Method for determining the critical gas operating pressure for collapse of non-bonded composite pipe lining

Abstract

This invention discloses a method for determining the critical gas operating pressure for the collapse of the lining of a non-bonded composite pipe. The method involves obtaining the interlayer volume, operating temperature, operating time, and transported gas composition between the reinforcing layer and the lining layer of the non-bonded composite pipe; testing the gas permeability coefficients of the lining layer and the outer protective layer based on the operating temperature and transported gas composition; inputting the interlayer volume, operating temperature, operating time, gas permeability coefficients of the lining layer and the outer protective layer into a pre-constructed interlayer permeability pressure model to obtain the interlayer permeability pressure between the reinforcing layer and the lining layer; determining the radial collapse pressure of the lining layer; and inputting the interlayer permeability pressure and radial collapse pressure into a pre-constructed critical collapse failure criterion model to obtain the critical gas operating pressure for the collapse of the lining of the non-bonded composite pipe. This invention can determine the critical gas operating pressure of a non-bonded composite pipe.

Description

Technical Field

[0001] This invention belongs to the field of non-metallic composite pipe performance testing technology, specifically relating to a method for determining the critical gas operating pressure for the collapse of the lining of a non-bonded composite pipe. Background Technology

[0002] Pipelines are one of the key pieces of equipment for oil and gas extraction and transportation. With the rapid development of the materials industry, pipelines using new materials and structural forms are constantly emerging. Among them, reinforced thermoplastic continuous pipes have maintained rapid growth in usage due to their excellent corrosion resistance, and their usage in some oil fields has even exceeded 50%. Reinforced thermoplastic continuous pipes are usually composed of multi-layer composite structures and can be divided into non-bonded composite pipes and bonded composite pipes according to their cross-sectional structure.

[0003] Non-bonded composite pipes are composite pipes made by reinforcing a thermoplastic inner lining (such as high-density polyethylene, heat-resistant polyethylene, PERT, nylon PA, polyvinylidene fluoride, PVDF, etc.) with continuous fiber filaments (ribbons) or steel wire (ribbons) as reinforcement materials through winding, braiding, or other methods. The pipe body of a non-bonded composite pipe consists of a layered inner lining 24, a reinforcing layer 25, and an outer protective layer 26, which are sequentially wrapped together (e.g., Figure 1 During deformation, relative displacement can occur between the layers. This type of product has been widely used in oil and gas fields due to its advantages such as simple manufacturing process, high production efficiency, and good product flexibility.

[0004] During service, non-bonded composite pipes with thermoplastic linings are susceptible to permeation by various gases dissolved in petroleum media, such as CH4, H2S, and CO2, through adsorption and diffusion on the inner surface of the thermoplastic pipe. These gases gradually accumulate in the interlayer between the thermoplastic lining and the reinforcing layer. When the pipeline is shut down, experiences internal pressure fluctuations, or suffers a sudden negative pressure, the external pressure generated by the accumulated gas in the interlayer can cause the thermoplastic pipe to collapse and fail. Harsh oil and gas gathering and transportation conditions, such as high-temperature and high-pressure environments, accelerate the gas permeation process, increasing the total amount of gas permeating into the interlayer and further increasing the risk of radial collapse failure of the thermoplastic pipe.

[0005] With the composition of the transported gas, operating temperature, thermoplastic material and specifications already determined, most oilfield users are concerned about how to determine the critical gas operating pressure of the non-bonded composite pipe. This is to guide the optimization of the pipeline's operating pressure parameters, control the total amount of gas permeating into the interlayer, and thus prevent the collapse and failure of the inner lining of the non-bonded composite pipe from the source. Summary of the Invention

[0006] To address the problems existing in the prior art, this invention provides a method for determining the critical gas operating pressure for the collapse of the lining of a non-bonded composite pipe. This method can determine the critical gas operating pressure of the non-bonded composite pipe, thereby guiding the optimization of the pipeline's operating pressure parameters, controlling the total amount of gas permeating into the interlayer, and thus preventing the collapse failure of the lining of the non-bonded composite pipe from the source.

[0007] To solve the above-mentioned technical problems, the present invention is achieved through the following technical solution:

[0008] A method for determining the critical gas operating pressure for the collapse of a non-bonded composite pipe lining includes:

[0009] The volume of the interlayer between the reinforcing layer and the inner lining layer of the non-bonded composite pipe, the operating temperature of the non-bonded composite pipe, the operating time of the non-bonded composite pipe, and the composition of the gas transported by the non-bonded composite pipe are obtained.

[0010] Based on the operating temperature and the composition of the transported gas, the gas permeability coefficient of the inner lining of the non-bonded composite pipe and the gas permeability coefficient of the outer protective layer of the non-bonded composite pipe were tested respectively.

[0011] The interlayer volume, operating temperature, operating time, gas permeability coefficient of the inner lining layer, and gas permeability coefficient of the outer protective layer are input into a pre-constructed interlayer permeability pressure model between the non-bonded composite pipe reinforcement layer and the inner lining layer to obtain the interlayer permeability pressure between the non-bonded composite pipe reinforcement layer and the inner lining layer.

[0012] Determine the radial collapse pressure of the non-bonded composite pipe liner;

[0013] The interlayer permeation pressure and the radial collapse pressure are input into a pre-constructed critical collapse failure criterion model to obtain the critical gas operating pressure for the collapse of the non-bonded composite pipe lining.

[0014] Furthermore, the interlayer osmotic pressure model is specifically as follows:

[0015]

[0016] in,

[0017] In the formula, P a P1 is the interlayer permeation pressure; P2 is the critical gas operating pressure; R is the molar gas constant; T is the operating temperature; V is the interlayer volume; t is the operating time; C1 is the gas permeability coefficient of the inner lining; C2 is the gas permeability coefficient of the outer protective layer; D1 is the diameter of the inner lining; D2 is the diameter of the outer protective layer; l1 is the wall thickness of the inner lining; l2 is the wall thickness of the outer protective layer.

[0018] Furthermore, the critical collapse failure criterion model is specifically as follows:

[0019] P a =P1+P c

[0020] In the formula, P c This refers to the radial collapse pressure of the inner lining of a non-bonded composite pipe.

[0021] Furthermore, the step of testing the gas permeability coefficient of the inner lining of the non-bonded composite pipe and the gas permeability coefficient of the outer protective layer of the non-bonded composite pipe based on the operating temperature and the composition of the transported gas specifically includes:

[0022] A first thermoplastic film sample was prepared using the same raw material as the inner lining of the non-bonded composite pipe, and a second thermoplastic film sample was prepared using the same raw material as the outer protective layer of the non-bonded composite pipe.

[0023] The gas permeation test temperature is set to the operating temperature. A gas permeameter is used to test the gas permeation coefficient of the transported gas component in the first thermoplastic film sample, which is the gas permeation coefficient of the inner lining of the non-adhesive composite pipe. The gas permeation coefficient of the transported gas component in the second thermoplastic film sample is also tested, which is the gas permeation coefficient of the outer protective layer of the non-adhesive composite pipe.

[0024] Furthermore, the preparation process of the first thermoplastic film sample is the same as the preparation process of the non-adhesive composite pipe liner.

[0025] The preparation process of the second thermoplastic film sample is the same as that of the preparation process of the outer protective layer of the non-adhesive composite pipe.

[0026] Furthermore, determining the radial collapse pressure of the non-bonded composite pipe liner specifically includes:

[0027] Environmental simulation tests were conducted on the test samples of the non-bonded composite pipe.

[0028] Radial pressure tests were conducted on the inner lining of the unbonded composite pipe test sample, and the changes in interlayer pressure between the reinforcing layer and the inner lining of the unbonded composite pipe sample were recorded.

[0029] Based on the change in interlayer pressure between the reinforcing layer and the inner lining layer of the unbonded composite pipe sample, plot the curve of the interlayer pressure change between the reinforcing layer and the inner lining layer of the unbonded composite pipe sample.

[0030] The radial collapse pressure of the inner lining of the non-bonded composite pipe is obtained from the interlayer pressure variation curve.

[0031] Furthermore, when conducting radial pressure tests on the inner lining of the non-bonded composite pipe test sample, the pressure rate is controlled between 0.1 MPa / s and 0.5 MPa / s.

[0032] Furthermore, the formula for calculating the interlayer volume between the reinforcing layer and the inner lining layer of the non-bonded composite pipe is as follows:

[0033] Interlayer volume = outer surface area of ​​inner lining layer × thickness of reinforcing layer × (1 - volume fraction of reinforcing layer);

[0034] The volume fraction of the reinforcing layer was obtained by Archimedes' method of water displacement.

[0035] Furthermore, when there are fluctuations or negative pressure in the operating pressure of the non-bonded composite pipe, the radial collapse pressure should be corrected, with a correction factor of 0.5 to 0.8.

[0036] Compared with the prior art, the present invention has at least the following beneficial effects: The present invention provides a method for determining the critical gas operating pressure for the collapse of the lining of a non-bonded composite pipe. Based on the operating temperature and the composition of the transported gas, the gas permeability coefficients of the lining and the outer protective layer of the non-bonded composite pipe are tested. The interlayer volume, operating temperature, operating time, gas permeability coefficients of the lining and the outer protective layer are input into a pre-constructed interlayer permeability pressure model between the reinforcing layer and the lining of the non-bonded composite pipe to obtain the interlayer permeability pressure between the reinforcing layer and the lining. The radial collapse pressure of the lining of the non-bonded composite pipe is determined. The interlayer permeability pressure and the radial collapse pressure are input into a pre-constructed critical collapse failure criterion model to obtain the critical gas operating pressure for the collapse of the lining of the non-bonded composite pipe. This invention considers both the gas permeation problem leading to the collapse of the lining of an unbonded composite pipe and the collapse resistance of the lining itself. It uses a permeation pressure model between the reinforcing layer and the lining to obtain the permeation pressure between them. Finally, it uses a critical collapse failure criterion model to obtain the critical gas operating pressure for the lining to collapse. The calculation results are intuitive, reliable, and highly instructive. This invention calculates and determines whether the lining of an unbonded composite pipe is at risk of collapse after a period of operation. Furthermore, by testing the gas permeability coefficients of different transported gas components in the lining and the outer protective layer of the unbonded composite pipe, this invention can estimate the critical operating pressures of different gases that could cause the lining to collapse under actual operating conditions.

[0037] The radial collapse pressure test method of the non-bonded composite pipe lining of this invention is reasonably designed, intuitive to test, and easy to operate. It can also simulate the service conditions of full-size composite pipe products in oil and gas transportation environments to the greatest extent. Temperature, pressure, gas composition, and liquid medium can all be adjusted. The test sample can be rotated, and the test data obtained are accurate and reliable.

[0038] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, preferred embodiments are described below in detail with reference to the accompanying drawings. Attached Figure Description

[0039] To more clearly illustrate the technical solutions in the specific embodiments of the present invention, the drawings used in the description of the specific embodiments will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0040] Figure 1 This is a gas permeation model for non-bonded composite pipes.

[0041] Figure 2 This is a schematic diagram of a thermoplastic liner tube collapse pressure testing system.

[0042] Figure 3 The radial collapse pressure test curve is for thermoplastic plastic liner tubes.

[0043] In the diagram: 1-Transfer connector; 2-Pressure gauge; 3-Thermoplastic inner liner; 4-Sealing plug; 5-Flange; 6-Fastening screw; 7-Steel base pipe; 8-Water inlet; 9-Pressure hose; 10-Pressure pump; 11-Nut; 12-Inlet valve; 13-Pressure relief valve; 14-Pressure sensor connection port; 15-Data acquisition system; 16-Pressure sensor; 17-Pressure pipe; 18-Gas cylinder; 19-Conveyor belt; 20-Motor; 21-Environmental test chamber; 22-Support base; 23-Waste gas treatment system; 24-Inner liner; 25-Reinforcing layer; 26-Outer protective layer. Detailed Implementation

[0044] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0045] As a specific embodiment of the present invention, a method for determining the critical gas operating pressure for the collapse of a non-bonded composite pipe lining specifically includes the following steps:

[0046] Step 1: Obtain the interlayer volume V between the reinforcing layer and the inner lining layer of the non-bonded composite pipe (in this invention, the interlayer volume is the volume of the void between the reinforcing layer and the inner lining layer of the non-bonded composite pipe), the operating temperature T of the non-bonded composite pipe, the operating time t of the non-bonded composite pipe, and the gas composition transported by the non-bonded composite pipe; generally, the gas composition transported includes CH4, CO2, O2, N2, and H2S.

[0047] Specifically, the formula for calculating the interlayer volume between the reinforcing layer and the inner lining layer of the non-bonded composite pipe is as follows:

[0048] The interlayer volume V = outer surface area of ​​the inner lining layer × thickness of the reinforcing layer × (1 - volume fraction of the reinforcing layer)

[0049] The volume fraction of the reinforcing layer was determined by Archimedes' method of drainage.

[0050] Step 2: Based on the operating temperature and the composition of the transported gas, test the gas permeability coefficient C1 of the inner lining of the non-bonded composite pipe and the gas permeability coefficient C2 of the outer protective layer of the non-bonded composite pipe.

[0051] As a preferred embodiment, testing the gas permeability coefficient C1 of the inner lining of the non-bonded composite pipe and the gas permeability coefficient C2 of the outer protective layer of the non-bonded composite pipe specifically includes the following steps:

[0052] Step a: Prepare a first thermoplastic film sample using the same raw material as the inner lining of the non-bonded composite pipe, and prepare a second thermoplastic film sample using the same raw material as the outer protective layer of the non-bonded composite pipe.

[0053] The preparation process of the first thermoplastic film sample is the same as that of the preparation process of the inner lining of the non-adhesive composite pipe; the preparation process of the second thermoplastic film sample is the same as that of the preparation process of the outer protective layer of the non-adhesive composite pipe.

[0054] Step b: Set the gas permeation test temperature to the operating temperature of the non-bonded composite pipe. Referring to GB / T 1038, use a gas permeameter to test the gas permeation coefficient of the transported gas component in the first thermoplastic film sample, which is the gas permeation coefficient C1 of the inner lining of the non-bonded composite pipe. Test the gas permeation coefficient of the transported gas component in the second thermoplastic film sample, which is the gas permeation coefficient C2 of the outer protective layer of the non-bonded composite pipe.

[0055] Step 3: Input the interlayer volume V, operating temperature T, operating time t, gas permeability coefficient C1 of the inner liner, and gas permeability coefficient C2 of the outer protective layer into the pre-constructed interlayer permeability pressure model between the non-bonded composite pipe reinforcement layer and the inner liner to obtain the interlayer permeability pressure P between the non-bonded composite pipe reinforcement layer and the inner liner. a ;

[0056] Interlayer osmotic pressure P a The calculation formula is f(T,t,C1,C2,P1,V). Specifically, the interlayer permeability pressure model is as follows:

[0057]

[0058] in,

[0059] In the formula, P a P1 is the interlayer permeation pressure; P2 is the critical gas operating pressure; R is the molar gas constant; T is the operating temperature; V is the interlayer volume; t is the operating time; C1 is the gas permeability coefficient of the inner lining; C2 is the gas permeability coefficient of the outer protective layer; D1 is the diameter of the inner lining; D2 is the diameter of the outer protective layer; l1 is the wall thickness of the inner lining; l2 is the wall thickness of the outer protective layer.

[0060] Step 4: Determine the radial collapse pressure P of the unbonded composite pipe liner. c .

[0061] As a preferred embodiment, the radial collapse pressure P of the non-bonded composite pipe liner is determined. c Specifically, it includes:

[0062] Environmental simulation tests were conducted on the test samples of the non-bonded composite pipe.

[0063] A radial pressure test was conducted on the inner lining of the unbonded composite pipe test sample, and the pressure change between the reinforcing layer and the inner lining of the unbonded composite pipe sample was recorded. Preferably, the pressure rate was controlled between 0.1 MPa / s and 0.5 MPa / s when the radial pressure test was conducted on the inner lining of the unbonded composite pipe test sample.

[0064] Based on the change in interlayer pressure between the reinforcing layer and the inner lining layer of the unbonded composite pipe sample, plot the curve of the interlayer pressure change between the reinforcing layer and the inner lining layer of the unbonded composite pipe sample.

[0065] The radial collapse pressure of the inner lining of the unbonded composite pipe is obtained from the interlayer pressure variation curve, such as... Figure 3 As shown, the pressure corresponding to the highest peak of the interlayer pressure variation curve is the radial collapse pressure of the non-bonded composite pipe liner.

[0066] To be more specific, such as Figure 2 As shown, in this embodiment, the non-bonded composite pipe test sample is a thermoplastic plastic-lined composite steel pipe test sample. The thermoplastic plastic-lined composite steel pipe test sample is constructed by inserting a thermoplastic plastic liner 3, which is of the same material and dimensions as the non-bonded composite pipe liner, into a steel base pipe 7. The gap between the thermoplastic plastic liner 3 and the steel base pipe 7 is the interlayer. Preferably, the length of the non-bonded composite pipe test sample is at least greater than 5 times the outer diameter, and the end of the thermoplastic plastic liner 3 is 15-30 mm longer than the steel base pipe 7.

[0067] like Figure 2 As shown, in this embodiment, a method for determining the radial collapse pressure P of an unbonded composite pipe liner is provided. c The testing system includes test samples, end sealing system, interlayer pressure testing system, interlayer pressure monitoring system, and oil and gas working condition environment simulation test system.

[0068] In the testing system, both ends of the test sample are sealed by sealing plugs 4 inserted into thermoplastic inner tubes 3 and sealed with sealing rings. The intermediate connector 1 is connected to the sealing plugs 4 via a threaded connection. The intermediate connector 1 is equipped with a pressure gauge 2, an inlet valve 12, and a pressure relief valve 13 to control the internal pressure build-up or depressurization of the test sample during environmental simulation testing. The intermediate connector 1 also has an internal through-hole for connecting to external gas cylinders, vacuum pumps, or pressure circulation pumps.

[0069] In the testing system, the steel base pipe 7 is sealed at both ends with flanges 5 and sealing rings. The flanges 5 at both ends of the test sample are connected by fastening bolts 6 and tightened with nuts 11. A water inlet 8 and a pressure sensor connection port 14 are provided on the steel base pipe 7. The pressure pump 10 is connected to the water inlet 8 via a pressure hose 9, enabling pressure testing of the test sample's interlayer. The data acquisition system 15 is connected to the pressure sensor connection port 14 via a pressure sensor 16 to monitor interlayer pressure changes in real time and collect pressure change curves.

[0070] In use, one end of the test sample is sealed with a sealing plug 4. The liquid medium (such as oil, water, on-site oilfield concentrate, or laboratory-prepared simulated concentrate) is then placed into the test sample, and the other end is sealed with the sealing plug 4. The intermediate connector 1 connected to the sealing plug 4 is connected to the pressure pipe 17 and the gas cylinder 18 through an internal through-hole. Pressurizing the test sample is achieved by closing the pressure relief valve 13 and opening the air inlet valve 12. After the test sample reaches the set pressure, the air inlet valve 12 is closed, and the entire test sample containing the liquid medium and maintaining a certain internal pressure is placed on the support base 22 and pushed into the environmental test chamber 21. The environmental test chamber 21 uses air heating to achieve temperature rise, temperature preservation, and constant temperature with air circulation. The intermediate connector 1 connected to the sealing plug 4 can be connected to the motor 20 via the conveyor belt 19. Starting the motor 20 drives the test sample to rotate. Preferably, the motor speed is 10–50 r / min, ensuring full contact between the inner wall of the thermoplastic liner and the liquid medium, thus achieving dynamic simulation testing. The test cycle should be 2 days, 7 days, or 14 days. After setting the corresponding test parameters (such as pressure, temperature, time, and speed), the oil and gas environment simulation test of the thermoplastic liner can be completed. Subsequently, the connection... Figure 2 The sandwich pressure testing system and sandwich pressure monitoring system shown can be used to conduct radial collapse pressure tests on thermoplastic liner pipes. The gas produced after the test is safely treated through the exhaust gas treatment system 23.

[0071] In summary, the radial collapse pressure P of the non-bonded composite pipe liner in this embodiment... c The specific testing steps are as follows:

[0072] 1) The thermoplastic plastic lining pipe to be used in the non-bonded composite pipe is inserted into the steel base pipe according to the traditional internal insertion process, so as to prepare the test sample of thermoplastic plastic lining composite steel pipe;

[0073] 2) Based on the specifications and dimensions of the test sample (outer diameter, inner diameter, wall thickness), design the end sealing system of the test sample, and set up a sandwich pressure testing system and a sandwich pressure monitoring system in the middle part of the steel base pipe layer of the test sample.

[0074] 3) After placing the oil-water medium into the test sample, seal it with an end sealing device and place it in an environmental test chamber to establish the field application conditions of the thermoplastic plastic-lined composite steel pipe (heated to a certain temperature and dynamic operation) and carry out environmental simulation tests.

[0075] 4) After the environmental simulation test is completed, connect the test sample to the interlayer pressure testing system and the interlayer pressure monitoring system, conduct the interlayer pressure test, record the interlayer pressure changes, analyze the interlayer pressure change curve, and determine the radial collapse pressure P of the thermoplastic plastic liner pipe under the simulated working conditions. c .

[0076] Preferably, when there are fluctuations or negative pressure in the operating pressure of the non-bonded composite pipe, the radial collapse pressure should be corrected, with a correction factor of 0.5 to 0.8.

[0077] Step 5: Input the interlayer permeation pressure and radial collapse pressure into the pre-constructed critical collapse failure criterion model to obtain the critical gas operating pressure for the collapse of the non-bonded composite pipe lining;

[0078] Combination Figure 1 As shown, when P a >P1+P c When the lining layer collapses, the critical collapse failure criterion model is obtained as follows:

[0079] P a =P1+P c .

[0080] To explain the interlayer permeation pressure model between the reinforcing layer and the inner lining layer of the non-bonded composite pipe in more detail, the following explanation is provided:

[0081] The formula for controlling the amount of gas permeation can be derived from Fick's first law:

[0082]

[0083] Where: Q is the gas permeation rate; A is the surface area; P is the pipeline operating pressure; l is the wall thickness of the thermoplastic lining; C is the gas permeability coefficient; and t is time.

[0084] like Figure 1 As shown, since the reinforcing layer is a loose, unbonded structure, the interlayer permeation pressure P between the reinforcing layer and the inner liner is... a This can be equivalent to the pressure within the entire void space of the reinforcing layer. The interlayer permeation pressure P in the reinforcing layer (or interlayer) a It is determined by the difference between the amount of gas permeating through the inner liner (dQ1) ​​and the amount of gas entering the air from the outer protective layer (dQ2):

[0085]

[0086] Where: Q is the gas permeation rate; P1 is the critical gas operating pressure; P a L is the interlayer permeation pressure; L1 is the inner lining wall thickness; C1 is the gas permeability coefficient of the inner lining; D1 is the inner lining diameter; P2 is atmospheric pressure (0.1 MPa); L2 is the outer protective layer wall thickness; C2 is the outer protective layer gas permeability coefficient; D2 is the outer protective layer diameter; R is the molar gas constant; T is the operating temperature; V is the interlayer volume (the volume of the voids in the reinforcing layer).

[0087]

[0088] in:

[0089] By rearranging equation (3), we get:

[0090]

[0091] set up:

[0092]

[0093]

[0094] Then equation (4) is:

[0095]

[0096] When t = 0, P a =0, therefore E=C

[0097] Substituting the above parameters, we get:

[0098]

[0099] in:

[0100] Example 1

[0101] The critical gas operating pressure at 40℃ for the collapse of the inner lining of a DN100mm non-bonded composite pipe (nylon inner lining + polyester fiber reinforcement layer + polyethylene outer protective layer) transporting CH4 gas is determined as follows:

[0102] (1) Gas permeability coefficient test: Film (sheet) samples with a thickness of 0.1 mm to 0.5 mm were prepared using the same raw materials as the nylon inner liner and the polyethylene outer protective layer. The test temperature was set to 40℃. Referring to GB / T 1038, the permeability coefficients of CH4 gas in the nylon and polyethylene film (sheet) samples were tested using a gas permeation analyzer to determine the C1 and C2 values.

[0103] (2) Establish the formula for calculating the interlayer permeation pressure: As shown in formula (5), test the wall thickness l1 of the inner lining of the DN100mm non-bonded composite pipe, the diameter D1 of the inner lining pipe, the wall thickness l2 of the outer protective layer, the diameter D2 of the outer protective layer, and the thickness l3 of the reinforcing layer. Under the condition that C1 and C2, R (molar gas constant, known), T (pipeline operating temperature 313K), and V (interlayer volume) can be measured or calculated, the interlayer permeation pressure P a The expression for the critical gas operating pressure P1 can be derived from equation (5):

[0104]

[0105] As can be seen from the above formula, the permeation pressure P of the non-bonded composite pipe interlayer a It is a function related to the critical gas operating pressure P1 and the operating time t.

[0106] (3) Radial collapse pressure test of nylon liner: A 1200mm long non-bonded composite pipe was cut, and the nylon liner was removed. A steel base pipe was machined according to its outer diameter. The nylon liner was inserted into the steel base pipe to make a nylon-lined steel pipe test sample. After machining off about 15-30mm of the steel base pipe at both ends, an inlet was opened in the middle of the steel base pipe layer of the nylon-lined steel pipe test sample. A pressure sensor connection port was opened perpendicular to the inlet. According to the specifications of the nylon liner, a sealing plug was designed and installed. The intermediate connector with an air inlet valve, a pressure relief valve and a pressure gauge was connected to the sealing plug, and then the flange was fitted in. The flanges at both ends of the test sample were fastened with bolts. The entire test sample was placed on the support and pushed into the environmental test chamber. The temperature of the environmental test chamber was raised to 40℃, and the environmental simulation test timing was started. After the set test time (e.g., 168 hours) is reached, the environmental simulation test is stopped. The test sample is placed in the environmental test chamber at a constant temperature of 40°C, and the interlayer pressurization system and interlayer pressure monitoring system are connected. The pressure pump is turned on, and the interlayer is pressurized at a rate of 0.2 MPa / s, recording the pressure changes. When the interlayer pressure reaches a certain level... Figure 3 When the pressure changes as shown, stop pressurizing. The inflection point of the pressure change curve is the collapse pressure P of the non-bonded composite pipe nylon liner at 40℃. c .

[0107] (4) Calculation of critical gas operating pressure for nylon liner tube collapse: When the interlayer permeation pressure (P) a > Critical gas operating pressure (P1) + Nylon liner tube collapse resistance pressure (P) c When P occurs, the inner liner tube collapses and fails. a =P1+P c At 40°C, the critical gas operating pressure P1 at which the inner lining of a DN100mm non-bonded composite pipe (nylon inner lining + polyester fiber reinforcement layer + polyethylene outer protective layer) transporting CH4 gas collapses is obtained.

[0108] Example 2

[0109] The critical gas operating pressure at 60℃ for the collapse of the inner lining of a DN80mm non-bonded composite pipe (heat-resistant polyethylene inner lining + steel wire reinforcement layer + polyethylene outer protective layer) transporting CO2 gas and oil-water media is determined as follows:

[0110] (1) Gas permeability coefficient test: Film (sheet) samples with a thickness of 0.1-0.5 mm were prepared using the same raw materials as the heat-resistant polyethylene inner liner and the polyethylene outer protective layer. The test temperature was set to 60℃. Referring to GB / T 1038, the permeability coefficients of CO2 gas in the heat-resistant polyethylene and polyethylene film (sheet) samples were tested using a gas permeation meter to determine the C1 and C2.

[0111] (2) Establish the formula for calculating the interlayer permeation pressure: As shown in formula (5), test the wall thickness l1 of the inner lining of the DN100mm non-bonded composite pipe, the diameter D1 of the inner lining pipe, the wall thickness l2 of the outer protective layer, the diameter D2 of the outer protective layer, and the thickness l3 of the reinforcing layer. Under the condition that C1 and C2, R (molar gas constant, known), T (pipeline operating temperature 333K), and V (interlayer volume) can be measured or calculated, the interlayer permeation pressure P a The expression for the critical gas operating pressure P1 can be derived from equation (5):

[0112]

[0113] As can be seen from the above formula, the permeation pressure P of the non-bonded composite pipe interlayer a It is a function related to the critical gas operating pressure P1 and the operating time t.

[0114] (3) Radial collapse pressure test of heat-resistant polyethylene lined pipe: A 1500mm long non-bonded composite pipe was cut, and the heat-resistant polyethylene lined pipe was removed. A steel base pipe was then fabricated according to its outer diameter. The heat-resistant polyethylene lined pipe was inserted into the steel base pipe to form a heat-resistant polyethylene lined steel pipe test sample. An inlet was opened in the middle of the steel base pipe layer of the test sample, and a pressure sensor connection port was opened perpendicular to the inlet. According to the specifications of the DN80mm heat-resistant polyethylene lined pipe, a sealing plug was designed and installed. An intermediate connector equipped with an air inlet valve, a pressure relief valve, and a pressure gauge was connected to the sealing plug. After installing the inner sealing ring on the connected sealing plug, it was inserted into one end of the heat-resistant polyethylene lined pipe. The prepared oil-water solution was poured into the other end, and the sealing was also performed using the connected sealing plug. Then, a flange was fitted, and the flanges at both ends of the test sample were fastened together with fastening bolts. Place the entire test sample containing the liquid medium on the support base and push it into the environmental test chamber. Connect the motor's conveyor belt to the transfer connector. Start the motor to rotate the test sample, while simultaneously raising the temperature of the environmental test chamber to 60°C, and begin the environmental simulation test timing. After reaching the set test time (e.g., 200 hours), stop the motor. Keep the test sample in the environmental test chamber and maintain a constant temperature of 60°C. Connect the interlayer pressurization system and interlayer pressure monitoring system. Turn on the pressure pump to pressurize the interlayer at a rate of 0.3 MPa / s, recording the interlayer pressure changes. When the interlayer pressure reaches a certain level... Figure 3When the pressure changes as shown, stop pressurizing. The inflection point of the pressure change curve is the collapse pressure P of the heat-resistant polyethylene lining of the DN80mm non-bonded composite pipe at 60℃. c .

[0115] (4) Calculation of critical gas operating pressure for collapse of heat-resistant polyethylene liner pipe: When the interlayer pressure (P) a > Pipeline operating pressure (P1) + Collapse resistance pressure of heat-resistant polyethylene liner (P) c When P occurs, the inner liner tube collapses and fails. a =P1+P c At 60°C, the critical gas operating pressure P1 at which the inner lining of a DN80mm non-bonded composite pipe (nylon inner lining + polyester fiber reinforcement layer + polyethylene outer protective layer) transporting CH4 gas collapses is obtained.

[0116] Example 3

[0117] After 10 years of operation at 40℃ and 4MPa, determining whether the lining of a DN150mm non-bonded composite pipe (cross-linked polyethylene inner lining + polyester fiber reinforcement layer + polyethylene outer protective layer) is at risk of collapse failure.

[0118] (1) Gas permeability coefficient test: Film (sheet) samples with a thickness of 0.1-0.5 mm were prepared using the same raw materials as the cross-linked polyethylene inner liner and the polyethylene outer protective layer. The test temperature was set to 40℃. Referring to GB / T 1038, the permeability coefficients of CH4 gas in the cross-linked polyethylene and polyethylene film (sheet) samples were tested using a gas permeation meter to determine the C1 and C2.

[0119] (2) Establish the formula for calculating the interlayer permeation pressure: As shown in formula (5), test the wall thickness l1 of the inner lining of the DN100mm non-bonded composite pipe, the diameter D1 of the inner lining pipe, the wall thickness l2 of the outer protective layer, the diameter D2 of the outer protective layer, and the thickness l3 of the reinforcing layer. Under the condition that C1 and C2, R (molar gas constant, known), T (pipeline operating temperature 313K), V (interlayer volume), and operating time (10 years) can be tested or calculated, the interlayer permeation pressure P a The expression for the critical gas operating pressure P1 can be derived from equation (5):

[0120]

[0121] As can be seen from the above formula, the permeation pressure P of the non-bonded composite pipe interlayer a It is a function related to the critical gas operating pressure P1 and the operating time t.

[0122] (3) Radial collapse pressure test of cross-linked polyethylene lined pipe: A 2000mm long non-bonded composite pipe was cut, and the cross-linked polyethylene lined pipe was removed. A steel base pipe was then fabricated according to its outer diameter. The cross-linked polyethylene lined pipe was inserted into the steel base pipe to form a cross-linked polyethylene lined steel pipe test sample. An inlet was opened in the middle of the steel base pipe layer of the test sample, and a pressure sensor connection port was opened perpendicular to the inlet. According to the specifications of the DN150mm cross-linked polyethylene lined pipe, a sealing plug was designed and installed. The intermediate connector equipped with an air inlet valve, a pressure relief valve, and a pressure gauge was connected to the sealing plug. After installing the inner sealing ring on the connected sealing plug, it was inserted into one end of the cross-linked polyethylene lined pipe. The prepared oil-water solution was poured into the other end, and the sealing plug was used to seal it. Then, the flange was fitted, and the flanges at both ends of the test sample were fastened with bolts. The CH4 gas cylinder was connected to the intermediate connector, the pressure relief valve was closed, the air inlet valve was opened, and the pressure was increased to 4MPa. After closing the inlet valve, place the entire test sample containing the liquid medium and maintaining a certain internal pressure on the support base and push it into the environmental test chamber. Connect the motor's conveyor belt to the transfer connector. Start the motor to rotate the test sample while simultaneously controlling the environmental test chamber temperature at 40℃. After reaching the set test time (e.g., 240h), stop the motor and open the pressure relief valve to release the internal gas pressure of the test sample. Keep the test sample in the environmental test chamber and maintain a constant temperature of 40℃. Connect the interlayer pressurization system and the interlayer pressure monitoring system. Turn on the pressure pump to pressurize the interlayer at a rate of 0.3MPa / s, record the interlayer pressure changes, and when the interlayer pressure reaches a certain level... Figure 3 When the pressure change curve changes as shown, stop pressurizing. The inflection point of the pressure change curve is the radial collapse pressure P of the cross-linked polyethylene lined pipe under the conditions of 40℃, 4MPa operating pressure for transporting oil, water, and CH4 gas. c .

[0123] (4) Risk prediction of collapse failure of cross-linked polyethylene liner: This involves calculating and determining the interlayer pressure (P) a The collapse pressure resistance (P) of the cross-linked polyethylene liner pipe was tested and obtained. c When P a -P c If the pipeline operating pressure is 4MPa, it can be determined that after 10 years of transporting oil, water, and CH4 gas at 40℃ and 4MPa, the lining of the DN150mm non-bonded composite pipe (cross-linked polyethylene inner lining + polyester fiber reinforcement layer + polyethylene outer protective layer) is at risk of collapse failure; conversely, if P a -P c If the pipeline operating pressure is ≤4MPa, it can be determined that there is no risk of collapse failure.

[0124] Finally, it should be noted that the above-described embodiments are merely specific implementations of the present invention, used to illustrate the technical solutions of the present invention, and not to limit it. The scope of protection of the present invention is not limited thereto. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that any person skilled in the art can still modify or easily conceive of changes to the technical solutions described in the foregoing embodiments within the technical scope disclosed in the present invention, or make equivalent substitutions for some of the technical features; and these modifications, changes, or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for determining the critical gas operating pressure for the collapse of a non-bonded composite pipe lining, characterized in that, include: The volume of the interlayer between the reinforcing layer and the inner lining layer of the non-bonded composite pipe, the operating temperature of the non-bonded composite pipe, the operating time of the non-bonded composite pipe, and the composition of the gas transported by the non-bonded composite pipe are obtained. Based on the operating temperature and the composition of the transported gas, the gas permeability coefficient of the inner lining of the non-bonded composite pipe and the gas permeability coefficient of the outer protective layer of the non-bonded composite pipe were tested respectively. The interlayer volume, operating temperature, operating time, gas permeability coefficient of the inner liner, and gas permeability coefficient of the outer protective layer are input into a pre-constructed interlayer permeability pressure model between the non-bonded composite pipe reinforcement layer and the inner liner to obtain the interlayer permeability pressure between the non-bonded composite pipe reinforcement layer and the inner liner; the interlayer permeability pressure model is specifically as follows: in, ; In the formula, P a This refers to the interlayer permeability pressure; P 1 represents the critical gas operating pressure; P 2 represents atmospheric pressure; R represents the molar gas constant; T Operating temperature; V For the volume of the interlayer; t Runtime; C 1 represents the gas permeability coefficient of the inner lining layer; C 2 represents the gas permeability coefficient of the outer protective layer; D 1 represents the diameter of the inner lining layer; D 2 represents the diameter of the outer protective layer; l 1 represents the wall thickness of the inner lining layer; l 2 represents the thickness of the outer protective layer; Determine the radial collapse pressure of the non-bonded composite pipe liner; The interlayer permeation pressure and the radial collapse pressure are input into a pre-constructed critical collapse failure criterion model to obtain the critical gas operating pressure for the collapse of the non-bonded composite pipe lining. The critical collapse failure criterion model is as follows: P a = P 1 + P c In the formula, P c This refers to the radial collapse pressure of the inner lining of a non-bonded composite pipe.

2. The method for determining the critical gas operating pressure for the collapse of a non-bonded composite pipe lining according to claim 1, characterized in that, The step of testing the gas permeability coefficient of the inner lining of the non-bonded composite pipe and the gas permeability coefficient of the outer protective layer of the non-bonded composite pipe based on the operating temperature and the composition of the transported gas specifically includes: A first thermoplastic film sample was prepared using the same raw material as the inner lining of the non-bonded composite pipe, and a second thermoplastic film sample was prepared using the same raw material as the outer protective layer of the non-bonded composite pipe. The gas permeation test temperature is set to the operating temperature. A gas permeameter is used to test the gas permeation coefficient of the transported gas component in the first thermoplastic film sample, which is the gas permeation coefficient of the inner lining of the non-adhesive composite pipe. The gas permeation coefficient of the transported gas component in the second thermoplastic film sample is also tested, which is the gas permeation coefficient of the outer protective layer of the non-adhesive composite pipe.

3. The method for determining the critical gas operating pressure for the collapse of a non-bonded composite pipe lining according to claim 2, characterized in that, The preparation process of the first thermoplastic film sample is the same as that of the preparation process of the non-adhesive composite pipe liner. The preparation process of the second thermoplastic film sample is the same as that of the preparation process of the outer protective layer of the non-adhesive composite pipe.

4. The method for determining the critical gas operating pressure for the collapse of a non-bonded composite pipe lining according to claim 1, characterized in that, Determining the radial collapse pressure of the non-bonded composite pipe liner specifically includes: Environmental simulation tests were conducted on the test samples of the non-bonded composite pipe. Radial pressure tests were conducted on the inner lining of the unbonded composite pipe test samples, and the changes in interlayer pressure between the reinforcing layer and the inner lining of the unbonded composite pipe samples were recorded. Based on the change in interlayer pressure between the reinforcing layer and the inner lining layer of the unbonded composite pipe sample, plot the curve of the interlayer pressure change between the reinforcing layer and the inner lining layer of the unbonded composite pipe sample. The radial collapse pressure of the inner lining of the non-bonded composite pipe is obtained from the interlayer pressure variation curve.

5. The method for determining the critical gas operating pressure for the collapse of a non-bonded composite pipe lining according to claim 4, characterized in that, When performing radial pressure tests on the inner lining of the non-bonded composite pipe test sample, the pressure rate is controlled between 0.1 MPa / s and 0.5 MPa / s.

6. The method for determining the critical gas operating pressure for the collapse of a non-bonded composite pipe lining according to claim 1, characterized in that, The formula for calculating the interlayer volume between the reinforcing layer and the inner lining layer of the non-bonded composite pipe is as follows: Interlayer volume = outer surface area of ​​inner lining layer × thickness of reinforcing layer × (1 - volume fraction of reinforcing layer); The volume fraction of the reinforcing layer was obtained by Archimedes' method of water displacement.

7. The method for determining the critical gas operating pressure for the collapse of a non-bonded composite pipe lining according to claim 1, characterized in that, When there are fluctuations or negative pressure in the operating pressure of the non-bonded composite pipe, the radial collapse pressure should be corrected with a correction factor of 0.5 to 0.8.

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