Water pressure test method of PCCP pipeline without backwall in mountainous conditions

Abstract

The present application relates to the technical field of pipeline hydrostatic test, and particularly relates to a PCCP pipeline hydrostatic test method without backwall design under mountain conditions. The test method comprises the following steps: S1, selecting a test pipe section as a hydrostatic test section, and connecting one end of the hydrostatic test section with a PCCP pipe socket; S2, calculating and designing a plug of the test pipe section according to a plug stress thickness calculation formula, and plugging the other end of the hydrostatic test section with the plug; S3, taking the test pipe section and the surrounding soil after backfilling as a natural backwall, and checking whether the bearing capacity of the two soils meets the backwall requirement; S4, installing test equipment on the test pipe section to build a test system; S5, injecting water into the test pipe section, exhausting, and increasing pressure test, and judging whether the pipeline installation quality is qualified through pressure drop or water seepage. The method uses the natural backwall formed by the undulating terrain and the steel bend pipe to perform hydrostatic test, without backwall construction, thereby saving a lot of construction period and reducing construction cost.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of pipeline hydrostatic test, in particular to a PCCP pipeline hydrostatic test method without back wall design under mountain conditions. BACKGROUND

[0002] Long-distance water conveying pipeline projects have the advantages of high water utilization rate, good water quality guarantee, and small land occupation, and are the main engineering form to solve the water supply and demand contradiction in water shortage areas. In the long-term development process, the following characteristics gradually appear: (1) The pipeline conveying line is getting longer and longer, and the requirements for engineering regulation and preservation measures and auxiliary valve configuration are getting higher and higher; (2) The pipeline working pressure is getting higher and higher, and the pipeline pressure has developed from low pressure 0.1MPa to 3.0Mpa or even higher; (3) The pipeline diameter is generally increased. For long-distance high-pressure water conveying pipelines, hydrostatic test as the last quality guarantee process before the project is put into operation, its technical requirements and construction difficulty are also increasing.

[0003] The hydrostatic test has problems of high cost, long construction period, and low success rate, and the main pain points are as follows: first, due to the increase of pipeline pressure and diameter, the reaction force provided by the back wall system needs to be greatly increased, which puts higher requirements on the design and construction of the back wall; second, the existing hydrostatic test mostly uses cast-in-place concrete as the back wall, and the back wall pouring, maintenance and removal have a huge impact on the construction period and cost.

[0004] In addition, in the existing pipeline laying process, when the PCCP pipeline passes through the mountain area, due to geological reasons, it is impossible to lay a straight pipe, and a steel bend pipe needs to be used for crossing, but when the steel bend pipe crossing pipeline is subjected to pipeline hydrostatic test, not only is it difficult to establish a back wall, but also there is no effective pipeline hydrostatic test method. Therefore, it is urgent to solve.

[0005] The above content is only used to assist in understanding the technical solutions of the present application, and does not represent the acknowledgement of the above content as the closest prior art. SUMMARY

[0006] The technical problem to be solved by the present application is to provide a PCCP pipeline hydrostatic test method without back wall design under mountain conditions, which uses the undulating terrain and the steel bend pipe to form a natural back wall for hydrostatic test, without back wall construction, saving a lot of construction period and reducing construction cost.

[0007] To achieve the purpose, the technical scheme of the present application is as follows: the PCCP pipeline hydrostatic test method without back wall design under mountain conditions comprises the following steps:

[0008] S1, selecting a test pipe section as a hydrostatic test section, and connecting one end of the hydrostatic test section with a PCCP pipe socket;

[0009] S2, the plug of the test pipe section is calculated and designed according to the plug stress thickness calculation formula, and the other end of the hydrostatic test section is sealed with the plug;

[0010] S3, the test pipe section and the surrounding soil after backfilling are used as a natural back wall, and the bearing capacity of the two soils is calculated by the allowable resistance formula of the back soil, the stress width formula of the back soil and the length formula of the back soil layer to determine whether the bearing capacity of the two soils meets the requirement of the back wall;

[0011] S4, after determining that the bearing capacity of the two soils meets the requirement of the back wall, the test equipment is installed in the test pipe section to construct a test system;

[0012] S5, then water is injected into the test pipe section, air is exhausted, and the test is carried out under pressure, and whether the pipeline installation quality is qualified is determined by pressure drop or water seepage.

[0013] Preferably, the test pipe section is selected as the elbow where the terrain rises more than 11.25° in the vertical direction as the two ends of the test pipe section.

[0014] Preferably, the plug stress thickness calculation formula in step S2 is:

[0015]

[0016] In the formula: is the stress thickness, mm; P is the design pressure of the plug, MPa; is the nominal diameter, mm; is the allowable stress of the steel plate at the design temperature, MPa; and Ф is the weld coefficient, which is 0.85.

[0017] Preferably, the allowable resistance formula of the back soil in step S3 is:

[0018]

[0019] In the formula: is the passive earth pressure per 1m width, kN / m; is the gravity density of the back soil, kN / m3; c is the cohesion of the back soil, kN / m2; H is the height of the back wall, which can be equivalent to the height difference of the pipeline, m; h is the height from the top of the back wall to the ground, which can be equivalent to the height from the top of the highest pipe to the ground, m; Kp is the passive earth pressure coefficient, 2 is the internal friction angle of the back soil, which is 16°, and the calculation result is =1.76.

[0020] Preferably, the stress width formula of the back soil in step S3 is:

[0021] B≥2.0

[0022] B is the width of the back soil body under force, m; is the force transmitted to the back by the pipe block, the size is equal to the total thrust F of the water pressure test, kN; 2.0 is a safety factor.

[0023] Preferably, the length of the back soil layer in step S3 is:

[0024]

[0025] L is the length in the force direction of the back, m; is an additional safety length, 0.5 m.

[0026] The beneficial effects of the present application are embodied in:

[0027] The method provided by the present application firstly proposes that the characteristics of the steel bend pipe crossing in the mountainous conditions along the PCCP pipeline are used, and the water pressure test is carried out by fully utilizing the natural back wall formed by the undulating terrain and the steel bend pipe. Compared with the traditional water pressure test of setting the back wall, the method can avoid the production and removal of the back wall, shorten the construction period required for the production of the back wall, reduce the labor and material costs, improve the success rate of the test, improve the safety during the test, and has good environmental protection effect by reducing the use of concrete and other back wall production materials. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 is the flow chart of the method of the present application;

[0029] Figure 2 is the terrain and pipeline schematic diagram at A0+054 in the implementation of the present application;

[0030] Figure 3 is the terrain and pipeline schematic diagram at Y5+740 in the implementation of the present application. DETAILED DESCRIPTION

[0031] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, not all the embodiments. The embodiments in the present application and the features in the embodiments can be combined with each other without conflict. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0032] EMBODIMENT

[0033] As Figure 1 ​​As shown, by the method provided by the application, taking the implemented Anning City Chemu River water pipeline construction project (phase III) one bid section as an example

[0034] The implementation process is as follows:

[0035] Test pipe section selection: as shown in the figure Figures 2-3 As shown, the principle is to select a large terrain fluctuation as the two ends of the test pipe section, select A0+054 as the end, and Y5+740 as the other end, and the length of this section is 5794m, and this section is used as the water pressure test section.

[0036] Carry out test system calculation:

[0037] Plug design calculation:

[0038] The plug is welded, the plug is provided with a water inlet / outlet and an exhaust port, and is provided with a socket or a spigot. The plug is designed and calculated according to the following method.

[0039] The stress thickness calculation formula of the plug plate is:

[0040]

[0041] In the formula: The stress thickness is mm; P is the design pressure of the plug plate, 1.3MPa; The nominal diameter is 1400mm; The allowable stress of the steel plate at the design temperature is 133MPa; and the welding coefficient is 0.85.

[0042] The calculation result is =8.1mm, in order to ensure the safety of the pressure test, the thickness of the plug plate used in the project is 12mm.

[0043] Natural back wall system checking

[0044] The method provided by the application takes a pipe section of the Anning City Chemu River reservoir water pipeline construction project (phase III) as an example for calculation, the pipe material of the pipe section is PCCP pipe, the pipe diameter D=1400mm, the pipe working pressure P=1.0Mpa, the test pressure =P+0.3Mpa=1.3Mpa, the total thrust of the water pressure test (the force acting on the back wall) =2000kN.

[0045] A0+054 to A0+094 is a steel pipe section, and is connected with the PCCP pipe at the A0+094 position, so the steel pipe section from A0+054 to A0+094 and the surrounding soil after backfilling can be regarded as a natural back wall, and similarly, the steel pipe section from Y5+667 to Y5+740 and the surrounding soil after backfilling can be regarded as a natural back wall, and the bearing capacity of the two soil bodies needs to be checked.

[0046] The allowable resistance of the back soil: When the resultant force of the force transmitted to the back soil by the pipe plug coincides with the passive earth pressure on the back soil, the allowable resistance of the back soil can be calculated by the following formula:

[0047]

[0048] In the formula: --Passive earth pressure per 1m width, kN / m; --The density of the backing soil, taken as 20.0 kN / m³; c--The cohesion of the backing soil, taken as 30 kN / m²; H--The height of the back wall, which can be equivalent to the pipe height difference, taken as 5.5 m at A0+054 and 14.3 m at Y5+740; h--The height from the top of the back wall to the ground, which can be equivalent to the height from the top of the highest pipe to the ground, taken as 0.6 m at A0+054 and 2 m at Y5+740; Kp--Passive earth pressure coefficient. 2 (θ is the internal friction angle of the back soil, taken as 16°), the calculation yields... =1.76.

[0049] The calculation yields position A0+054. =1086.35kN / m, at Y5+740 =5744kN / m.

[0050] Formula for calculating the stress-bearing width of the back soil:

[0051] B≥2.0 /

[0052] In the formula: B is the width of the back soil under stress, in meters; The force transmitted from the pipe plug to the back is equal to the total thrust F of the water pressure test, in kN; 2.0 is the safety factor.

[0053] The calculations show that B ≥ 3.7m at A0+054 and B ≥ 0.7m at Y5+740, which clearly indicates that the width of the back soil at both locations meets the requirements.

[0054] Formula for calculating the length of the back soil layer:

[0055] ,

[0056] In the formula: L is the length along the direction of the force applied to the back, in meters; To add a safety margin, we take 0.5m. Calculations show that L = 23.7m at A0+054 and L = 54m at Y5+740, which clearly meets the length requirements.

[0057] Under the condition of mountainous terrain, the working condition that can be checked by the above water pressure test natural back wall system is very common, so this method has universality. If this method is used, it can save a lot of manpower and material resources needed to make the back wall system during the conventional water pressure test, and the artificially made back wall system is also an unstable factor and a weak link in the entire water pressure test process. The reason for a large number of water pressure test failures is that the back wall system is not firm enough to cause the plug to fall off and fail to stabilize pressure. Using this method perfectly avoids this risk and solves the problem of the difficulty of constructing a firm artificial back wall system, thereby greatly improving the success rate of water pressure test.

[0058] Test system installation

[0059] Instrument and valve installation: one DN25 exhaust hole is arranged at a high position of the upstream plug, a exhaust tee is installed, one DN15 pressure gauge is installed on the side, one DN80 water injection hole is arranged, and one ball valve is arranged on each pipeline. A small ball valve is installed in front of the pressure gauge.

[0060] The downstream plug exhaust hole and pressure gauge are arranged in the same way as the upstream. A DN80 drain hole (also used as a water injection hole) is arranged at the bottom of the downstream pipeline, a tee is installed, and a DN40 pressurizing hole is arranged on the side to connect the electric test pump. One ball valve is installed on each pipeline.

[0061] Selection and installation of pressurizing equipment and pressure gauges: the pressure gauge is composed of a main gauge and a verification gauge, which are installed at both ends of the test pipe section and connected by a pressure gauge buffer pipe. The pressure gauge has a range of 0-2.5Mpa and an accuracy of 0.25, considering the test pressure of the pressure test section. The nominal diameter of the gauge shell is not less than 150mm for easy reading. The pressure gauge is calibrated before use. When connecting the pressure gauge, the air in the branch pipe is exhausted to prevent the pressure gauge pointer from frequently fluctuating and damaging the pressure gauge during pressure rise. According to the pressure of the pressure test section, the D12-25X10 horizontal multi-stage centrifugal pump with a lift of not less than 200m is selected.

[0062] Test process

[0063] Water injection: water injection is divided into two stages. First, pressureless water injection is performed using two water injection pumps to inject water from the two reserved water injection holes. The water injection speed should be as slow as possible to ensure that all air in the pipeline is exhausted to prevent air hammer or water hammer effect in the pipeline. When the downstream water injection port cannot inject water, close the low point water injection port until the upstream water injection port cannot inject water. Then, pressure water injection is performed using a pressurizing pump to gradually pressurize and inject water. The pipeline is filled with water by using the method of pressurizing, injecting water, and exhausting air. The pressurizing pressure should not be higher than the working pressure when the pipeline is filled with water.

[0064] Air exhaust: open the air exhaust valves at the upstream and downstream during the water injection process. Close the air exhaust valves after the pressure water injection is completed.

[0065] Pipe soaking: After the test pipe section is filled with water, it should be soaked for 72 hours according to the specification requirements. After soaking, the lost water in the compensation pipe section is replenished, and the connection of each equipment and the part of the pipe section to be tested are checked for water leakage. If there is no hidden danger in each check, the test is carried out.

[0066] Step-by-step pressure increase: After the preparation work and other matters are normal, the pressure is increased. The pressure increase is carried out by an electric pressure test pump. The pressure increase should be slow and smooth, generally in 3-5 times to the test pressure.

[0067] Pre-test: First, slowly increase the pressure to 1.9 MPa of the test pressure and stabilize for 30 minutes. If the pressure drops during this period, water can be added to increase the pressure, but it should not exceed the test pressure. Check the pipe interface, fittings, etc. for water leakage and damage. If there is water leakage or damage, stop the pressure test immediately, identify the cause and take appropriate measures before retesting.

[0068] Main test: Stop water replenishment and stabilize for 15 minutes. When the pressure drops by no more than 0.03 MPa after 15 minutes, reduce the test pressure to the working pressure of 1.0 MPa and maintain constant pressure for 30 minutes.

[0069] During the pressure increase of the pipeline, the gas in the pipeline should be removed. If the spring pressure gauge needle swings and is unstable during the pressure increase process, and the pressure increase is slow, the pipeline should be re-vented before the pressure is increased again. The pressure should be increased in stages. After each increase, check the back, support, pipe body and interface for abnormal phenomena before continuing to increase the pressure. During the water pressure test, the back support and both ends of the pipeline must not be occupied. During the water pressure test, defects must not be repaired. If defects are found, they should be marked and repaired after the pressure is released.

[0070] Test result determination: According to the "Water Supply and Drainage Pipeline Engineering Construction and Acceptance Specification" (GB 50268-2008), one or both of the allowable pressure drop value and the allowable water leakage value can be selected as the final determination basis for test qualification.

[0071] Pressure drop value and water leakage value determination: When the pressure reaches the test pressure, stabilize for 15 minutes. If there is no pressure drop after 15 minutes, reduce the pressure value to the design working pressure and maintain constant pressure for 30 minutes. Check the pressure value rise and fall and the appearance of the test pipe section, such as:

[0072] (1) If the PCCP pipeline pressure drop is less than 0.03 MPa and there is no leakage, it is determined to be qualified.

[0073] (2) If the spiral welded steel pipe has no pressure drop and no water leakage, it is determined to be qualified.

[0074] Allowable water leakage determination: When the pressure pipeline uses the allowable water leakage as the final qualification basis,

[0075] (1) The measured water leakage of PCCP pipeline shall be less than or equal to: 0.14 ≈ 5.238 (L / min·km);

[0076] (2) The measured water leakage of spiral welded steel pipe pipeline shall be less than or equal to: 0.05 1400 ≈1.871 (L / min·km);

[0077] Graduated pressure relief and drainage: after the test is completed, the pipeline is slowly depressurized through the drain, and the depressurization speed is controlled to be not greater than 0.1 MPa / min. After the depressurization is completed, the test water is discharged into the specified drainage area by using the water pump. During the drainage process, the exhaust valve on the pressure test pipeline is opened to discharge water and reduce pressure, so as to prevent the pipeline from being vacuumized.

[0078] The method provided by the present application is compared with the cost, construction period and success rate of the traditional back wall system, as shown in the following table:

[0079] Comparison table of cost, construction period and success rate of traditional back wall system

[0080]

[0081] From the above table, it can be seen that the method provided by the present application not only can save the construction period, but also can reduce the test cost and improve the test success rate, and has strong application and promotion prospect.

[0082] The above description is only the preferred embodiment of the present application, and is not used to limit the present application, and any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for hydrostatic testing of PCCP pipelines without back walls in mountainous conditions, wherein the PCCP pipeline traverses mountainous terrain using steel bends, characterized in that... The experimental method includes the following steps: S1. Select the test pipe section as the water pressure test section, and select the two ends of the test pipe section with a steel bend that varies with the terrain by more than 11.25°. S2. Calculate and design the plug plate for the test pipe section according to the formula for calculating the thickness of the plug plate under stress, and seal the end of the water pressure test section with the plug plate; The formula for calculating the thickness of the blocking plate under stress in step S2 is as follows: In the formula: Thickness under stress, mm; P is the design pressure of the plug plate, MPa; Nominal diameter, mm; ρ is the allowable stress of the steel plate at the design temperature, in MPa; Ф is the weld coefficient, taken as 0.85; S3. The steel bends at both ends of the test section and the soil around the steel bends after backfilling are used as natural back walls. The bearing capacity of the soil around the two steel bends is verified by using the allowable resistance formula, the force width formula, and the length formula of the back soil layer to check whether the back wall requirements are met. The allowable resistance formula for the back soil in step S3 is: In the formula: --Passive earth pressure per 1m width, kN / m; --Gross density of the backing soil, kN / m³ 3 c -- Cohesion of the backing soil, kN / m²; H -- Height of the back wall, which can be equivalent to the pipe height difference, m; h -- Height from the top of the back wall to the ground, which can be equivalent to the height from the top of the highest pipe to the ground, m; Kp -- Passive earth pressure coefficient. 2 θ is the internal friction angle of the back soil, taken as 16°, and the calculation is as follows: =1.76; The formula for the force-bearing width of the back soil in step S3 is: B≥2.0 / In the formula: B is the width of the back soil under stress, in meters; The force transmitted from the pipe plug to the back is equal to the total thrust F of the water pressure test, in kN; 2.0 is the safety factor. The length of the back soil layer mentioned in step S3 is: ， In the formula: L is the length along the direction of the force applied to the back, in meters; To add a safety margin, we take 0.5m; S4. After confirming that the bearing capacity of the soil around the two steel bends meets the back wall requirements, install the test equipment in the test pipe section to construct the test system. S5. Subsequently, water injection, air venting, and pressure testing are conducted on the test pipe section, and the quality of pipe installation is judged by the pressure drop or water leakage.

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