Pipeline repair welding heat exchange simulation device and simulation method

Abstract

The invention belongs to the technical field of pipeline repair, and provides a pipeline repair welding heat exchange simulation device and method.The device comprises a pipeline, a B-type sleeve, a compressed air bottle and a liquid nitrogen bottle; one end of the pipeline is provided with a thermometer, and the other end of the pipeline is communicated with a compressed air bottle and a liquid nitrogen bottle through air pipes; the B-type sleeve is welded on the surface of the pipeline, and the welding position is an in-service welding seam; the compressed air bottle is used for introducing air into the pipeline; and the liquid nitrogen bottle is used for introducing nitrogen into the pipeline. According to the device, a mixed cooling medium is introduced into the pipeline through the compressed air bottle and the liquid nitrogen bottle, and a temperature difference can be generated between the inner wall and the outer wall of the pipeline, so that the actual working condition of the pipeline can be effectively simulated, and a simulation device is provided for studying the hardening condition of the pipeline; the test conditions reach or even exceed the same construction site conditions, and hardware support is provided for research of the pipeline repair technology.

Description

Technical Field

[0001] The present invention belongs to the technical field of pipeline repair, and particularly relates to a pipeline repair welding heat exchange simulation device and a simulation method. Background Art

[0002] In-service welding repair refers to a welding repair of a pipeline without stopping the transportation, which ensures the continuous operation of the pipeline. It is an environmentally friendly, economical and efficient repair method with broad development prospects. There are mainly two problems in the welding of in-service pipeline systems. One is to avoid "burn-through", that is, the welding arc burns the pipe wall and causes rupture. On the other hand, hydrogen-induced cracks are mainly caused by the acceleration of the heat dissipation of the pipe wall by the flowing medium inside the pipeline, which increases the welding cooling rate. The generation of hydrogen-induced cracks should simultaneously meet three conditions: the oxygen content in the weld, the hardening tendency of the welded joint, and the restraint stress borne by the welded joint. If one of these conditions is not met, the generation of hydrogen-induced cracks can be avoided. When welding an in-service pipeline system, the use of low-hydrogen electrodes or low-hydrogen welding process methods, as well as methods to reduce the formation of hardened structures (when the low-hydrogen level cannot be guaranteed) can effectively avoid hydrogen-induced cracks. At the same time, after experiencing the complex thermal cycle process of rapid non-uniform heating and cooling during welding, the performance of the welding molten pool, especially the heat-affected zone (HAZ) of the weld, often seriously mismatches with the performance of the pipe material itself, leading to service safety and reliability problems. To avoid hydrogen-induced cracking, the most commonly used method is to adopt a sufficient heat input to overcome the influence of the flowing medium.

[0003] At present, the method of adopting the preheating or temper bead deposition sequence can also reduce the generation of hydrogen-induced cracks. However, when welding some in-service pipeline systems, due to the heat dissipation of the conveying medium, it is difficult to preheat. There are various existing methods for predicting the heat input, including computer simulation thermal analysis to predict the heat input required in welding production, but it cannot replace the welding process qualification. Studying the influence laws of different flowing media cooling environments inside the pipeline and different welding processes on the comprehensive performance of in-service welding of pipelines. However, due to the great danger of in-service welding of actual oil and gas pipelines and the high test cost, it is necessary to simulate the in-service welding environment in the laboratory for research and evaluation. Internationally, water is mostly used as the flowing medium for in-service welding research. API 1104 and Appendix of GB / T 31032 stipulate that "when welding a test joint, the test pipe is filled with water, and the thermal conditions when the water flows through the test section are the same as or more severe than those at the construction site". However, there are some problems in the implementation process of this method. For example, the limited volume of the pipe cavity, the untimely control of the water flow velocity at the inlet and outlet of the device, etc. will cause untimely heat dissipation at the test section, and it is difficult to achieve the same construction site conditions in the test. Summary of the Invention

[0004] To solve at least one problem in the background art, the present invention provides a simulation device and a simulation method for heat exchange in pipeline repair welding.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] A simulation device for heat exchange in pipeline repair welding includes a pipeline, a B-shaped sleeve, a compressed air cylinder, and a liquid nitrogen cylinder;

[0007] Both ends of the pipeline are sealed. A thermometer is installed at one end, and the other end is connected to the compressed air cylinder and the liquid nitrogen cylinder through an air pipe;

[0008] The B-shaped sleeve is welded on the surface of the pipeline, and the welding position is the in-service welding seam;

[0009] The compressed air cylinder is used to introduce air into the pipeline;

[0010] The liquid nitrogen cylinder is used to introduce nitrogen into the pipeline.

[0011] Preferably, the compressed air cylinder and the liquid nitrogen cylinder are respectively connected with air pipes. One ends of the two air pipes are connected with a confluence air pipe, and the confluence air pipe is connected to the pipeline.

[0012] Preferably, valves are installed on the air pipes.

[0013] Preferably, a flow meter is installed on the confluence air pipe.

[0014] A simulation method for the above simulation device for heat exchange in pipeline repair welding includes the following steps:

[0015] Control the opening degree of the valve and introduce a cooling medium into the pipeline;

[0016] Weld the pipeline and the B-shaped sleeve;

[0017] Calculate the temperature change of the pipeline with the wall thickness.

[0018] Preferably, controlling the opening degree of the valve and introducing a cooling medium into the pipeline includes the following steps:

[0019] Adjust the input temperature of the cooling medium;

[0020] Adjust the flow rate of the cooling medium.

[0021] Preferably, the cooling medium is air or nitrogen or a mixed gas of air and nitrogen.

[0022] Preferably, the input temperature is:

[0023] T = (v 1 × T 1 + v 2 × T2 ) / (v 1 +v 2 );

[0024] Wherein, T is the input temperature, v 1 is the air flow rate, T 1 is the nitrogen temperature, v 2 is the nitrogen flow rate, T 2 is the nitrogen temperature;

[0025] The flow rate of the cooling medium is the sum of the cooling medium entering the pipeline per unit time, which is equal to the product of the flow velocity of the cooling medium and the unit time.

[0026] Preferably, calculating the temperature change of the pipeline with the wall thickness includes the following steps:

[0027] Obtain the temperature of the inner wall of the pipeline;

[0028] Obtain the temperature of the outer wall of the pipeline;

[0029] Calculate the heat conduction temperature at any wall thickness of the pipeline based on the temperature of the inner wall and the outer wall of the pipeline.

[0030] Preferably, the heat conduction temperature at any wall thickness of the pipeline satisfies:

[0031]

[0032] Wherein, T h is the heat conduction temperature with a wall thickness of h; T 外 is the temperature of the outer wall of the pipeline; T 内 is the temperature of the inner wall of the pipeline, and the inner wall temperature is equal to the temperature of the cooling medium; A 1 and A 2 are conversion coefficients; X is the heat flow direction.

[0033] Advantages of the present invention:

[0034] 1. The device of the present invention uses a compressed air bottle and a liquid nitrogen bottle to introduce a mixed cooling medium into the pipeline, which can generate a temperature difference between the inner wall and the outer wall of the pipeline, thereby effectively simulating the actual working conditions of the pipeline, providing a simulation device for studying the hardening of the pipeline, making the test conditions reach or even exceed the same construction site conditions, and providing hardware support for the research of pipeline repair technology;

[0035] 2. The present invention provides a method for simulating heat exchange in repair welding of in-service pipelines. By adjusting the temperature and flow rate of the cooling medium inside the pipeline, the temperature gradient attenuation in the wall thickness direction of the pipeline at the welding position is controlled, so that the undercooling degree of the welding temperature near the welding pool is close to or more severe than the actual working conditions. This patent overcomes the problem of untimely heat dissipation in the test section of the original method. By regulating the temperature and flow rate of the cooling medium, a large amount of heat can be effectively removed, and the temperature of the test section can be quickly, flexibly and effectively regulated to meet the actual non-stop transportation working conditions.

[0036] Other features and advantages of the present invention will be described in the following specification, and, in part, will be obvious from the specification, or will be understood by implementing the present invention. The objectives and other advantages of the present invention can be achieved and obtained through the structures pointed out in the specification and the drawings. Brief Description of the Drawings

[0037] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following drawings are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0038] Figure 1 Shows a schematic structural diagram of a device for simulating heat exchange in pipeline repair welding of the present invention;

[0039] Figure 2 Shows a schematic diagram of an in-service welding pool of the present invention;

[0040] Figure 3 Shows a schematic diagram of the temperature field distribution in the wall thickness direction of the pipeline at the welding position of the present invention.

[0041] In the figure: 1. Pipeline; 2. B-type sleeve; 3. In-service welding seam; 4. Thermometer; 5. Compressed air bottle; 6. Liquid nitrogen bottle; 7. Valve; 8. Flowmeter; 9. Welding torch tip; 10. Welding pool; 11. Coarse grain zone; 12. Fine grain zone. Detailed Embodiments

[0042] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0043] Embodiment 1

[0044] A simulation device for heat exchange in pipeline repair welding, as Figure 1 shown, includes a pipeline 1, a B-type sleeve 2, a compressed air cylinder 5 and a liquid nitrogen cylinder 6. Both ends of the pipeline 1 are sealed, one end is equipped with a thermometer 4, and the other end is connected to the compressed air cylinder 5 and the liquid nitrogen cylinder 6 through an air pipe. The B-type sleeve 2 is welded on the surface of the pipeline 1, and the welding position is the in-service welding seam 3; the compressed air cylinder 5 is used to introduce air into the pipeline 1, and the liquid nitrogen cylinder 6 is used to introduce nitrogen into the pipeline 1. In addition, the compressed air cylinder 5 and the liquid nitrogen cylinder 6 are respectively connected with air pipes, one ends of the two air pipes are connected with a confluence air pipe, the confluence air pipe is communicated with the pipeline 1, and valves 7 are installed on both air pipes, and the flow rate of the cooling medium can be controlled through the valves 7. A flow meter 8 is also installed on the confluence air pipe, and the flow rate of the cooling medium passing through the confluence pipe per unit time can be calculated through the flow meter 8.

[0045] It should be noted that Figure 1 is the implementation sketch of Example 1. In some specific implementation processes, the valve 7 can adopt an electromagnetic valve to more accurately control the opening degree of the valve 7. In addition, in Figure 1 , the cooling medium is mainly provided by the compressed air cylinder 5 and the liquid nitrogen cylinder 6, and the two can transport compressed low-temperature air and low-temperature nitrogen gas vaporized from liquid nitrogen, so as to ensure that the temperature inside the pipeline 1 is lower than the temperature generated by external welding, and realize heat exchange. Of course, in some specific implementation processes, it is not limited to compressed air and liquid nitrogen as the two cooling media. For example, liquid water, dry ice and other cooling media can also be added, and it should be subject to actual needs.

[0046] It should be further noted that the thermometer 4 is installed at one end of the pipeline 1 in the present invention, and its purpose is to detect the problem of the cooling medium in the pipeline 1, and the temperature of the cooling medium can be considered to be the same as the inner wall temperature of the pipeline 1.

[0047] Furthermore, as shown in the appendix Figure 2 , when repairing and surfacing welding on the outer wall of the pipeline 1, the heat generated by the tip 9 of the welding torch causes a welding molten pool 10 to appear on the outer wall of the pipeline 1, and a coarse grain zone 11 and a fine grain zone 12 caused by welding heat input will be generated around the welding molten pool 10. Generally, the large temperature gradient existing in the outer surface layer area of the welding position will cause a hardened structure to appear near the welding molten pool 10, and then a hydrogen-induced cracking phenomenon will occur, resulting in a problem of delayed cracking at the weld toe position of the weld. In order to effectively simulate the problem of hardening and cracking of the pipeline 1, the device of Example 1 is proposed in the present invention.

[0048] Example 2

[0049] Based on the device of Example 1, a simulation method is proposed, including the following steps:

[0050] S1: Control the opening degree of valve 7 and introduce a cooling medium into pipeline 1, where the cooling medium is air or nitrogen or a mixed gas of air and nitrogen; S2: Weld pipeline 1 and B-type sleeve 2; S3: Calculate the temperature change of pipeline 1 with the wall thickness.

[0051] Further, in S1, it includes the following steps:

[0052] S101: Adjust the input temperature of the cooling medium, where the input temperature is:

[0053] T = (v 1 ×T 1 +v 2 ×T 2 ) / (v 1 +v 2 ); (1)

[0054] In the formula, T is the input temperature, v 1 is the air flow rate, T 1 is the nitrogen temperature, v 2 is the nitrogen flow rate, T 2 is the nitrogen temperature.

[0055] S102: Adjust the flow rate of the cooling medium, where the flow rate of the cooling medium is the total amount of the cooling medium entering pipeline 1 per unit time, which is equal to the product of the flow velocity of the cooling medium and the unit time.

[0056] It should be noted that for pipeline 1 of the present invention, if different materials are used, its thermal conductivity will also cause changes in heat transfer, thus forming different temperature gradients. According to Fourier's law, the definition formula of thermal conductivity is:

[0057] q = -λ(dt / dx); (2)

[0058] Among them, x is the heat flow direction, q is the heat flux density, that is, the heat transferred per unit time in the heat direction; dt / dx is the temperature gradient in the heat flow direction; λ is the thermal conductivity. Different substances have different thermal conductivities, and the thermal conductivity of the same substance will also change due to different state parameters. Generally, the thermal conductivity is regarded as a function of temperature.

[0059] Further, in S3, it includes the following steps:

[0060] S301: Obtain the temperature of the inner wall of pipeline 1; S302: Obtain the temperature of the outer wall of pipeline 1; S303: Calculate the heat conduction temperature at any wall thickness of pipeline 1 based on the temperature of the inner wall and the outer wall of pipeline 1.

[0061] Further, the heat conduction temperature at any wall thickness of pipeline 1 satisfies:

[0062]

[0063] In the formula, T h is the heat conduction temperature with a wall thickness of h; T 外 is the outer wall temperature of pipe 1; T 内 is the inner wall temperature of pipe 1, and the inner wall temperature is equal to the temperature of the cooling medium; A 1 and A 2 are conversion coefficients, where A 1 is taken as 0.055 °C / mm, and A 2 is taken as 0.256 °C / mm 2 ; x is the heat flow direction, that is, the wall thickness direction.

[0064] It should be noted that in the second embodiment, the device of the present invention includes at least the following control modes:

[0065] Mode 1

[0066] Introduce the low-temperature air in the compressed air cylinder 5 into pipe 1, control the opening degree of the valve 7, and at the same time close the valve 7 corresponding to the liquid nitrogen cylinder 6, and then calculate the heat exchange effect of the low-temperature air on pipe 1.

[0067] Mode 2

[0068] Introduce the nitrogen in the liquid nitrogen cylinder 6 into pipe 1, control the opening degree of the valve 7, and at the same time close the valve 7 corresponding to the compressed air cylinder 5, and then calculate the heat exchange effect of the nitrogen on pipe 1.

[0069] Mode 3

[0070] Introduce nitrogen and low-temperature air into pipe 1 at the same time, control the opening degree of the valve 7, and then calculate the heat exchange effect of the mixed gas on pipe 1.

[0071] Mode 4

[0072] Both valves 7 are closed, and then calculate the heat exchange effect of the normal-temperature air on pipe 1.

[0073] Mode 5

[0074] Replace the cooling medium in the compressed air cylinder 5 or the liquid nitrogen cylinder 6 with water, and then separately test the heat exchange effect of water on pipe 1.

[0075] Such as Figure 3As shown, where the straight line A represents the temperature gradient of the empty pipe welding pipe 1 in the wall thickness direction (from the outer wall to the inner wall). During the in-service welding process, due to the continuous welding heat input, the temperature of the outer wall of the pipe 1 remains constant. In the conventional welding evaluation method, there is no medium inside the pipe 1, and the cooling temperature of the inner wall of the pipe 1 is the ambient temperature. Generally, the temperature change in the wall thickness direction of the pipe 1 is approximately linear. The curve B represents the temperature gradient of the in-service welding pipe 1 in the wall thickness direction. Its temperature change is caused by the heat dissipation of the inner wall due to the flow of the conveying medium. Due to the flow of the medium inside the in-service welding pipe 1, the cooling temperature of the inner wall of the pipe 1 is the temperature of the conveying medium. Different medium temperatures and medium flow rates will rapidly carry away a large amount of heat, resulting in a non-linear attenuation of the temperature change of the pipe 1 in the wall thickness direction. The temperature attenuation in the fusion zone of the welding position (the depth range from the outer surface is 0-5 mm) is relatively serious, and it is difficult for the conventional test device method to simulate a similar temperature attenuation method. The curve C represents the welding temperature gradient of the pipe 1 of the device of the present invention in the wall thickness direction. It is mainly caused by the heat dissipation of the inner wall due to the cooling environment. By controlling the flow rate of the mixed gas and continuously inputting a large amount of cooling medium temperature control, the temperature of the inner wall of the pipe 1 is reduced, thereby achieving the subcooling requirement in the fusion zone of the in-service welding position. The heat exchange effect is more obvious than that of the curve B, and it can better simulate the hardening situation of the pipe 1, providing data support for the repair technology of the pipe 1.

[0076] Although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A simulation device for heat exchange in pipeline repair welding, characterized in that, it includes a pipeline (1), a B-type sleeve (2), a compressed air bottle (5) and a liquid nitrogen bottle (6); Both ends of the pipeline (1) are sealed, with a thermometer (4) installed at one end, and the other end is connected to the compressed air bottle (5) and the liquid nitrogen bottle (6) through an air pipe; The B-type sleeve (2) is welded on the surface of the pipeline (1), and the welding place is the in-service welding seam (3); The compressed air bottle (5) is used to introduce air into the pipeline (1); The liquid nitrogen bottle (6) is used to introduce nitrogen into the pipeline (1).

2. The simulation device for heat exchange in pipeline repair welding according to claim 1, characterized in that, The compressed air bottle (5) and the liquid nitrogen bottle (6) are respectively connected with air pipes, one ends of the two air pipes are connected with a confluence air pipe, and the confluence air pipe is communicated with the pipeline (1).

3. The simulation device for heat exchange in pipeline repair welding according to claim 2, characterized in that, A valve (7) is installed on the air pipe.

4. The simulation device for heat exchange in pipeline repair welding according to claim 2, characterized in that, A flowmeter (8) is installed on the confluence air pipe.

5. A simulation method, characterized in that, for the simulation device for heat exchange in pipeline repair welding according to any one of claims 1-4, including the following steps: Control the opening degree of the valve (7) and introduce a cooling medium into the pipeline (1); Weld the pipeline (1) and the B-type sleeve (2); Calculate the temperature change of the pipeline (1) with the wall thickness.

6. The simulation method according to claim 5, characterized in that, Controlling the opening degree of the valve (7) and introducing a cooling medium into the pipeline (1) includes the following steps: Adjust the input temperature of the cooling medium; Adjust the flow rate of the cooling medium.

7. The simulation method according to claim 6, characterized in that, The cooling medium is air or nitrogen or a mixed gas of air and nitrogen.

8. The simulation method according to claim 7, characterized in that, The input temperature is: T = (v 1 × T 1 + v 2 × T 2 ) / (v 1 + v 2 ); Where T is the input temperature, v 1 is the air flow rate, T 1 is the nitrogen temperature, v 2 is the nitrogen flow rate, T 2 is the nitrogen temperature; The flow rate of the cooling medium is the total sum of the cooling medium entering the pipeline (1) per unit time, which is equal to the product of the flow velocity of the cooling medium and the unit time.

9. The simulation method according to claim 5, characterized in that, Calculating the temperature change of the pipeline (1) with the wall thickness includes the following steps: Obtain the temperature of the inner wall of the pipeline (1); Obtain the temperature of the outer wall of the pipeline (1); Calculate the heat conduction temperature at any wall thickness of the pipeline (1) based on the temperature of the inner wall and the outer wall of the pipeline (1).

10. The simulation method according to claim 9, characterized in that, The heat conduction temperature at any wall thickness of the pipeline (1) satisfies: Where, T h is the heat conduction temperature with a wall thickness of h; T 外 is the outer wall temperature of the pipe (1); T 内 is the inner wall temperature of the pipe (1), and the inner wall temperature is equal to the temperature of the cooling medium; A 1 and A 2 are conversion coefficients; X is the heat flow direction.

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