Pipe cleaning, pressure testing and baseline detection combined construction method for deep sea composite pipe

Abstract

The invention discloses a pipe cleaning, pressure testing and baseline detection combined construction method for a deep sea composite pipe, which comprises the following steps: injecting fresh water into the composite pipe, keeping the water pressure, and preliminarily cleaning the composite pipe; pipe cleaning operation is conducted, and the composite pipe is cleaned again; performing a pressure test, and checking the sealing performance of the composite pipe; and performing baseline detection to detect metal loss in the composite pipe. Pigging pressure test and baseline detection of original staged construction are integrated into combined construction, a set of efficient, economical and safe submarine pipeline pigging pressure test detection process is formed, meanwhile, the requirement for integrity management of submarine pipelines is met, the construction process is simplified, the construction period is shortened, the construction cost is saved, and the economical efficiency is improved.

Description

Technical Field

[0001] The invention relates to the technical field of submarine pipeline engineering, and in particular to a combined construction method for cleaning, pressure testing and baseline detection of a deep-sea composite pipe. Background Art

[0002] After the construction of submarine pipelines is completed, internal pipeline quality inspections such as cleaning and pressure testing are required. In addition, according to the integrity management requirements of submarine pipelines, baseline testing is required within one year after the oil field is put into production. Generally speaking, conventional carbon steel pipelines are constructed in two stages. The first stage is internal testing for cleaning and pressure testing, and the second stage is baseline testing. Both have relatively mature processes, and seawater can be used as the general medium during the construction process. However, for deep-sea long-distance 316L mechanical composite pipes, due to the special nature of their own materials that are not resistant to seawater corrosion, and the huge amount of engineering work brought about by long-distance construction, it is safest to use fresh water as the medium. At this time, if the conventional two-stage process is used, the construction process will be more complicated and the construction cost will be very high.

[0003] In summary, in the current scheme, the first phase of the cleaning and pressure testing is separate and independent from the second phase of the baseline test. For deep-sea long-distance 316L mechanical composite pipes, the construction period is long, manpower and material resources are consumed, the cost is high, and the economy is low. Summary of the invention

[0004] In view of the above problems, the purpose of the present invention is to provide a joint construction method for cleaning, pressure testing and baseline detection of deep-sea composite pipes, which is used to solve the problem that in the current scheme, the internal detection of cleaning and pressure testing is separated and independent from the baseline detection, and for deep-sea long-distance 316L mechanical composite pipes, the construction period is long, manpower and material resources are consumed, the cost is high, and the economy is low.

[0005] To achieve the above object, the present invention adopts the following technical solutions: The invention discloses a combined construction method for cleaning, pressure testing and baseline detection of a deep-sea composite pipe, comprising: Step A: inject fresh water into the composite pipe and maintain water pressure to perform preliminary cleaning of the composite pipe; Step B: Perform pipe cleaning operation to clean the composite pipe again; Step C: Perform a pressure test to check the sealing performance of the composite pipe; Step D: Perform a baseline test to verify metal loss within the composite pipe.

[0006] Wherein, the composite pipe is a 316L mechanical composite pipe.

[0007] Preferably, the step A comprises the following steps: Step A1: connect the water injection pump on the saturation diving support vessel to the water injection inlet of the starting towing head of the composite pipe through a water injection hose, connect the outlet of the main pipeline of the starting towing head to the inlet of the composite pipe, and connect the outlet of the composite pipe to the inlet of the ending towing head; Step A2: pre-install a foam ball in the main pipe of the starting traction head, and the foam ball is located in the main pipe between the front branch pipe and the middle branch pipe; Step A3: Open the valve on the rear branch pipe of the starting towing head, start the water injection pump, and the saturation diving support vessel injects fresh water into the water inlet of the starting towing head, and the fresh water reaches the ending towing head through the composite pipe; Step A4: Continue to inject fresh water, and the pressure in the composite pipe increases until the injection pressure meets the design requirements; Step A5: Open the valves on the front branch pipe and the middle branch pipe of the starting drag head respectively, and push the foam ball into the composite pipe by water pressure until the foam ball passes through the composite pipe and reaches the ending drag head.

[0008] Preferably, the step B comprises the following steps: Step B1: disassemble the starting traction head and the ending traction head at both ends of the composite pipe, respectively install a ball launching cylinder at one end of the starting traction head of the composite pipe and install a ball receiving cylinder at one end of the ending traction head of the composite pipe; Step B2: Use mechanical straight-plate balls whose outer diameters are 92%, 95% and 97% of the inner diameter of the composite pipe as pipe cleaning balls respectively, and pass the pipe cleaning balls into the composite pipe through the ball-dispensing tube to clean the composite pipe in a progressive manner. The pipe cleaning balls pass through the composite pipe and reach the ball-collecting tube until the pipe cleaning operation is completed.

[0009] Furthermore, after step B2, the method further includes: Step B3: Diameter measurement A mechanical diameter measuring ball is passed into the composite pipe, which not only further cleans the composite pipe but also measures the inner diameter of the composite pipe. During the process, the deformation of the composite pipe is observed and recorded until the diameter measurement operation is completed.

[0010] Preferably, the step C comprises the following steps: Step C1: pressurization; Step C2: Maintain pressure Conduct pressure test on composite pipes. When the pressure reaches the specified test pressure, stop increasing the pressure and start stabilizing the pressure. When the pressure stabilizes, start maintaining the pressure in the pipeline for 24 hours. During the pressure holding period, there is no leakage in the composite pipe, the pressure fluctuation within 24 hours does not exceed ±0.2% of the test pressure, and the pressure at the end of the pressure holding is not lower than the test pressure. If the pressure drop caused by temperature can be within the maximum allowable pressure drop of ±0.4%, the pressure test result is qualified; otherwise, the pressure holding time is extended until it is qualified; Step C3: Pressure relief After the composite pipe passes the pressure maintenance test, the pressure relief in the pipeline begins. The pressure relief rate in the composite pipe is no more than 0.1 MPa / min. During the pressure relief process, the following data are recorded every 15 minutes.

[0011] Preferably, the step C1 comprises the following steps: Step C11: Increase the pressure at a rate not exceeding 0.1 MPa / min. The pressure should be gradually increased to 35% of the test pressure. Stop increasing the pressure and conduct a composite pipe leakage test for 15 minutes. Step C12: Continue to increase the pressure at a rate not exceeding 0.1 MPa / min until the pressure reaches 75% of the test pressure; Step C13: Continue to increase the pressure at a rate not exceeding 0.1 MPa / min until the pressure reaches 95% of the test pressure, maintain the pressure for 15 minutes, reduce the pressure increase rate, and increase the pressure at 0.01 MPa / min for the remaining 5% of the test pressure.

[0012] Preferably, the step D comprises the following steps: Step D1: Before the baseline test, further clean the inside of the composite tube to ensure that the inside of the composite tube is clean; Step D2: Use an ultrasonic detector to detect the metal loss in the composite pipe.

[0013] Preferably, the step D1 comprises the following steps: Step D11: Pass the mechanical nylon brush ball into the composite pipe to further clean the composite pipe until the mechanical nylon brush ball reaches the ball receiving cylinder; Step D12: Pass the mechanical magnet ball into the composite pipe to clean the ferromagnetic impurities inside the composite pipe until the mechanical magnet ball reaches the ball collecting cylinder.

[0014] Compared with the prior art, the present invention has the following beneficial effects: The present invention discloses a combined construction method for cleaning, pressure testing and baseline detection of deep-sea composite pipes, including: injecting fresh water into the composite pipe and maintaining water pressure to perform preliminary cleaning of the composite pipe; performing cleaning operations to clean the composite pipe again; performing pressure testing to check the sealing of the composite pipe; and performing baseline detection to check the metal loss in the composite pipe. The present invention integrates the cleaning pressure testing and baseline detection that were originally constructed in stages, and the two are combined into one, forming a set of efficient, economical and safe submarine pipeline cleaning pressure testing and detection processes, while meeting the requirements for submarine pipeline integrity management. The technical solution of the present invention simplifies the construction process, shortens the construction period, saves construction costs, and improves economy.

[0015] In addition, the present invention also has the following advantages: 1. The existing process generally adopts two-stage construction, which often leads to repeated mobilization, resulting in waste of ship resources, increasing construction costs and weakening economic benefits. From the perspective of economic benefits, the present invention integrates the phased construction into a combined construction, avoiding the waste of ship resources, reducing production costs as a whole and improving economic benefits.

[0016] 2. If the existing process is constructed with fresh water resources, the entire process requires about 5.2 times the pipe capacity of fresh water. If the present invention is used for construction, the fresh water consumption can be reduced to 3.4 times the pipe capacity. For long-distance pipelines, the difference of 1.8 times the pipe capacity is huge, and multiple trips of fresh water transportation are often required. It can be seen that this solution is relatively friendly to fresh water transportation and fresh water consumption, and indirectly helps to reduce costs and increase efficiency.

[0017] 3. In terms of the number of passes and the number of balls, the two-stage separate construction requires 1 foam ball in the horizontal pipe water injection stage, 3 cleaning balls + 1 measuring ball in the cleaning and diameter measuring stage, and 1 cleaning ball + 1 mechanical diameter measuring ball + 1 electronic diameter measuring ball + 1 detection ball in the baseline detection stage. A total of 6 passes are required, with 9 balls. The difference in the combined construction of the present invention is mainly reflected in that the diameter measuring ball in the baseline detection stage follows the diameter measuring ball in the diameter measuring stage, and the balls are sent together and only travel once, that is, the three trips and three diameter measurements in the separate stages are combined into one trip and two diameter measurements. In addition, the cleaning ball in the baseline detection stage is omitted, and a total of 3 passes are required, with 7 balls. A large amount of ball passing time and number of times are saved, and the ball passing efficiency can be effectively improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a schematic structural diagram of the starting drag head provided in Example 1 of the present invention.

[0019] Description of reference numerals: 1- Main pipeline; 2-water injection branch pipe, 20-main valve, 21-front branch pipe, 22-middle branch pipe, 23-rear branch pipe, 24-valve; 3- Foam ball. DETAILED DESCRIPTION

[0020] The exemplary embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. Although the exemplary embodiments of the present invention are shown in the accompanying drawings, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments described herein. On the contrary, these embodiments are provided in order to enable a more thorough understanding of the present invention and to fully convey the scope of the present invention to those skilled in the art.

[0021] In order to solve the problems of complicated process, lengthy time and high cost in long-distance deep-sea cleaning and pressure testing and baseline detection, the present invention integrates the previously phased construction of cleaning and pressure testing and baseline detection into a combined construction, thereby simplifying the construction process, shortening the construction period, saving construction costs and improving economy.

[0022] Example 1: A combined construction equipment for deep-sea composite pipe cleaning, pressure testing and baseline detection Example 1 provides a deep-sea composite pipe cleaning, pressure testing and baseline detection combined construction equipment, which is used to perform cleaning, pressure testing and baseline detection on 316L composite pipes. Its structure is described in detail below with reference to the accompanying drawings.

[0023] The deep-sea composite pipe cleaning, pressure testing and baseline detection joint construction equipment includes a saturation diving support vessel, a water injection hose, a starting towing head, an ending towing head, a ball launching barrel, a ball receiving barrel and several cleaning balls.

[0024] The saturation diving support vessel is equipped with a fresh water tank, and a water injection pump is provided in the fresh water tank.

[0025] refer to Figure 1 , the starting traction head comprises a main pipeline 1, the end of the main pipeline 1 is set as an outlet; The main pipeline 1 is provided with a water injection branch pipe 2 in parallel, and a main valve 20 is provided at the water injection inlet of the water injection branch pipe 2; A front branch pipe 21, a middle branch pipe 22 and a rear branch pipe 23 are arranged in sequence from front to back between the water injection branch pipe 2 and the main pipeline 1. Both ends of each branch pipe are connected to the main pipeline 1 and the water injection branch pipe 2, respectively, and a valve 24 is arranged on the branch pipe. A foam ball 3 is arranged in the main pipe 1 between the front branch pipe 21 and the middle branch pipe 22 .

[0026] A foam ball 3 is pre-installed in the main pipe of the starting traction head. Specifically, the foam ball is installed in the main pipe 1 between the front branch pipe 21 and the middle branch pipe 22 .

[0027] When water injection operation is required, the water injection pump on the saturation diving support vessel is connected to the water injection inlet of the starting towing head of the composite pipe through a water injection hose, the outlet of the main pipeline 1 of the starting towing head is connected to the inlet of the composite pipe, and the outlet of the composite pipe is connected to the inlet of the terminating towing head.

[0028] Open the main valve 20, then open the valve 24 on the rear branch pipe 23, start the water injection pump, and the saturation diving support vessel injects fresh water into the water inlet of the starting towing head. The fresh water passes through the composite pipe and reaches the ending towing head; After the pressure in the composite pipe meets the design requirements, close the valve 24 on the rear branch pipe 23, open the valve 24 on the front branch pipe 21 first, and wait until the foam ball 3 is washed through the main pipeline 1 corresponding to the middle branch pipe 22 by the water flow from the front branch pipe 21, then open the valve 24 on the middle branch pipe 22, and the foam ball 3 passes through the composite pipe under the action of water pressure to reach the termination towing head.

[0029] When it is necessary to carry out the pipe cleaning operation, remove the starting drag head on the composite pipe, replace and install the ball launching cylinder, remove the ending drag head on the composite pipe, and replace and install the ball receiving cylinder.

[0030] Among them, the pipe cleaning ball can be selected from a mechanical straight plate ball whose outer diameter accounts for 92%, 95% and 97% of the inner diameter of the composite pipe.

[0031] The launching barrel is used to launch the pipe cleaning ball, and the collecting barrel is used to collect the pipe cleaning ball. When a pipe cleaning ball launched by the launching barrel passes through the composite pipe and reaches the collecting barrel, one pipe cleaning is completed.

[0032] Example 2: A combined construction method for deep-sea composite pipe cleaning, pressure testing and baseline detection Embodiment 2 provides a deep-sea composite pipe cleaning, pressure testing and baseline detection joint construction method, using the construction equipment of embodiment 1, the construction method comprises the following steps: Step A: Inject fresh water into the composite pipe and maintain water pressure to perform preliminary cleaning of the composite pipe, including the following steps: Step A1: connect the water injection pump on the saturation diving support vessel to the water injection inlet of the starting towing head of the composite pipe through a water injection hose, connect the outlet of the main pipeline of the starting towing head to the inlet of the composite pipe, and connect the outlet of the composite pipe to the inlet of the ending towing head; Step A2: pre-install a foam ball in the main pipe of the starting traction head, and the foam ball is located in the main pipe between the front branch pipe and the middle branch pipe; Step A3: Open the valve on the rear branch pipe of the starting towing head, start the water injection pump, and the saturation diving support vessel injects fresh water into the water inlet of the starting towing head, and the fresh water reaches the ending towing head through the composite pipe; Step A4: Continue to inject fresh water, and the pressure in the composite pipe increases until the injection pressure meets the design requirements; Step A5: Open the valves on the front branch pipe and the middle branch pipe of the starting drag head respectively, and push the foam ball into the composite pipe by water pressure until the foam ball passes through the composite pipe and reaches the ending drag head.

[0033] Wherein, the composite pipe is a 316L mechanical composite pipe.

[0034] Step B: Perform a pipe cleaning operation to clean the composite pipe again, including the following steps: Step B1: disassemble the starting traction head and the ending traction head at both ends of the composite pipe, respectively install a ball launching cylinder at one end of the starting traction head of the composite pipe and install a ball receiving cylinder at one end of the ending traction head of the composite pipe; Step B2: Use mechanical straight-plate balls whose outer diameters are 92%, 95% and 97% of the inner diameter of the composite pipe as pipe cleaning balls respectively, and pass the pipe cleaning balls into the composite pipe through the ball-dispensing tube to clean the composite pipe in a progressive manner. The pipe cleaning balls pass through the composite pipe and reach the ball-collecting tube until the pipe cleaning operation is completed.

[0035] In order to observe the deformation of the composite pipe, after step B2, the following steps are further included: Step B3: Diameter measurement A mechanical diameter measuring ball is passed into the composite pipe, which not only further cleans the composite pipe but also measures the inner diameter of the composite pipe. During the process, the deformation of the composite pipe is observed and recorded until the diameter measurement operation is completed.

[0036] Step C: Perform a pressure test to check the sealing of the composite pipe, including the following steps: Step C1: pressurization, including the following steps: Step C11: Increase the pressure at a rate not exceeding 0.1 MPa / min. The pressure should be gradually increased to 35% of the test pressure. Stop increasing the pressure and conduct a composite pipe leakage test for 15 minutes. Step C12: Continue to increase the pressure at a rate not exceeding 0.1 MPa / min until the pressure reaches 75% of the test pressure; Step C13: Continue to increase the pressure at a rate not exceeding 0.1 MPa / min until the pressure reaches 95% of the test pressure, maintain the pressure for 15 minutes, reduce the pressure increase rate, and increase the pressure at 0.01 MPa / min for the remaining 5% of the test pressure.

[0037] Step C2: Maintain pressure Conduct pressure test on composite pipes. When the pressure reaches the specified test pressure, stop increasing the pressure and start stabilizing the pressure. When the pressure stabilizes, start maintaining the pressure in the pipeline for 24 hours. During the pressure holding period, there is no leakage in the composite pipe, the pressure fluctuation within 24 hours does not exceed ±0.2% of the test pressure, and the pressure at the end of the pressure holding is not lower than the test pressure. If the pressure drop caused by temperature can be within the maximum allowable pressure drop of ±0.4%, the pressure test result is qualified; otherwise, the pressure holding time is extended until it is qualified; Step C3: Pressure relief After the composite pipe passes the pressure maintenance test, the pressure relief in the pipeline begins. The pressure relief rate in the composite pipe is no more than 0.1 MPa / min. During the pressure relief process, the following data are recorded every 15 minutes.

[0038] Step D: Perform a baseline test to verify metal loss in the composite pipe, including the following steps: Step D1: Before the baseline test, further clean the inside of the composite pipe to ensure that the inside of the composite pipe is clean, including the following steps: Step D11: Pass the mechanical nylon brush ball into the composite pipe to further clean the composite pipe until the mechanical nylon brush ball reaches the ball receiving cylinder; Step D12: Pass the mechanical magnet ball into the composite pipe to clean the ferromagnetic impurities inside the composite pipe until the mechanical magnet ball reaches the ball collecting cylinder.

[0039] Step D2: Use an ultrasonic detector to detect the metal loss in the composite pipe.

[0040] Example 3: An application example of combined construction of deep-sea composite pipe cleaning, pressure testing and baseline detection Example 3 takes the Wenchang 16-2 oilfield development project as an example, and applies the combined construction method of Example 2 to the project, and conducts long-distance submarine pipeline cleaning, pressure testing and baseline detection construction through fresh water. The main effect is reflected in the integration and reorganization of effective steps to form a set of efficient, economical and safe submarine pipeline cleaning, pressure testing and detection processes, while meeting the requirements for submarine pipeline integrity management.

[0041] In order to prevent seawater from entering the 316L mechanical composite pipe and causing pipeline corrosion problems, First, mobilize a freshwater transport ship to the operation area to start water injection in the horizontal pipe section, and then inject water into the horizontal pipe section and pass a foam ball to carry out preliminary cleaning; Secondly, the cleaning and diameter measurement process was carried out, and three cleaning balls were launched; Next, the overall pressure test is carried out, after pressure filling, pressure maintenance and pressure relief, Then, two mechanical caliper balls are launched (one is the mechanical caliper ball used in the cleaning phase of the original plan, and the other is the mechanical caliper ball used in the baseline detection phase; the diameter of the former caliper ball is slightly smaller than that of the latter); Finally, an ultrasonic test ball is fired to conduct a baseline test.

[0042] The effect of the above steps is reflected in: avoiding the complicated procedures and huge fresh water consumption caused by repeated diameter measurement, and forming a set of efficient, economical and safe submarine pipeline cleaning and pressure testing processes by integrating and reorganizing effective steps, while meeting the requirements of submarine pipeline integrity management.

[0043] The main purpose of the scheme of the present invention is to integrate the relevant processes of freshwater cleaning pressure testing and baseline testing of deep-sea long-distance 316L mechanical composite pipes, so as to reduce the construction complexity caused by the seawater resistance of 316L mechanical composite pipes, save freshwater resources, and ultimately solve the problem of high construction cost.

[0044] 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 embodiments of the present invention.

Claims

1. A combined construction method for cleaning, pressure testing and baseline detection of deep-sea composite pipes, characterized in that: include Step A: inject fresh water into the composite pipe and maintain water pressure to perform preliminary cleaning of the composite pipe; Step B: Perform pipe cleaning operation to clean the composite pipe again; Step C: Perform a pressure test to check the sealing performance of the composite pipe; Step D: Perform a baseline test to verify metal loss within the composite pipe.

2. The combined construction method according to claim 1, characterized in that: The composite pipe is a 316L mechanical composite pipe.

3. The combined construction method according to claim 1, characterized in that: The step A comprises the following steps: Step A1: connect the water injection pump on the saturation diving support vessel to the water injection inlet of the starting towing head of the composite pipe through a water injection hose, connect the outlet of the main pipeline of the starting towing head to the inlet of the composite pipe, and connect the outlet of the composite pipe to the inlet of the ending towing head; Step A2: pre-install a foam ball in the main pipe of the starting traction head, and the foam ball is located in the main pipe between the front branch pipe and the middle branch pipe; Step A3: Open the valve on the rear branch pipe of the starting towing head, start the water injection pump, and the saturation diving support vessel injects fresh water into the water inlet of the starting towing head, and the fresh water reaches the ending towing head through the composite pipe; Step A4: Continue to inject fresh water, and the pressure in the composite pipe increases until the injection pressure meets the design requirements; Step A5: Open the valves on the front branch pipe and the middle branch pipe of the starting drag head respectively, and push the foam ball into the composite pipe by water pressure until the foam ball passes through the composite pipe and reaches the ending drag head.

4. The combined construction method according to claim 1, characterized in that: The step B comprises the following steps: Step B1: disassemble the starting traction head and the ending traction head at both ends of the composite pipe, respectively install a ball launching cylinder at one end of the starting traction head of the composite pipe and install a ball receiving cylinder at one end of the ending traction head of the composite pipe; Step B2: Use mechanical straight-plate balls whose outer diameters are 92%, 95% and 97% of the inner diameter of the composite pipe as pipe cleaning balls respectively, and pass the pipe cleaning balls into the composite pipe through the ball-dispensing tube to clean the composite pipe in a progressive manner. The pipe cleaning balls pass through the composite pipe and reach the ball-collecting tube until the pipe cleaning operation is completed.

5. The combined construction method according to claim 4, characterized in that: After step B2, the method further includes: Step B3: Diameter measurement A mechanical diameter measuring ball is passed into the composite pipe, which not only further cleans the composite pipe but also measures the inner diameter of the composite pipe. During the process, the deformation of the composite pipe is observed and recorded until the diameter measurement operation is completed.

6. The combined construction method according to claim 1, characterized in that: The step C comprises the following steps: Step C1: pressurization; Step C2: Maintain pressure Conduct pressure test on composite pipes. When the pressure reaches the specified test pressure, stop increasing the pressure and start stabilizing the pressure. When the pressure stabilizes, start maintaining the pressure in the pipeline for 24 hours. Step C3: Pressure relief After the composite pipe passes the pressure maintenance test, the pressure relief in the pipeline begins. The pressure relief rate in the composite pipe is no more than 0.1 MPa / min. During the pressure relief process, the following data are recorded every 15 minutes.

7. The combined construction method according to claim 6, characterized in that: In step C2, during the pressure holding period, there is no leakage in the composite pipe, the pressure fluctuation within 24 hours does not exceed ±0.2% of the test pressure, and the pressure at the end of the pressure holding is not lower than the test pressure. If the pressure drop caused by temperature can be within the maximum allowable pressure drop of ±0.4%, the pressure test result is qualified; otherwise, the pressure holding time is extended until it is qualified.

8. The combined construction method according to claim 6, characterized in that: The step C1 comprises the following steps: Step C11: Increase the pressure at a rate not exceeding 0.1 MPa / min. The pressure should be gradually increased to 35% of the test pressure. Stop increasing the pressure and conduct a composite pipe leakage test for 15 minutes. Step C12: Continue to increase the pressure at a rate not exceeding 0.1 MPa / min until the pressure reaches 75% of the test pressure; Step C13: Continue to increase the pressure at a rate not exceeding 0.1 MPa / min until the pressure reaches 95% of the test pressure, maintain the pressure for 15 minutes, reduce the pressure increase rate, and increase the pressure at 0.01 MPa / min for the remaining 5% of the test pressure.

9. The combined construction method according to claim 1, characterized in that: The step D comprises the following steps: Step D1: Before the baseline test, further clean the inside of the composite tube to ensure that the inside of the composite tube is clean; Step D2: Use an ultrasonic detector to detect the metal loss in the composite pipe.

10. The combined construction method according to claim 9, characterized in that: The step D1 comprises the following steps: Step D11: Pass the mechanical nylon brush ball into the composite pipe to further clean the composite pipe until the mechanical nylon brush ball reaches the ball receiving cylinder; Step D12: Pass the mechanical magnet ball into the composite pipe to clean the ferromagnetic impurities inside the composite pipe until the mechanical magnet ball reaches the ball collecting cylinder.

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