Method for testing salt crystallization resistance of pipe material and dynamic experimental device

Abstract

The application discloses a method for testing salt crystallization resistance of pipe and a dynamic experimental device, wherein the method takes an uncoated base pipe stub and a coated pipe stub to be evaluated as synchronous control samples, and respectively vertically clamps the two to form a flow channel with liquid inlet at the bottom and liquid outlet at the top; the initial flow difference of the two branches is adjusted to a preset balance range in the same batch of salt-containing test medium, and then the medium is lowered to a target temperature under a preset temperature reduction program, and temperature, flow, pressure difference and conductivity data are collected online, and at least two parameters are used to form test endpoint judgment value; after the test, the same conditions are used for cleaning, drying and weighing, the salt crystallization adhesion per unit inner surface area is measured, and the salt crystallization resistance is evaluated. The device comprises a solution pool, a programmable temperature control unit, a circulating pump, a shunt assembly, two groups of vertical test pipe segment support assemblies, a sensor assembly and an acquisition control module. The application improves the consistency, repeatability and quantification of the salt crystallization resistance comparison and evaluation of the base pipe and the coated pipe.

Description

Technical Field

[0001] This invention relates to the field of performance evaluation technology for pipes and pipe inner wall coatings, and particularly to a method and dynamic experimental apparatus for testing the salt crystallization resistance of pipes. Background Technology

[0002] In oil and gas extraction, high-salinity water injection, brine transportation, and saline wastewater transportation, the inner wall of the pipe is in long-term contact with fluids containing soluble salts such as NaCl, CaCl2, MgCl2, Na2SO4, and NaHCO3. Affected by temperature drops, pressure fluctuations, flow rate changes, restarts after shutdowns, and differences in local wall conditions, the salts easily reach saturation or supersaturation and precipitate, adhere, and grow on the inner wall of the pipe.

[0003] In engineering projects, low surface energy coatings, anti-corrosion and anti-scaling coatings, or composite coatings are commonly used to reduce the risk of salt crystallization. Evaluating the effectiveness of such coatings cannot rely solely on the weighing results after static immersion; it is also necessary to consider factors such as flow shear, temperature-induced crystallization, pipe section pressure differential changes, and flow rate attenuation.

[0004] Chinese invention patent application CN104515836A discloses a method and dynamic experimental apparatus for testing the anti-scaling and anti-waxing performance of pipe materials. This apparatus includes a media tank, a corrosion-resistant centrifugal pump, a delivery pipeline, a flow control valve, a digital flow meter, a temperature control system, and a test pipe section. A circulating pump drives the liquid test medium through the test pipe section. After a certain test cycle, the anti-scaling and anti-waxing performance of the pipe material is evaluated based on changes in the mass, wall thickness, and inner surface morphology of the test pipe section. While this type of apparatus solves the fundamental problem of media circulation simulation, it still has the following shortcomings when used to compare and evaluate the salt crystallization resistance of base pipes and coated pipes: 1. Although multiple test sections can be set up, there is a lack of adjustment methods to keep the branch flow rates of two test sections consistent. The actual flow conditions experienced by the two samples are not strictly the same, and the contribution of flow condition differences is mixed into the comparison results. 2. The test mainly uses isothermal circulation, while salt crystallization is a highly temperature-sensitive process. Salt scale precipitation in the field is mainly induced by temperature decreases. This type of device lacks a temperature program for actively inducing crystallization through controlled cooling, making it difficult to reproduce the driving process of in-situ crystallization. 3. The test endpoint relies on a preset time or manual observation. The cutoff states of different batches of tests are inconsistent, resulting in poor data repeatability. 4. There is a lack of a unified quantitative evaluation relationship between the post-test weighing results and the flow rate, pressure difference, and conductivity data during operation. Online data is not included in the evaluation system.

[0005] In view of this, the applicant is considering designing a method and dynamic experimental device for testing the salt crystallization resistance of pipes with higher consistency, repeatability and quantification of test results. Summary of the Invention

[0006] In view of the shortcomings of the prior art, the technical problem to be solved by the present invention is: How to design a method and dynamic experimental device for testing the salt crystallization resistance of pipes with higher consistency, repeatability and quantification of test results.

[0007] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: A method for testing the salt crystallization resistance of pipes, characterized by comprising the following steps: S1. Short-connect the uncoated base pipe and the coated pipe to be evaluated, and clamp them side by side to form two test pipe sections. Liquid enters at one end and exits at the other end of both test pipe sections. S2. Ensure that the same batch of salt-containing test media is in any one of the following states: saturated, near-saturated, or supersaturated at a preset initial temperature. S3. The salt-containing test medium is circulated through the two test pipe sections in two branches, and the initial flow difference between the two branches is adjusted to a preset equilibrium range. S4. Under circulating flow, the temperature is reduced to the target temperature according to the preset cooling program. The temperature, flow rate, pressure difference, and conductivity of each test tube section are collected online. During the cooling process, the rate of decrease of the collected conductivity is calculated in real time. When the rate of decrease exceeds the preset upper threshold, the cooling is paused or the cooling rate is switched to the preset low speed. When the rate of decrease falls below the preset lower threshold, the preset cooling program is resumed until the temperature reaches the target temperature. During the cooling process, at least one switching operation is also performed to interchange the flow paths of the two branches so that the cumulative flow time of each test tube section on the two branches is the same. The switching time is recorded. S5. Use at least two of the following as endpoint values: test duration, flow rate attenuation rate, pressure difference rise rate, and conductivity change rate. Stop the circulation flow once the endpoint value is reached. S6. Determine the amount of salt crystallization adhering per unit internal surface area of ​​each of the two test pipe sections under the same post-treatment conditions. S7. After pairing and calculating the segmented data before and after the transposition, compare and evaluate the salt crystallization resistance of the two test pipe sections.

[0008] Furthermore, the uncoated base pipe short joint and the coated pipe short joint to be evaluated have the same nominal length and nominal inner diameter, and both were cleaned, dried and weighed before the test.

[0009] Furthermore, in step S3, the initial flow difference between the two branches is controlled within 10% of the initial flow of the larger branch, and the initial flow rates Qb0 and Qt0, as well as the initial pressure differences ΔPb0 and ΔPt0, are recorded for the branches corresponding to the uncoated base pipe short circuit and the coated pipe to be evaluated short circuit, respectively.

[0010] Furthermore, in step S4, the preset initial temperature is 60℃ to 90℃, and after reaching the preset initial temperature, it is kept at that temperature for 5 minutes to 60 minutes before cooling begins; the target temperature is 15℃ to 30℃, and the preset cooling program is linear cooling at a cooling rate of 0.5℃ / h to 10℃ / h, or cooling according to a preset segmented cooling curve.

[0011] Furthermore, in step S2, the ionic composition, pH, and conductivity of the saline test medium are recorded or adjusted; the saline test medium is oil well produced fluid that has undergone deoiling and degassing treatment, or an artificially prepared salt solution containing one or more of NaCl, CaCl2, MgCl2, Na2SO4, and NaHCO3.

[0012] Further, in step S5, the flow rate attenuation rate includes the flow rate attenuation rate of the uncoated base pipe short circuit Fb=(Qb0-Qbe) / Qb0 and the flow rate attenuation rate of the coated pipe to be evaluated short circuit Ft=(Qt0-Qte) / Qt0, and the differential pressure rise rate includes the differential pressure rise rate of the uncoated base pipe short circuit Pb=(ΔPbe-ΔPb0) / ΔPb0 and the differential pressure rise rate of the coated pipe to be evaluated short circuit Pt=(ΔPte-ΔPt0) / ΔPt0, where Qbe and Qte are the flow rates of the corresponding branches of the uncoated base pipe short circuit and the coated pipe to be evaluated short circuit at the end of the test, respectively, and ΔPbe and ΔPte are the differential pressures of the uncoated base pipe short circuit and the coated pipe to be evaluated short circuit at the end of the test, respectively.

[0013] Furthermore, in step S6, the amount of salt crystals adhering per unit internal surface area is calculated as M=(m1-m0) / S, where m0 is the dry mass of the test tube section before the test, m1 is the mass of the test tube section after the test under the same cleaning and drying conditions, and S is the internal surface area of ​​the test tube section. In step S6, each test pipe section is subjected to standardized detachment treatment under the same detachment treatment conditions, and the crystallization adhesion coefficient is calculated according to K=(m2-m0) / (m1-m0), where m2 is the mass of the test pipe section after standardized detachment treatment and drying. In step S7, the salt crystallization resistance rate of the short-circuited coated pipe to be evaluated relative to the short-circuited uncoated base pipe is calculated as η=(Mb-Mt) / Mb×100%, where Mb and Mt are the amount of salt crystallization adhesion per unit internal surface area of ​​the short-circuited uncoated base pipe and the short-circuited coated pipe to be evaluated, respectively.

[0014] A dynamic experimental apparatus for implementing the above method is characterized in that it includes a solution tank, a programmable temperature control unit, a circulating pump, a main pipeline, a flow splitting assembly, a first vertical test tube section support assembly, a second vertical test tube section support assembly, a return pipeline, a sensor assembly, and a data acquisition and control module. The solution tank is used to contain the same batch of saline test medium; the programmable temperature control unit is used to raise the saline test medium to a preset initial temperature, maintain its temperature, and lower it to the target temperature according to a preset cooling program; the inlet of the circulating pump is connected to the solution tank, and the outlet is connected to the diversion assembly via a main pipeline; the diversion assembly is connected to the lower inlet of the first vertical test pipe section support assembly and the second vertical test pipe section support assembly respectively; the upper outlet of the first vertical test pipe section support assembly and the second vertical test pipe section support assembly is connected to the solution tank via a return pipeline; the sensor assembly is used to collect the temperature, flow rate, and pressure difference corresponding to each test pipe section, as well as the conductivity of the saline test medium; the acquisition and control module is configured to perform branch flow balancing, controlled cooling, online data acquisition, and test endpoint determination; during the controlled cooling process, the acquisition... The control module calculates the rate of decrease of the collected conductivity in real time. When the rate of decrease exceeds a preset upper threshold, cooling is paused or the cooling rate is switched to a preset low speed. When the rate of decrease falls below a preset lower threshold, the preset cooling program is resumed until the salt-containing test medium drops to the target temperature. A reversing valve group is also provided between the flow splitting component and the first vertical test pipe section support component and the second vertical test pipe section support component. The reversing valve group has a straight-through state and a cross state: in the straight-through state, the first branch connects to the first vertical test pipe section support component and the second branch connects to the second vertical test pipe section support component; in the cross state, the flow paths of the two branches are interchanged. The acquisition control module is also configured to perform at least one reversal operation through the reversing valve group and record the reversal time, and to pair and calculate the segmented data before and after the reversal.

[0015] Furthermore, both the first and second vertical test pipe section support assemblies include a support frame, an upper sealing joint, a lower sealing joint, and a clamping component. The upper and lower sealing joints are respectively sealed to the threaded or end connection structures at both ends of the test pipe section to form a vertical flow channel with liquid inlet at the bottom and liquid outlet at the top. The flow splitting assembly includes a flow splitter, a first branch flow regulating valve, a second branch flow regulating valve, a first branch flow sensor, and a second branch flow sensor. The acquisition and control module adjusts the first and second branch flow regulating valves according to the detection values ​​of the first and second branch flow sensors to ensure that the initial flow difference between the two branches is within a preset balance range.

[0016] Furthermore, the sensor assembly includes a temperature sensor and a flow sensor disposed on the inlet side and / or outlet side of each test tube segment, a differential pressure sensor bridging the inlet and outlet of each test tube segment, and a conductivity sensor disposed on the solution tank or main pipeline.

[0017] Compared with existing technologies, the beneficial technical effects of the method and dynamic experimental device for testing the salt crystallization resistance of pipes in this invention are: (1) The present invention places the uncoated base pipe short section and the coated pipe short section to be evaluated under the same batch of salt-containing test medium and the same controlled cooling program for synchronous testing, and limits both test pipe sections to adopt vertical bottom inlet and top outlet flow channels, which can reduce the influence of medium batch, cooling process and installation posture differences on the evaluation results, and at the same time simulate the flow shear, gravity direction and temperature-induced salt crystallization process in the vertical pipe section.

[0018] (2) This invention enables the simultaneous recording of salt crystallization adhesion, blockage trend and medium concentration change by balancing branch flow and collecting temperature, flow rate, pressure difference and conductivity data online; at least two of the following are used to form the endpoint judgment value: test duration, flow rate decay rate, pressure difference rise rate and conductivity change rate, which reduces the repeatability deviation caused by stopping the test by manual observation alone.

[0019] (3) This invention combines standardized cleaning and drying, standardized peeling treatment with indicators such as salt crystal adhesion amount per unit internal surface area, crystal adhesion coefficient, salt crystallization resistance rate and flow attenuation rate, which facilitates quantitative comparison of the salt crystallization resistance of the coated pipe relative to the base pipe. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the system structure of the dynamic experimental device of the present invention; Figure 2 This is a schematic diagram of the vertical double test tube support module in the dynamic experimental device of the present invention; Figure 3 This is a flowchart of the method for testing the salt crystallization resistance of pipes according to the present invention; Figure 4 This is a diagram showing the relationship between data acquisition and evaluation indicators in the method of this invention; Figure 5 This is a schematic diagram of the wall temperature regulating sleeve in the dynamic experimental device of the present invention; Figure 6 This is a logic block diagram of the adaptive cooling control of crystallization rate in the method of the present invention; Figure 7 This is a schematic diagram of the differential pressure response under intermittent start-stop conditions in the method of the present invention; Figure 8 This is a schematic diagram of the dual-branch cross-positioning pipeline in the dynamic experimental device of the present invention; Figure 9 This is a physical schematic diagram of one embodiment of the dynamic experimental device of the present invention.

[0021] Explanation of reference numerals in the attached figures: 1. Solution tank; 2. Stirring / heating module; 3. Circulating pump; 4. Main pipeline; 5. Flow divider; 6. First test section; 7. Second test section; 8. Support frame; 9. Valve assembly; 91. First branch flow regulating valve; 92. Second branch flow regulating valve; 10. Flow sensor; 11. Temperature sensor; 12. Differential pressure sensor; 13. Conductivity sensor; 14. Data acquisition and control module; 15. Return pipeline; 16. Cooling module; 17. Upper sealing joint; 18. Lower sealing joint; 19. Clamping component; 20. Wall temperature regulating sleeve; 21. Wall temperature sensor; 22. Reversing valve assembly; 23. Transparent observation section; 24. Upper crossbeam; 25. Lower crossbeam. Detailed Implementation

[0022] The present invention will be further described below with reference to the accompanying drawings and embodiments. The following embodiments are used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention.

[0023] Example 1: like Figure 1 As shown, the dynamic experimental apparatus includes a solution tank 1, a stirring / heating module 2, a circulating pump 3, a main pipeline 4, a flow divider 5, a first test pipe section 6, a second test pipe section 7, a support frame 8, a valve assembly 9, a flow sensor 10, a temperature sensor 11, a differential pressure sensor 12, a conductivity sensor 13, a data acquisition and control module 14, a return pipeline 15, and a cooling module 16. The flow divider 5 and the valve assembly 9 together constitute a flow divider component. The valve assembly 9 includes a first branch flow regulating valve 91 and a second branch flow regulating valve 92. Flow sensors 10, which serve as branch flow sensors, are also installed on each of the two branches.

[0024] Solution tank 1 is used to contain the same batch of salt-containing test media. Stirring / heating module 2 and cooling module 16 constitute a programmable temperature control unit, which is used to raise the salt-containing test media to a preset initial temperature, maintain the temperature for stability, and lower it to the target temperature according to linear cooling, segmented cooling, or the on-site temperature curve.

[0025] The circulating pump 3 transports the saline test medium from the solution tank 1 to the main pipeline 4, and then distributes it to the first test section 6 and the second test section 7 via the distributor 5. The circulating pump 3 can be a submersible pump installed inside the solution tank 1 or a pipeline pump installed outside the solution tank 1; when using a submersible pump, the inlet of the circulating pump 3 is directly immersed in the saline test medium, and its outlet is led out of the solution tank 1 via the main pipeline 4. The acquisition and control module 14 adjusts the first branch flow regulating valve 91 and the second branch flow regulating valve 92 to balance the flow based on the detection values ​​of the two branch flow sensors 10, so that the initial flow difference between the two branches is within a preset balance range.

[0026] Temperature sensor 11 is installed on the inlet and outlet sides of each test pipe section, flow sensor 10 is installed on each branch pipe, differential pressure sensor 12 is connected between the inlet and outlet of each test pipe section, and conductivity sensor 13 is installed on the solution tank 1 or the main pipe 4. The data acquisition and control module 14 records the flow-time, temperature-time, differential pressure-time, and conductivity-time curves, and determines whether the test endpoint has been reached based on at least two of the following: flow rate decay rate, differential pressure rise rate, conductivity change rate, and test duration.

[0027] Example 2: like Figure 2 As shown, the support frame 8 includes columns and upper and lower crossbeams 24 and 25 spaced apart along the height direction. Positioning holes for the test pipe sections to pass through are provided side-by-side on the upper and lower crossbeams. The first test pipe section 6 and the second test pipe section 7 are vertically inserted side-by-side through the positioning holes in the upper and lower crossbeams and locked in place by clamping members 19. The two pipe positions on the support frame 8 respectively constitute the first vertical test pipe section support assembly and the second vertical test pipe section support assembly; that is, the two sets of support assemblies share the same support frame 8, or they can each use independent support frames. The first test pipe section 6 can be a short-connected uncoated base pipe, and the second test pipe section 7 can be a short-connected coated pipe. The length of the two test pipe sections can be from 0.5m to 1.5m, preferably 1m; the inner diameter, wall thickness, and end connection form of the two test pipe sections are preferably the same or similar.

[0028] The lower end of each test tube section is connected to the inlet pipe via a lower sealing joint 18, and the upper end is connected to the return pipe 15 via an upper sealing joint 17. The upper sealing joint 17 and the lower sealing joint 18 are respectively sealed to the threaded or end connection structures at both ends of the test tube section. The upper sealing joint 17 and the lower sealing joint 18 are located above the upper crossbeam and below the lower crossbeam, respectively. The salt-containing test medium enters from the bottom of the test tube section and flows out from the top, forming a vertical flow channel with the two test tube sections in the same direction that can be compared synchronously.

[0029] The clamping component 19 can be a locking bolt or a locking flange located at the positioning hole of the crossbeam; as a variation, the clamping component 19 can also adopt a split clamp structure, or a structure in which a V-shaped positioning block cooperates with a pressure plate, to facilitate the quick loading, unloading and replacement of the test tube section. A transparent observation section 23 can also be provided on the return pipe 15 (see...). Figure 1 (Illustrated in the middle) Transparent observation section 23 is a transparent pressure-resistant pipe section used to observe whether the reflux medium carries detached crystals, and to help interpret abrupt events in the flow rate or differential pressure curve.

[0030] Example 3: A method for testing the resistance of pipes to salt crystallization includes the following steps: S1. Sample preparation and synchronous clamping. Cut short sections of uncoated base pipe and coated pipe to be evaluated with the same nominal length and nominal inner diameter. After cleaning the inner wall, dry to constant weight. Record the mass m0, inner diameter and length before the test. Record the initial morphology of the inner surface if necessary. Then, install them in the first vertical test pipe section support assembly and the second vertical test pipe section support assembly respectively, so that both test pipe sections form vertical flow channels with liquid inlet at the bottom and liquid outlet at the top.

[0031] S2. Salt Solution Preparation. Add the same batch of salt-containing test medium to the solution tank, and record or adjust the ionic composition, pH, and conductivity. The salt-containing test medium can be oil well produced fluid that has undergone deoiling and degassing treatment, or it can be an artificially prepared salt solution containing one or more of NaCl, CaCl2, MgCl2, Na2SO4, and NaHCO3. The deviation between the conductivity of the artificially prepared salt solution and the set conductivity at the preset initial temperature can be controlled within 10%. After adding the medium, it can be pre-circulated at low speed in the bypass circuit and filtered to remove suspended particles and insoluble impurities carried in the medium. Suspended particles are the nuclei of heterogeneous nucleation. If they are not removed in advance, heterogeneous nucleation in the medium will consume supersaturation and produce random deposition, interfering with the comparison of nucleation and adhesion on the walls of the two test pipe sections. After pre-circulation and impurity removal, the crystallization behavior during the test is more concentrated on the pipe wall surface, and the repeatability of the comparison results is improved.

[0032] S3. Flow balance. Start the circulating pump and adjust the valve group to control the initial flow difference between the two branches within 10% of the initial flow of the larger branch, and further control it within 5%. Record Qb0, Qt0, ΔPb0 and ΔPt0.

[0033] S4. Preheating and Controlled Cooling. The saline test medium is heated to 60°C to 90°C and held for 5 to 60 minutes to stabilize the temperature of the solution tank, pipelines, and test section. Subsequently, the saline test medium is cooled to 15°C to 30°C at a rate of 0.5°C / h to 10°C / h or according to a segmented cooling curve. During the cooling process, circulation is maintained, and temperature, flow rate, pressure difference, and conductivity data are collected. Depending on the experimental requirements, one or more of the following methods described in Examples 5 to 8 can be superimposed in this step: wall subcooling control, adaptive cooling control, intermittent start-stop operation, and branch repositioning operation.

[0034] S5. Endpoint Determination. At least two of the following endpoints are used as endpoint criteria: test duration, flow rate attenuation, differential pressure rise rate, and conductivity change rate. The cyclic test is stopped when all selected endpoint criteria are met. For example, the cyclic test is stopped when the preset test duration is reached and at least one of the flow rate attenuation, differential pressure rise rate, or conductivity change rate reaches a preset threshold or tends to stabilize within a preset time.

[0035] S6. Standardized Post-treatment. Two test tube sections are taken out and treated with the same cleaning volume, cleaning time, drying temperature, and drying time, and weighed to obtain m1. Then, the same brushing material, brushing frequency, and pressure range are used for detachment treatment, and the tubes are dried and weighed to obtain m2. The detachment treatment can be completed using a constant-pressure brushing fixture: the brush head applies constant pressure against the inner wall of the tube section via a spring or counterweight, and brushes back and forth with a fixed stroke and a fixed number of strokes. Manual brushing involves varying brushing force, which directly affects the measured value of m2, and thus the comparability of the adhesion coefficient K. The constant-pressure brushing fixture fixes the brushing pressure, stroke, and number of strokes as device parameters, making the determination of K independent of human experience, and ensuring comparability of results between different batches and different operators.

[0036] S7. Calculation and Evaluation of Indicators. Calculate the salt crystallization adhesion amount M per unit internal surface area, the strong adhesion coefficient K, the salt crystallization resistance rate η, and the flow rate attenuation rate F. Combine the morphological observation results to evaluate the salt crystallization resistance performance of the short-circuit pipe to be evaluated. If necessary, check the coating integrity of the short-circuit pipe to be evaluated, observe whether there are scratches, bubbles, peeling, or corrosion points on the coating surface, and use the cross-cut adhesion test to evaluate the stability of the coating in the salt crystallization environment.

[0037] Regarding evaluation indicators: The amount of salt crystals adhering to a unit internal surface area, M, is calculated as M=(m1-m0) / S, where m0 is the dry mass of the test section before the test, m1 is the mass of the test section after the test following pre-set cleaning and drying, and S is the internal surface area of ​​the test section.

[0038] The adhesion coefficient K is calculated as K=(m2-m0) / (m1-m0), where m2 is the mass of the test pipe section after standardized peeling treatment and drying. K is used to characterize the degree of adhesion of the crystalline layer to the inner wall of the pipe.

[0039] The salt crystallization resistance rate η is calculated as η=(Mb-Mt) / Mb×100%, where Mb is the amount of salt crystallization adhesion per unit inner surface area of ​​the uncoated base pipe short circuit, and Mt is the amount of salt crystallization adhesion per unit inner surface area of ​​the coated pipe short circuit to be evaluated.

[0040] The flow rate attenuation rate F is calculated as F=(Q0-Qe) / Q0, where Q0 is the initial stable flow rate of the test and Qe is the final flow rate of the test. For simultaneous dual-pipe tests, the flow rate attenuation rate Fb of the uncoated base pipe and the flow rate attenuation rate Ft of the coated pipe to be evaluated can be calculated separately.

[0041] The comprehensive salt crystallization resistance evaluation index I can be obtained by weighting the changes in η, K, and F. The weights can be set according to the application scenario; for example, in scenarios where the risk of clogging is a concern, the weight of the change in F is increased, and in scenarios where the strength of crystal adhesion is a concern, the weight of the change in K is increased.

[0042] Example 4: In a typical implementation, the first test section is a 1m long N80 base pipe short-connection, and the second test section is a 1m long JY2200Q coated tubing short-connection. Both are vertically installed on support frames, and the same batch of deoiled and degassed downhole produced fluid is used as the salinity test medium.

[0043] The saline test medium is heated to 80°C and held at that temperature for 10 to 30 minutes, ensuring the initial flow difference between the two branches is controlled within 5%. The temperature is then reduced to 20°C under circulating flow conditions. The test flow rate can be set to at least one of 800 L / h, 1600 L / h, and 2400 L / h. Temperature, flow rate, pressure difference, and conductivity curves for each pipe section are recorded during the test.

[0044] After the test, two test pipe sections were treated with the same cleaning volume, drying conditions, and light brushing conditions. M, K, F, and η were calculated, and the salt crystallization resistance of the coated tubing relative to the base pipe was determined based on the inner surface crystal morphology. In another embodiment, the initial temperature was set to 60℃, the target temperature to 20℃, and the cooling time to 10-14 hours; the test medium was an artificial high-mineralization salt solution containing NaCl, CaCl2, MgCl2, and Na2SO4. These parameters can be adjusted according to the composition of the oilfield produced fluid, wellbore temperature, or pipeline operating conditions.

[0045] Example 5: like Figure 5 As shown, the outer wall of each test tube section is covered with a wall temperature regulating sleeve 20. The wall temperature regulating sleeve 20 is an annular jacket structure and is installed on the outer wall section of the tube section between the upper and lower crossbeams of the support frame 8. Its inner cavity is connected to the heat exchange circuit, and the temperature and flow rate of the heat exchange medium in the heat exchange circuit are regulated by the acquisition and control module 14. A wall temperature sensor 21 is also attached to the outer wall of the test tube section. The wall temperature regulating sleeves 20 of the two test tube sections adopt the same structure and are supplied in parallel by the same heat exchange circuit to ensure that the thermal boundary conditions of the two sample walls are consistent.

[0046] During the experiment, the acquisition and control module 14 adjusts the heat exchange capacity of the heat exchange circuit according to the difference between the medium temperature and the value detected by the wall temperature sensor 21, so that the subcooling of the wall surface is maintained within a preset subcooling range, such as 2°C to 15°C. In other words, while the medium as a whole is cooled according to the preset cooling program, the pipe wall surface is additionally maintained with a controlled low temperature bias.

[0047] In field wellbores and surface pipelines, the pipe wall temperature is usually lower than the fluid temperature inside the pipe due to heat dissipation to the surrounding rock or environment. Supercooling of the pipe wall is a key driving force for preferential salt crystallization on the pipe wall. Simply cooling the entire medium cannot reproduce this radial temperature difference. Through controlled supercooling, crystallization preferentially occurs on the pipe wall surface rather than the bulk medium. The resulting crystallized layer morphology more closely resembles the scale samples from the field, and the crystallization induction time is shortened, thus reducing the test cycle. In a modified embodiment, the wall temperature regulating sleeve 20 can also be a semiconductor cooling chip assembly attached to the outer wall of the pipe section, set according to a preset supercooling degree gradient to achieve a series of comparative tests under different supercooling degree gradients.

[0048] Example 6: like Figure 6 As shown, the acquisition and control module 14 calculates the rate of decrease in conductivity data in real time during the controlled cooling process. When salts precipitate in a salt-containing medium, the ion concentration in the solution decreases, and the conductivity decreases accordingly. Therefore, the rate of decrease in conductivity can characterize the crystallization rate of the bulk medium. The entire control logic is as follows: When the rate of decrease in conductivity exceeds a preset upper threshold, it is determined that rapid crystallization is occurring in the bulk medium. At this point, cooling is paused or the cooling rate is switched to a preset low speed to allow the system to approach quasi-equilibrium. When the rate of decrease in conductivity falls below a preset lower threshold, the original cooling program is resumed until the target temperature is reached. The upper and lower thresholds can be set as a percentage of the initial conductivity of the medium. For example, a decrease of 2% of the initial conductivity per hour can be used as the upper threshold trigger condition (the specific value can be calibrated by the inventor based on the medium system).

[0049] When using a fixed cooling rate, if the rate is too fast, explosive crystallization will occur in the bulk medium, and the resulting suspended crystals will deposit in both pipe sections, masking the true difference in nucleation and adhesion between the coating and the base pipe on the wall surface. If the rate is too slow, the test cycle will be unnecessarily prolonged. Adaptive cooling constrains the crystallization rate within the range dominated by wall adhesion, improving the resolution and repeatability of comparative evaluation while also considering test efficiency. In a modified embodiment, the crystallization rate can also be determined by combining the detection values ​​from a turbidity sensor.

[0050] Example 7: like Figure 7 As shown, at least one intermittent start-stop operation is inserted during the controlled cooling phase: the circulation pump 3 is stopped and left to stand for a preset standing time, which can be 0.5h to 4h. During the standing time, the temperature program can continue to be executed or the temperature can be kept constant. Then the circulation pump 3 is restarted, and the peak pressure difference and pressure difference recovery time of each test tube segment during the restart process are collected at a preset sampling frequency.

[0051] During the settling period, the crystals already attached to the pipe wall continue to grow, bridge, and solidify under conditions of no flow shear. Upon restart, the fluid impacts the solidified crystalline layer, causing a momentary peak in the pressure differential. The peak value reflects the degree of blockage of the flow channel by the crystalline layer, while the pressure differential recovery time reflects the crystalline layer's resistance to erosion. Comparing the differences in peak restart pressure differential and recovery time between the coated pipe and the base pipe allows for a quantitative evaluation of the coating's ability to inhibit crystal solidification. This operating condition directly corresponds to a shutdown and restart scenario in the field, compensating for the inability of continuous cycle tests to cover the settling and solidification process.

[0052] Example 8: like Figure 8 As shown, a reversing valve assembly 22 is installed between the distributor 5 and the two sets of support components. The reversing valve assembly 22 can be arranged near the location where the main inlet pipe branches into two branches. The reversing valve assembly 22 has a straight-through state and a cross-flow state: in the straight-through state, the first branch connects to the first test pipe section 6, and the second branch connects to the second test pipe section 7; in the cross-flow state, the flow paths of the two branches are interchanged.

[0053] A transposition operation is performed approximately halfway through the total test duration to ensure that the cumulative flow time of each test pipe segment is the same on both branches; alternatively, multiple transpositions can be performed at equal time intervals. The transposition operation is completed within a few seconds by the reversing valve assembly 22, and the disturbance to the flow field is negligible. The transposition time is recorded in the data sequence by the acquisition and control module 14, and the segmented data before and after the transposition are paired and calculated during data processing.

[0054] The pipe resistance, valve characteristics, and sensor zero drift of the two branches cannot be absolutely identical. Over long-term comparative testing, these differences will accumulate into a systematic bias, directly superimposed on the actual differences between the coating and the base pipe. The transposition operation makes this systematic bias symmetrically distributed between the two test pipe sections, and it is canceled out after pairing and calculation. In other words, even if there are unavoidable hardware differences between the two branches, the comparison results still only reflect the differences in the salt crystallization resistance of the samples themselves.

[0055] Example 9: During prolonged experiments, as salts continuously precipitate and adhere, the salt concentration in the solution pool gradually decreases, leading to a decline in the crystallization driving force. This causes the adhesion rate in the later stages of the experiment to no longer reflect the true operating conditions, compressing the effective window for comparing the two samples. To address this, the dynamic experimental setup can also include a replenishment unit. This unit comprises a concentrated salt solution storage tank, a metering pump, and a replenishment pipeline connected to the solution pool. The acquisition and control module, based on the decrease in conductivity sensor 13 relative to the initial set value, controls the metering pump to quantitatively replenish the solution pool with concentrated salt solution, maintaining the medium conductivity near the set value and thus ensuring a nearly constant crystallization driving force throughout the experiment. The replenishment volume and timing are recorded by the acquisition and control module and factored into the medium mass balance.

[0056] Based on this, the acquisition and control module can also pre-store the temperature-saturation conductivity calibration curve of the salt-containing test medium used. The calibration curve is obtained by pre-measuring the saturation conductivity of the batch of medium at different temperatures. During the test, the acquisition and control module calculates the relative saturation index of the medium in real time based on the current medium temperature and current conductivity, which is the ratio of the current conductivity to the saturation conductivity at that temperature. The relative saturation index is used as the process control variable to replace or supplement the simple temperature control variable: controlled cooling, adaptive cooling, and endpoint judgment can all be executed based on the relative saturation index. Since the relative saturation index eliminates the influence of batch differences and temperature point differences, the test results of different batches of medium and different temperature programs can be compared under the same saturation coordinate, improving the transferability of test conditions and the comparability of results.

[0057] Example 10: In addition to flow rate and differential pressure, wall temperature drift can be used for non-destructive online monitoring of the adhesion process. The thermal conductivity of the salt crystallization layer is significantly lower than that of the metal pipe wall. As the crystallization layer thickens on the inner wall of the pipe, the thermal resistance between the pipe wall and the medium increases. Under constant heat exchange conditions maintained by the wall temperature regulating sleeve 20, the outer wall temperature detected by the wall temperature sensor 21 will gradually drift as the crystallization layer thickens. The acquisition and control module records the difference in the outer wall temperature drift curves of the two test pipe sections as an online indirect indication of the difference in adhesion thickness between the two samples. This monitoring channel is independent of the flow rate and differential pressure channels. Cross-verification of the three can identify sensor malfunctions or abnormal operating conditions during the test, avoiding the invalidation of the entire test.

[0058] A removable filter can also be installed on the return pipe 15. The filter screen is weighed before the test. During the test, crystal particles that fall off with the flow of the medium are trapped by the filter screen. After the test, the filter screen is removed, dried, and weighed to obtain the amount of crystals that fall off with the flow. Based on this, a mass balance check can be established for the total amount of medium precipitation: the amount of salt precipitated in the medium is equal to the sum of the amount of salt adhering to the two test pipe sections, the amount trapped by the filter screen, and the amount of salt deposited at the bottom of the solution pool. The total amount of medium precipitation can be calculated from the change in conductivity and the replenishment record. The mass balance closure is used to check the reliability of the adhesion amount M measurement results. In addition, the ratio of the amount trapped by the filter screen to the amount of salt adhering to the pipe wall can also distinguish between two mechanisms of action of the coating: anti-adhesion coatings exhibit low adhesion and high trapping, meaning that crystals do not easily remain on the coating surface after formation; nucleation-inhibiting coatings exhibit both low adhesion and trapping. The results of this mechanism distinction can provide a directional basis for coating formulation improvement.

[0059] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Any equivalent substitutions or modifications made to the device structure, sensor arrangement, brine composition, temperature program, or evaluation indicators within the spirit and principles of the present invention shall fall within the protection scope of the present invention.

Claims

1. A method for testing the salt crystallization resistance of pipes, characterized in that, Includes the following steps: S1. The uncoated base tube and the coated tube to be evaluated are shorted together and clamped side by side to form two test tube sections. Liquid enters at one end and exits at the other end of both test tube sections. The outer wall of each test tube section is covered with a wall temperature regulating sleeve. The wall temperature regulating sleeves of the two test tube sections adopt the same structure and are supplied in parallel by the same heat exchange circuit. A wall temperature sensor is also attached to the outer wall of each test tube section. S2. Ensure that the same batch of salt-containing test media is in any one of the following states: saturated, near-saturated, or supersaturated at a preset initial temperature. S3. The salt-containing test medium is circulated through the two test pipe sections in two branches, and the initial flow difference between the two branches is adjusted to a preset equilibrium range. S4. Under circulating flow, the temperature is reduced to the target temperature according to a preset cooling program. The temperature, flow rate, pressure difference, and conductivity of each test tube section are collected online. During the cooling process, the heat exchange capacity of the heat exchange circuit is adjusted according to the difference between the temperature of the salt-containing test medium and the value detected by the wall temperature sensor, so that the wall subcooling of each test tube section is maintained within the preset subcooling range. During the cooling process, the rate of decrease of the collected conductivity is calculated in real time. When the rate of decrease exceeds the preset upper threshold, the cooling is paused or the cooling rate is switched to a preset low speed. When the rate of decrease falls below the preset lower threshold, the preset cooling program is resumed until the temperature reaches the target temperature. During the cooling process, at least one switching operation is also performed to interchange the flow paths of the two branches so that the cumulative flow time of each test tube section on the two branches is the same. The switching time is recorded. S5. Use at least two of the following as endpoint values: test duration, flow rate attenuation rate, pressure difference rise rate, and conductivity change rate. Stop the circulation flow once the endpoint value is reached. S6. Determine the amount of salt crystallization adhering per unit internal surface area of ​​each of the two test pipe sections under the same post-treatment conditions. S7. After pairing and calculating the segmented data before and after the transposition, compare and evaluate the salt crystallization resistance of the two test pipe sections.

2. The method according to claim 1, characterized in that, The uncoated base pipe short and the coated pipe short to be evaluated have the same nominal length and nominal inner diameter, and both were cleaned, dried and weighed before the test.

3. The method according to claim 1, characterized in that, In step S3, the initial flow difference between the two branches is controlled within 10% of the initial flow of the larger branch, and the initial flow rates Qb0 and Qt0, as well as the initial pressure differences ΔPb0 and ΔPt0, are recorded for the branches corresponding to the uncoated base pipe short circuit and the coated pipe to be evaluated short circuit.

4. The method according to claim 1, characterized in that, In step S4, the preset initial temperature is 60℃ to 90℃, and after reaching the preset initial temperature, it is kept at the temperature for 5 min to 60 min before cooling begins; the target temperature is 15℃ to 30℃, and the preset cooling program is linear cooling at a cooling rate of 0.5℃ / h to 10℃ / h, or cooling according to a preset segmented cooling curve.

5. The method according to claim 1, characterized in that, In step S2, the ionic composition, pH, and conductivity of the saline test medium are recorded or adjusted; the saline test medium is oil well produced fluid that has undergone deoiling and degassing treatment, or an artificially prepared salt solution containing one or more of NaCl, CaCl2, MgCl2, Na2SO4, and NaHCO3.

6. The method according to claim 3, characterized in that, In step S5, the flow rate attenuation rate includes the flow rate attenuation rate of the uncoated base pipe short circuit Fb=(Qb0-Qbe) / Qb0 and the flow rate attenuation rate of the coated pipe to be evaluated short circuit Ft=(Qt0-Qte) / Qt0, and the differential pressure rise rate includes the differential pressure rise rate of the uncoated base pipe short circuit Pb=(ΔPbe-ΔPb0) / ΔPb0 and the differential pressure rise rate of the coated pipe to be evaluated short circuit Pt=(ΔPte-ΔPt0) / ΔPt0, where Qbe and Qte are the flow rates of the corresponding branches of the uncoated base pipe short circuit and the coated pipe to be evaluated short circuit at the end of the test, respectively, and ΔPbe and ΔPte are the differential pressures of the uncoated base pipe short circuit and the coated pipe to be evaluated short circuit at the end of the test, respectively.

7. The method according to claim 2, characterized in that, In step S6, the amount of salt crystals adhering per unit internal surface area is calculated as M=(m1-m0) / S, where m0 is the dry mass of the test tube section before the test, m1 is the mass of the test tube section after the test under the same cleaning and drying conditions, and S is the internal surface area of ​​the test tube section. In step S6, each test pipe section is subjected to standardized detachment treatment under the same detachment treatment conditions, and the crystallization adhesion coefficient is calculated according to K=(m2-m0) / (m1-m0), where m2 is the mass of the test pipe section after standardized detachment treatment and drying. In step S7, the salt crystallization resistance rate of the short-circuited coated pipe to be evaluated relative to the short-circuited uncoated base pipe is calculated as η=(Mb-Mt) / Mb×100%, where Mb and Mt are the amount of salt crystallization adhesion per unit internal surface area of ​​the short-circuited uncoated base pipe and the short-circuited coated pipe to be evaluated, respectively.

8. A dynamic experimental apparatus for implementing the method according to any one of claims 1 to 7, characterized in that, It includes a solution tank, a programmable temperature control unit, a circulating pump, a main pipeline, a flow divider assembly, a first vertical test pipe section support assembly, a second vertical test pipe section support assembly, a return pipeline, a sensor assembly, and a data acquisition and control module; The solution tank is used to contain the same batch of saline test medium; the programmable temperature control unit is used to raise the saline test medium to a preset initial temperature, maintain its temperature, and lower it to the target temperature according to a preset cooling program; the inlet of the circulating pump is connected to the solution tank, and the outlet is connected to the diversion assembly via a main pipeline; the diversion assembly is connected to the lower inlet of the first vertical test tube support assembly and the second vertical test tube support assembly respectively; the upper outlet of the first vertical test tube support assembly and the second vertical test tube support assembly is connected to the solution tank via a return pipeline; the sensor assembly is used to collect the temperature, flow rate, and pressure difference corresponding to each test tube section, as well as the conductivity of the saline test medium. The outer wall of each test tube section is covered with a wall temperature regulating sleeve. The two wall temperature regulating sleeves adopt the same structure and are supplied in parallel by the same heat exchange circuit. A wall temperature sensor is also attached to the outer wall of each test tube section. The acquisition and control module is configured to perform branch flow balancing, controlled cooling, online data acquisition, and test endpoint determination. During controlled cooling, the acquisition and control module calculates the rate of decrease of the acquired conductivity in real time. When the rate of decrease exceeds the preset upper threshold, the cooling is paused or the cooling rate is switched to a preset low speed. When the rate of decrease falls back to below the preset lower threshold, the preset cooling program is resumed until the salt-containing test medium drops to the target temperature. The acquisition and control module is also configured to adjust the heat exchange capacity of the heat exchange circuit according to the difference between the temperature of the salt-containing test medium and the detected value of the wall temperature sensor during the controlled cooling process, so that the wall subcooling of each test tube segment is maintained within a preset subcooling range; a reversing valve group is also provided between the flow splitting component and the first vertical test tube segment support component and the second vertical test tube segment support component. The reversing valve group has a straight-through state and a cross state: in the straight-through state, the first branch connects to the first vertical test tube segment support component and the second branch connects to the second vertical test tube segment support component; in the cross state, the flow paths of the two branches are interchanged; the acquisition and control module is also configured to perform at least one reversal operation through the reversing valve group and record the reversal time, and to pair and calculate the segment data before and after the reversal.

9. The dynamic experimental apparatus according to claim 8, characterized in that, The first and second vertical test pipe section support assemblies each include a support frame, an upper sealing joint, a lower sealing joint, and a clamping component. The upper and lower sealing joints are respectively sealed to the threaded or end connection structures at both ends of the test pipe section to form a vertical flow channel with liquid inlet at the bottom and liquid outlet at the top. The flow splitting assembly includes a flow splitter, a first branch flow regulating valve, a second branch flow regulating valve, a first branch flow sensor, and a second branch flow sensor. The acquisition and control module adjusts the first and second branch flow regulating valves according to the detection values ​​of the first and second branch flow sensors to ensure that the initial flow difference between the two branches is within a preset balance range.

10. The dynamic experimental apparatus according to claim 8, characterized in that, The sensor assembly includes a temperature sensor and a flow sensor disposed on the inlet side and / or outlet side of each test tube section, a differential pressure sensor bridging the inlet and outlet of each test tube section, and a conductivity sensor disposed on the solution tank or main pipeline.

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