specific construction, the connection between each pipe section can be achieved by welding.

[0104] In this embodiment, by adopting a composite installation method combining preheating installation and cold installation for the pipe sections at both ends of the reducing pipe 7, while ensuring the safe and stable operation of the pipeline system, the comprehensive cost of the project is the lowest; it overcomes the situation in the prior art where the peak stress at the pipe fitting position at the reducing pipe 7 is relatively high or exceeds the standard, resulting in accidents.

[0105] In a specific embodiment, before the preheating treatment of the first long straight pipe section 1 in step 130, the method further includes: connecting any one end of the reducing pipe 7 to the first long straight pipe section 1 through the first connecting pipe 3 first;

[0106] In step 140, connecting the discontinuous structure pipe fitting and the first long straight pipe section 1, and connecting the first long straight pipe section 1 and the second long straight pipe section 2 specifically means: connecting the other end of the reducing pipe 7 and the first long straight pipe section 1, and connecting the first long straight pipe section 1 and the second long straight pipe section 2 by using the second connecting pipe 4. Similarly, according to the foregoing, there are two construction methods for connecting the other end of the reducing pipe and the first long straight pipe: the first is to pull the other end of the reducing pipe 7 and the first long straight pipe section together for welding, and the second is as Figure 4 shown, welding and connecting the two parts of the other end of the reducing pipe and the first long straight pipe section through the first connecting pipe 3. Among them, the first connection method reduces the welding construction process compared with the second connection method.

[0107] In this embodiment, since the discontinuous structure pipe fitting is a reducing pipe 7 with unequal inner diameters, before preheating the first long straight pipe sections 1 at both ends of the reducing pipe 7, one end of the reducing pipe 7 needs to be welded and connected to the corresponding first long straight pipe section 1 through the first connecting pipe 3, and then the operation in step 130 can be performed, that is, preheating the first long straight pipe sections 1 at both ends.

[0108] In a specific embodiment, in the first backfilling treatment of the first long straight pipe section 1, the distance between the highest plane after backfilling and the uppermost end of the first long straight pipe section 1 is greater than or equal to 1 / 4 times the outer diameter of the first long straight pipe section 1.

[0109] In a specific embodiment, the third backfilling of the connected overall structure specifically is:

[0110] As Figure 5 shown, backfill and tamp the overall structure with medium sand. The cross-section of the backfill is around the pipeline. If there are multiple pipelines arranged side by side, the chest position between adjacent two pipelines also needs to be backfilled. The backfill range is at least 200 mm around the pipeline. The compaction coefficient during tamping is greater than or equal to 94%; cover backfill soil above the medium sand. The backfill soil here is powdery backfill soil, and tamp the backfill soil. The thickness of the backfill soil is greater than or equal to 300 mm, and the compaction coefficient during tamping is greater than or equal to 94%; backfill the original soil above the backfill soil and tamp it. The compaction coefficient during tamping is greater than or equal to 94%.

[0111] It should be noted that for the above embodiments of the present invention: all parts of the directly buried hot water pipeline for heating in the above embodiments adopt prefabricated directly buried insulation pipes. The prefabricated directly buried insulation pipe includes a steel pipe, a polyurethane foam plastic insulation layer, and a high-density polyethylene or fiberglass outer casing. The steel pipe, the polyurethane foam plastic insulation layer, and the high-density polyethylene or fiberglass outer casing are tightly combined into one body to form the prefabricated directly buried insulation pipe.

[0112] Among them, the second longest straight pipe section 2 is a cold installation pipe section, which is welded by several pipes (usually with a single fixed length of 12m) at the outdoor ambient temperature. After welding, it is necessary to pass non-destructive testing, pressure testing, and joint insulation qualification before proceeding with subsequent operations.

[0113] It should be noted that unless otherwise specified, the technical terms or scientific terms used in this application should have the ordinary meaning understood by those skilled in the art to which the present invention belongs.

[0114] In the description of this application, it should be understood that the orientation or positional relationship indicated by terms such as "length", "width", "thickness", etc. is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation to the present invention.

[0115] In addition, terms such as "first", "second", etc. are only used for descriptive purposes and cannot be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features.

[0116] In this application, unless otherwise clearly specified and defined, terms such as "installation", "connection", "connection", "fixation", etc. should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or integrated; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the internal communication of two elements or the interaction relationship between two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0117] 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 them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the various embodiments of the present invention, and they should all be covered by the scope of the claims and the description of the present invention. In particular, as long as there is no structural conflict, the various technical features mentioned in each embodiment can be combined in any way. The present invention is not limited to the specific embodiments disclosed in the text, but includes all technical solutions that fall within the scope of the claims.

Claims

1. A non-compensated composite installation method for directly buried hot water pipelines for heating, characterized in that, The directly buried hot water pipeline for heating includes discontinuous structure pipe fittings, second long straight pipe segments at both ends of the discontinuous structure pipe fittings, and first long straight pipe segments arranged between the discontinuous structure pipe fittings and the second long straight pipe segments, wherein the composite installation method includes: Excavate a trench and lay the discontinuous structure pipe fittings, the first long straight pipe segments and the second long straight pipe segments in the trench; Perform a first backfilling treatment on the first long straight pipe segments; Perform a preheating treatment on the first long straight pipe segments, and perform a second backfilling treatment on the preheated first long straight pipe segments after the elongation of the first long straight pipe segments reaches the requirement; After the temperature of the preheated first long straight pipe segments drops to the ambient temperature and stabilizes, connect the discontinuous structure pipe fittings and the first long straight pipe segments, and connect the first long straight pipe segments and the second long straight pipe segments; Perform a third backfilling on the connected overall structure.

2. The non-compensated composite installation method of the directly buried hot water pipeline for heating according to claim 1, characterized in that, The discontinuous structure pipe fittings are connecting elbows; The connecting of the discontinuous structure pipe fittings and the first long straight pipe segments, and the connecting of the first long straight pipe segments and the second long straight pipe segments specifically are: connecting the connecting elbows and the first long straight pipe segments by using first connecting pipes, and connecting the first long straight pipe segments and the second long straight pipe segments by using second connecting pipes.

3. The non-compensated composite installation method of the directly buried hot water pipeline for heating according to claim 1, characterized in that, The discontinuous structure pipe fittings are tee pipe fittings.

4. The non-compensated composite installation method of the directly buried hot water pipeline for heating according to claim 3, characterized in that, Before performing the preheating treatment on the first long straight pipe segments, the method further includes: connecting any one end of the main pipeline of the tee pipe fitting to the first long straight pipe segment through a first connecting pipe first.

5. The non-compensated composite installation method of the directly buried hot water pipeline for heating according to claim 4, characterized in that, The performing of the first backfilling treatment on the first long straight pipe segments specifically is: performing a first backfilling treatment on the first long straight pipe segments at both ends of the main pipeline of the tee pipe fitting; The performing of the preheating treatment on the first long straight pipe segments specifically is: performing a preheating treatment on the first long straight pipe segments at both ends of the main pipeline of the tee pipe fitting; The connecting of the discontinuous structure pipe fittings and the first long straight pipe segments, and the connecting of the first long straight pipe segments and the second long straight pipe segments specifically are: connecting the other end of the main pipeline of the tee pipe fitting and the first long straight pipe segment, and connecting the first long straight pipe segments and the second long straight pipe segments by using second connecting pipes.

6. The non-compensated composite installation method of the directly buried hot water pipeline for heating according to claim 5, characterized in that, Before performing the third backfilling on the connected overall structure, the method further includes: Performing a first backfilling treatment on the first long straight pipe segment at one end of the branch pipeline of the tee pipe fitting; Performing a preheating treatment on the first long straight pipe segment at one end of the branch pipeline of the tee pipe fitting, and performing a second backfilling treatment on the preheated first long straight pipe segment after the elongation of the first long straight pipe segment reaches the requirement; After the temperature of the preheated first long straight pipe segment drops to the ambient temperature and stabilizes, connecting one end of the branch pipeline of the tee pipe fitting and the first long straight pipe segment by using a first connecting pipe, and connecting the first long straight pipe segment and the second long straight pipe segment by using a second connecting pipe.

7. The non-compensated composite installation method of the directly buried hot water pipeline for heating according to claim 1, characterized in that, The discontinuous structure pipe fittings are reducing pipes; 8. The non-compensated composite installation method of the directly buried hot water pipeline for heat supply according to claim 7, characterized in that Before performing the preheating treatment on the first long straight pipe segments, the method further includes: connecting any one end of the reducing pipe to the first long straight pipe segment through a first connecting pipe first; Connecting the structurally discontinuous pipe fitting and the first long straight pipe section, and connecting the first long straight pipe section and the second long straight pipe section specifically include: connecting the other end of the reducing pipe and the first long straight pipe section, and connecting the first long straight pipe section and the second long straight pipe section by using a second connecting pipe.

9. The non-compensated composite installation method of the directly buried hot water pipeline for heating according to claim 1, characterized in that, During the first backfilling treatment of the first long straight pipe section, the distance between the highest plane after backfilling and the uppermost end of the first long straight pipe section is greater than or equal to 1 / 4 times the outer diameter of the first long straight pipe section, and the length of the first long straight pipe section is 500 - 900 meters.

10. The non-compensated composite installation method of the directly buried hot water pipeline for heating according to claim 1, characterized in that, The third backfilling of the connected overall structure specifically includes: Backfilling and tamping the overall structure with medium sand, the backfilling range is at least 200 mm around the pipe, and the compaction coefficient during tamping is greater than or equal to 94%; Covering backfill soil above the medium sand and tamping the backfill soil, the thickness of the backfill soil is greater than or equal to 300 mm, and the compaction coefficient during tamping is greater than or equal to 94%; Backfilling the original soil above the backfill soil and tamping it, and the compaction coefficient during tamping is greater than or equal to 94%.

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