A method for repairing an internal surface crack in a girth weld of a pipe

Abstract

The application discloses a pipeline girth weld inner surface crack repairing method, and belongs to the technical field of repairing the inner surface crack of an oil and gas long-distance pipeline. The pipeline girth weld inner surface crack repairing method comprises the following steps: performing mechanical processing treatment on the outer surface corresponding to the girth weld inner surface crack of a pipeline to be repaired; after the mechanical processing treatment is completed, a reinforcing structure is arranged circumferentially on the surface of the pipeline to be repaired at the girth weld; the thickness of the reinforcing structure is not less than the pipe wall thickness of the pipeline to be repaired, and the axial length of the reinforcing structure is not less than twice the sum of the crack ligament length of the pipeline to be repaired and the thickness of the reinforcing structure. The pipeline reinforcing structure is added at the outer girth weld of the pipeline to be repaired, so that the load or deformation of the girth weld and the girth weld crack is effectively shielded, the fracture driving force is reduced to a safe range, the defects of the girth weld inner surface crack of the pipeline are solved, and the blank that the structure of the repaired pipeline cannot effectively cope with geological disasters is filled.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of repairing cracks on the inner surface of long-distance oil and gas pipelines, and particularly relates to a method for repairing cracks on the inner surface of a girth weld of a pipeline. BACKGROUND

[0002] The tensile strain capacity is often determined by the effect of girth weld procedure qualification and defect tolerance. The role of the welding procedure qualification is to ensure the equivalence of the welding procedure qualification and field welding by controlling the welding parameters, and the detection of defect tolerance is to ensure that the girth weld meets the service performance requirements under certain load (or deformation) conditions.

[0003] In recent years, with the continuous deepening of oil and gas development and the extension of pipeline construction to complex geological conditions, in order to ensure the strain capacity of the pipeline, the strain-based pipeline design method has been widely used. Due to the possible welding defects and the deterioration of microstructure and / or mechanical properties caused by welding thermal cycle, the girth weld is usually the weakest link in performance. Therefore, in the strain-based pipeline design work, the tensile strain behavior of the girth weld with defects determines the tensile strain capacity of the pipeline. The basic logic is that for the girth weld with the largest allowable defect (a typical specification is an inner surface crack of 50mm long and 3mm deep. Among them, 50mm represents the longest defect length allowed by non-destructive testing, and 3mm represents a typical weld depth), the remote strain or overall strain that triggers its failure is taken as the tensile strain capacity of the pipeline, and the influence of factors such as geometric appearance, material performance, defect size and load conditions on the tensile strain capacity is studied. The most critical criterion for fracture failure behavior is that when the crack driving force (Crack Driving Force, CDF) reaches the threshold value (J or CTOD), unstable fracture occurs, and at this time the remote strain of the crack body, i.e. the tensile strain capacity.

[0004] On the other hand, for the repair of pipe girth weld defects, the commonly used methods are A-type sleeve repair, B-type sleeve repair, epoxy steel sleeve repair, and repair welding (surfacing) repair. Among them, the A-type sleeve is formed by two half-circular column plates covering the defect part of the pipe and welded by side seam. The composition of B-type sleeve is the same as A-type sleeve, which is composed of two arc plates with appropriate arc. But the end of B-type sleeve is connected with the pipe by fillet welding. The epoxy steel sleeve is to cover the defect part of the pipe with two steel sleeves, seal the end of the steel sleeve with a sealant, and then inject epoxy resin into the annular gap between the sleeve and the pipe wall. Repair welding is a process method for repairing defects by welding technology, mainly used for repairing defects such as pores, cracks and slag inclusion. The above four repair technologies, A-type sleeve and epoxy steel sleeve, can only resist the axial deformation and load due to the only circumferential bonding force. While B-type sleeve can help the pipe resist part of the axial load due to the end fillet weld, but the area of the fillet weld connected with the pipe is limited, and the strength of the fillet weld itself cannot be higher than the cross section of the pipe, and it cannot guarantee the safe operation of the pipe containing non-excessive defects under plastic deformation. Once the axial deformation caused by geological disasters such as ground movement occurs, it will still face the risk of failure. The repair welding method directly repairs the defects, so it cannot operate on the internal surface cracks and other defects, and the above four pipe repair methods cannot repair the internal surface crack defects.

[0005] The patent with publication number CN112008192A discloses a pipe girth weld repair method based on additive technology, which repairs the girth weld by using additive manufacturing technology, but the patent does not explicitly repair the internal surface cracks of the pipe, and also does not explicitly propose the repair effect of internal surface defects.

[0006] In summary, the present application provides a method for repairing internal surface cracks of pipe girth weld. SUMMARY

[0007] The purpose of the present application is to provide a pipe girth weld internal surface crack repair method to fill the gap in the prior art that cannot repair the internal surface crack defects of the pipe girth weld.

[0008] To achieve the above purpose, one embodiment of the present application provides a pipe girth weld internal surface crack repair method, comprising the following steps:

[0009] Mechanically processing the outer surface corresponding to the internal surface crack of the girth weld of the pipe to be repaired;

[0010] After the mechanical processing is completed, a reinforcing structure is arranged circumferentially on the surface of the pipe to be repaired at the girth weld;

[0011] The thickness of the reinforcement structure shall not be less than the wall thickness of the pipeline to be repaired, and the axial length of the reinforcement structure shall not be less than twice the sum of the length of the crack ligament of the pipeline to be repaired and the thickness of the reinforcement structure; wherein, the length of the crack ligament is the sum of the wall thickness of the pipeline to be repaired and the thickness of the reinforcement structure minus the crack depth on the inner surface.

[0012] The yield strength of the repaired pipeline shall not be less than 105% of the yield strength of the parent material of the pipeline to be repaired, and the impact toughness of the repaired pipeline shall meet the requirement that the impact absorption energy at -20℃ is not less than 30J for a single specimen and / or 40J for the average value of three specimens.

[0013] One preferred embodiment of the present invention is to determine the location and specifications of the crack on the inner surface of the pipe to be repaired before performing mechanical processing on the outer surface corresponding to the crack on the inner surface of the circumferential weld of the pipe to be repaired.

[0014] One preferred embodiment of the present invention involves machining the outer surface corresponding to the crack on the inner surface of the circumferential weld of the pipeline to be repaired, including: machining the outer surface corresponding to the crack on the inner surface of the circumferential weld of the pipeline to be repaired to expose the metal body of the outer surface corresponding to the crack on the inner surface of the circumferential weld of the pipeline to be repaired.

[0015] In one preferred embodiment of the present invention, the machining includes turning and / or milling and / or grinding.

[0016] One preferred embodiment of the present invention involves machining the outer surface corresponding to the crack on the inner surface of the circumferential weld of the pipeline to be repaired. This includes: taking the adjacent pipelines on both sides of the circumferential weld as repair sections, and exposing the metal body of the repair sections by machining. The axial length of the repair sections is not less than twice the sum of the length of the crack ligament of the pipeline to be repaired and the thickness of the reinforcement structure.

[0017] In one preferred embodiment of the present invention, after the machining process is completed, a reinforcing structure is provided circumferentially on the surface of the pipe to be repaired at the circumferential weld, including: circumferentially depositing welding wire onto the surface of the pipe to be repaired at the circumferential weld to form a reinforcing structure for the pipe at the circumferential weld.

[0018] In one preferred embodiment of the present invention, the welding wire comprises the following chemical composition in the following mass percentages: C: 0.03%-0.08%, Mn: 1.20%-1.80%, Si: 0.40%-0.70%, Ni: 0.50%-1.20%, Mo: 0.20%-0.50%, Cr: ≤0.30%, Cu: ≤0.25%, S≤0.010%, P≤0.015%, Ti: 0.02%-0.05%, with the balance being Fe and impurities.

[0019] In one preferred embodiment of the present invention, during the deposition process, gas metal arc welding and / or laser-gas metal arc welding and / or cold metal transfer welding are used as the heat source, the welding heat input is 0.5kJ / mm-1.2kJ / mm, the preheating temperature and interpass temperature are both 80℃-150℃, the single-pass thickness of the deposited layer is 2.0mm-3.5mm, and the number of deposited layers is ≥3.

[0020] In one preferred embodiment of the present invention, after the welding is completed, the reinforcing structure undergoes post-weld heat treatment; the heat treatment temperature is 530℃-570℃, the holding time is ≥30min, and the heating width on each side is ≥ Where D is the outer diameter of the pipe to be repaired, and t is the thickness of the reinforcement structure.

[0021] In one preferred embodiment of the present invention, the reinforcing structure includes a transition section, which is formed by the outer walls of both ends of the reinforcing structure gradually approaching the outer wall of the pipe to be repaired.

[0022] In one preferred embodiment of the present invention, the length of the transition section is not less than the thickness of the reinforcing structure.

[0023] In summary, the beneficial effects of the present invention are as follows:

[0024] This invention utilizes additive manufacturing technology for circumferential weld repair, adding a sleeve-like reinforcement structure to the outside of the pipe to be repaired. The inner surface of the reinforcement pipe is fully integrated with the outer surface of the pipe to be repaired, increasing the bonding area between the load-bearing structure of the repaired portion and the surface of the pipe to be repaired. This results in a higher structural strength near the circumferential weld than the pipe to be repaired. Therefore, when axial deformation occurs in the pipe to be repaired, the deformation does not concentrate in the area near the circumferential weld, and the crack driving force of circumferential defects on the inner surface is effectively reduced, preventing crack initiation under plastic deformation conditions. The repaired pipe exhibits axial connection strength and deformation capacity far exceeding existing pipe repair technologies, avoiding concentrated deformation of the circumferential weld and thus preventing crack growth.

[0025] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention will be apparent from the effects described in the description and the accompanying drawings. Attached Figure Description

[0026] Figure 1 This is an overall cross-sectional view of the pipeline after the circumferential weld seam has been repaired in an embodiment of the present invention;

[0027] Figure 2 This is a cross-sectional view of the reinforcing structure in an embodiment of the present invention;

[0028] Figure 3This is a flowchart of a method for repairing cracks on the inner surface of a pipe circumferential weld, as described in an embodiment of the present invention.

[0029] Figure 4 This is a tensile test sample of a wide plate containing cracks on the inner surface of the circumferential weld of a pipe, as shown in the blank example of this invention.

[0030] Figure 5 This is a schematic diagram of the crack-type defect on the inner surface of a wide plate tensile test sample in the blank example of this invention.

[0031] Figure 6 The images shown are morphological images of the sample after the tensile test in the blank example of the present invention, wherein (a) is the morphological image of the outer surface of the sample after the tensile test, and (b) is the morphological image of the inner surface of the sample after the tensile test.

[0032] Figure 7 This is a tensile test sample of a wide plate after inner surface crack repair in Embodiment 1 of the present invention;

[0033] Figure 8 This is a diagram of the repaired inner surface crack-type defect in Embodiment 1 of the present invention;

[0034] Figure 9 This is a morphological image of the sample after the tensile test of the wide plate in Embodiment 1 of the present invention;

[0035] Figure 10 This is a comparison diagram of the tensile test results of the wide plate before and after the repair of the crack-type defect in Embodiment 1 of the present invention;

[0036] Figure 11 This is a comparison diagram of the tensile test results of the wide plate before and after the repair of the crack-type defect in Comparative Example 1 of the present invention;

[0037] Figure 12 This is a comparison diagram of the tensile test results of the wide plate before and after the repair of the crack-type defect in Comparative Example 2 of the present invention;

[0038] Figure 13 This is a comparison diagram of the tensile test results of the wide plate before and after the repair of the crack-type defect in Comparative Example 3 of the present invention.

[0039] Among them, 1-pipeline, 2-reinforcing structure, 3-circumferential weld, 4-inner surface crack. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments 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.

[0041] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this invention.

[0042] This invention provides a method for repairing cracks on the inner surface of a pipe circumferential weld, such as... Figure 1 As shown, it includes the following steps:

[0043] Step (1): Perform mechanical processing on the outer surface corresponding to the crack 4 on the inner surface of the circumferential weld 3 of the pipe to be repaired; specifically, this includes:

[0044] Step (101): Determine the circumferential weld 3 that needs to be repaired in the pipeline 1 to be repaired, and carry out excavation work on the buried pipeline 1 to be repaired to expose the pipeline 1 to be repaired and ensure sufficient working space.

[0045] Step (102): Determine the location and specifications of the crack 4 on the inner surface of the pipe 1 to be repaired;

[0046] Step (103): Remove the coating of the circumferential weld 3 and the surrounding pipe body of the pipe to be repaired by machining means, including turning, milling and grinding, to expose the metal surface; further, take the adjacent pipes 1 on both sides of the circumferential weld 3 as the repair section, and expose the metal body of the repair section by machining. The length of the repair section is equal to the length of the following reinforcement structure 2. The axial length of the repair section is not less than twice the sum of the length of the crack ligament of the pipe to be repaired and the thickness of the reinforcement structure. The length of the crack ligament is the sum of the wall thickness of the pipe to be repaired and the thickness of the reinforcement structure 2 minus the depth of the inner surface crack 4, that is, the axial length of the repair section is ≥2(T+ta)+t, where T is the wall thickness of the pipe to be repaired, t is the wall thickness of the reinforcement structure 2, and a is the depth of the inner surface crack 4.

[0047] When using turning, a circular track is nested on the pipe 1 to be repaired, the turning tool is set on the track, and the turning tool can move on the track to turn the pipe 1 around the circumference of the pipe 1 to be repaired.

[0048] Step (2): After the machining is completed, a reinforcing structure 2 is set circumferentially on the surface of the pipe 1 to be repaired at the circumferential weld 3;

[0049] Preferably, step (2) includes: circumferentially depositing welding wire onto the surface of the pipe to be repaired at the circumferential weld, forming a reinforcing structure for the pipe at the circumferential weld; wherein the welding wire is a low-alloy high-strength steel gas-shielded welding wire, comprising the following chemical composition in mass percentage: C: 0.03%-0.08%, Mn: 1.20%-1.80%, Si: 0.40%-0.70%, Ni: 0.50%-1.20%, Mo: 0.20%-0.50%, Cr: ≤0.30%, Cu: ≤0.25%, S≤0.010%, P≤0.015%, Ti: 0.02%-0.05%, with the balance being Fe and impurities;

[0050] Furthermore, a double-pass symmetrical deposition strategy is adopted during the welding process. After each deposition, UT (ultrasonic testing) or TOFD (time difference diffraction method) is used to screen for interlayer defects. If defects such as incomplete fusion, porosity or slag inclusion are found, they need to be ground and removed before re-welding. Finally, the surface needs to be confirmed by PT (penetrating penetration test) to be free of cracks.

[0051] Furthermore, after the welding is completed, the reinforcing structure undergoes localized post-weld heat treatment (PWHT) at a temperature of 530℃-570℃, a holding time of ≥30 minutes, and a heating width of ≥ on each side. Where D is the outer diameter of the pipe to be repaired, and t is the thickness of the reinforcement structure in mm; specifically, the insulation time is calculated based on 1.5t min, where t is the thickness of the reinforcement structure. When the value of 1.5t is less than 30, the insulation time is taken as 30 min.

[0052] The purpose of controlling the heat treatment temperature range is to eliminate residual welding stress. When the heat treatment temperature is too low, the time to eliminate residual stress becomes very long, or the purpose of eliminating residual welding stress is not achieved; when the heat treatment temperature is too high, it will change the microstructure of the reinforcing structure, thereby affecting the performance of the pipeline.

[0053] Step (2) specifically includes: using the ground circumferential weld 3 and the repair section as the base, GMAW (gas metal arc welding), laser-GMAW composite heat source or CMT (cold metal transfer welding) power source is used, the welding heat input is controlled at 0.5-1.2kJ / mm, the preheating temperature and interpass temperature are both 80℃-150℃, the welding passes need to be ground and cleaned to the metallic luster, the single pass thickness of the weld layer is controlled at 2.0-3.5mm, the total number of weld layers is ≥3 layers, from the top to the bottom of the pipe to be repaired 1, that is, from the 12 o'clock position to the 6 o'clock position along the circumference, the welding wire is melted into liquid metal and then deposited onto the surface of the base, covering the crack 4 defect on the inner surface of the circumferential weld 3, forming the reinforcement structure 2;

[0054] The thickness of the reinforcing structure 2 is not less than the wall thickness of the pipe 1 to be repaired, i.e., the thickness t of the reinforcing structure 2 is ≥ T (the wall thickness of the pipe 1 to be repaired); the axial length of the reinforcing structure 2 is not less than twice the sum of the length of the crack ligament of the pipe to be repaired and the thickness of the reinforcing structure 2; wherein, the length of the crack ligament is the sum of the wall thickness of the pipe 1 to be repaired and the thickness of the reinforcing structure 2 minus the depth of the inner surface crack 4, i.e.: L≥2(T+ta)+t, where T is the length of the pipe 1 to be repaired. The wall thickness is t, the thickness of the reinforcing structure 2 is a, the depth of the inner surface crack 4 is L, and the axial length of the reinforcing structure 2 is L. The total ligament length is 2(T+ta) after the total wall thickness after repair minus the maximum crack depth. The 45° plastic shear band originating from the crack tip also has a length of T+ta on one side of the surface, and the total length on both sides is 2(T+ta). The thickness t of the reinforcing structure 2 is used to ensure a uniaxial tensile state with a length of t / 2 on each side, for a total length of t.

[0055] Preferably, the reinforcing structure 2 includes a transition section, which is formed by the outer walls of both ends of the reinforcing structure 2 gradually approaching the outer wall of the pipe 1 to be repaired. The transition section includes two segments, such as... Figure 3 As shown, the reinforcement structure 2 is an isosceles trapezoid located on one side of the pipe 1 to be repaired. The inclined part of the isosceles trapezoid is the transition section. The length of the transition section is not less than the thickness of the reinforcement structure 2, i.e., S≥t, where S is the length of the transition section and t is the wall thickness of the reinforcement structure 2.

[0056] Preferably, the yield strength of the repaired pipe 1 is not less than 105% of the yield strength of the parent material of the pipe 1 to be repaired, and the impact toughness of the repaired pipe 1 meets the requirement that the impact absorption energy (KV2) at -20℃ is not less than 30J for a single specimen and 40J for the average value of three specimens, so that the reinforcing structure 2 will not undergo low-stress brittle fracture.

[0057] This invention effectively solves the problems of insufficient connection area and limited axial deformation capacity of the load-bearing parts in existing repair technologies. As a result, a strongly matched reinforcement structure 2 for the pipeline 1 is obtained on the circumferential weld 3, which effectively shields the load of the circumferential weld 3 and the crack in the circumferential weld 3. This enables the circumferential weld 3 with cracks of a certain size to obtain a structure that can withstand high axial plastic deformation, thus avoiding the failure of the circumferential weld 3 of the pipeline 1 that is prone to occur under geological disaster conditions.

[0058] Based on the performance prediction results of mechanical testing and additive manufacturing, welding process parameters can be further optimized to improve the strength and impact toughness of the reinforced structure, further improve repair efficiency, reduce repair costs, and ensure the reliability of the welded structure.

[0059] Blank example

[0060] For cases where internal surface crack-type defects appear in pipe circumferential welds, wide plate tensile tests were conducted on pipe circumferential welds with an outer diameter of 1219 mm and a wall thickness of 22 mm to test their tensile strain capacity. The wide plate tensile test specimens were 1500 mm long, with a gauge width of 300 mm, and the circumferential weld was located in the middle. Simultaneously, internal surface crack-type defects were machined into the circumferential weld, with a defect depth (a) of 11 mm and a length (2c) of 100 mm. The morphology of the wide plate tensile test specimen containing the internal surface crack of the pipe circumferential weld is shown in the image below. Figure 4 As shown, the crack-type defects on the inner surface of the wide plate tensile test specimen are as follows: Figure 5 As shown;

[0061] Tensile tests were conducted on a wide plate specimen containing a crack on the inner surface of a pipe circumferential weld. The results are as follows: During the tensile test, the crack propagated along the wall thickness direction until it penetrated, reaching failure. The strain at failure was approximately 0.45%. The morphology of the specimen after the test is shown below. Figure 6 As shown, where Figure 6 (a) is a topographic image of the outer surface of the sample after the tensile test. Figure 6 (b) is an image of the inner surface morphology of the sample after the tensile test. Figure 6 It can be seen from this that: the crack extends to penetration ( Figure 6 (a) penetrates to the outer surface. Figure 6 (b) shows the crack opening on the inner surface.

[0062] Example 1

[0063] For cases where internal surface crack-type defects appear in pipe circumferential welds, the repair method of this invention is used to repair circumferential welds with an outer diameter of 1219 mm and a wall thickness of 22 mm. A wide-plate tensile test is then performed on the repaired structure to test its tensile strain capacity. The repair parameters conform to the aforementioned "Specific Embodiments" of this invention. The wide-plate tensile test sample is 1500 mm long, with a gauge width of 300 mm, and the circumferential weld is located in the middle. Simultaneously, the internal surface crack-type defect of the circumferential weld is machined, with a defect depth (a) of 11 mm and a length (2c) of 100 mm. The wide-plate tensile test sample after internal surface crack repair is shown below. Figure 7 As shown in the figure, the repaired inner surface crack-type defect diagram is as follows. Figure 8 As shown.

[0064] Tensile tests were conducted on the wide plate specimens after internal surface crack repair. The results are as follows: During the tensile test, the crack did not initiate. The specimens ultimately failed via necking at the base material location, resulting in plastic collapse, with a failure strain exceeding 2%. Figure 9 As shown, Figure 9 The circled area represents the necking region. The comparison of wide plate tensile test results before and after crack-type defect repair is shown below. Figure 10 As shown.

[0065] Comparative Example 1

[0066] For cases where internal surface crack-type defects occur in pipe circumferential welds, the partial repair method of this invention is used to repair circumferential welds with an outer diameter of 1219 mm and a wall thickness of 22 mm. A full-scale tensile test is then performed on the repaired structure to test its tensile strain capacity. To verify the rationality of the repair parameters, based on the aforementioned technical solution of this invention, the thickness of the repair reinforcement structure is changed to half of the original wall thickness T of the structure to be repaired, i.e., 11 mm.

[0067] Tensile tests were conducted on the wide plate samples after the internal surface cracks were repaired. The results are as follows: Axial tensile strain was applied to the repaired pipe. During the application, the defect depth on the inner surface of the original pipe circumferential weld was 11 mm, the ligament length (the original wall thickness of the uncracked portion) was 11 mm, and the total wall thickness including the repaired portion was 22 mm. Due to the fluctuation of crack depth and the existence of the plastic zone at the crack tip, the net cross-sectional area at the crack was smaller than that at the crack-free area. Therefore, under the displacement-controlled load (forced strain), local strain concentration occurred, and concentrated plastic deformation first occurred at the crack. Then, under the action of large strain, the crack initiation and propagation occurred. Crack initiation was used as the failure criterion, and the strain at the distal end at failure did not exceed 0.5%. Comparison of wide plate tensile test results before and after crack-type defect repair is shown below. Figure 11 As shown.

[0068] Comparative Example 2

[0069] For cases where internal surface crack-type defects appear in pipe circumferential welds, the partial repair method of this invention was used to repair a pipe circumferential weld with an outer diameter of 1219 mm and a wall thickness of 22 mm. A full-scale tensile test was then performed on the repaired structure to test its tensile strain capacity. To verify the rationality of the repair parameters, based on the aforementioned technical solution of this invention, the length of the repair and reinforcement structure was changed to be less than twice the crack ligament length 2(2T-a) = 66, with a typical integer value of 50 mm used here.

[0070] Tensile tests were conducted on the wide plate samples after the internal surface crack was repaired. The results are as follows: Axial tensile strain was applied to the repaired pipe. The ligament length of the internal surface crack on the original pipe's circumferential weld was 33 mm. During deformation, a plastic zone of approximately 45° was generated at the crack tip. Because the length of the repaired reinforcement structure was less than twice the crack ligament length, the plastic zone extended to the surface of the repaired reinforcement structure, at which point the structure reached full-section yielding. The sample failed via plastic collapse, with a failure strain of approximately 1.5%, lower than the level of necking under uniform tensile strain across the entire cross-section (above 2%). A comparison of the wide plate tensile test results before and after crack-type defect repair is provided. Figure 12 As shown.

[0071] Comparative Example 3

[0072] For cases where internal surface crack-type defects appear in pipe circumferential welds, the partial repair method of this invention is used to repair circumferential welds with an outer diameter of 1219 mm and a wall thickness of 22 mm. A full-scale tensile test is then performed on the repaired structure to test its tensile strain capacity. To verify the rationality of the repair parameters, the strength and fracture toughness requirements of the repaired and reinforced structure are removed from the aforementioned technical solution of this invention.

[0073] Tensile tests were conducted on the wide plate samples after the internal surface cracks were repaired. The results are as follows: Axial tensile strain was applied to the repaired pipe. During the deformation process, due to the low strength of the repaired material, concentrated plastic deformation first occurred on the original pipe wall ligament (11 mm thick), causing rapid crack initiation and propagation to the repaired reinforcement structure. Because the toughness of the repaired reinforcement structure was insufficient to prevent crack initiation, the reinforcement structure also rapidly initiated cracking after the crack propagated there, continuing to propagate until structural failure, with a failure strain <1.0%. A comparison of the wide plate tensile test results before and after crack-type defect repair is provided. Figure 13 As shown.

[0074] The effects of the blank example, Example 1, and Comparative Examples 1-3 before and after repair were compared, and the results are shown in Table 1.

[0075] Table 1: Comparison of effects between blank example, Example 1, and Comparative Examples 1-3

[0076]

[0077] Note:

[0078] A is a blank example compared with Example 1, that is: a comparison between the defective circumferential weld of the pipeline and the circumferential weld of the pipeline repaired by the present invention;

[0079] B is a comparison between Example 1 and Comparative Example 1, namely: the thickness of the circumferential weld of the pipeline after repair by the present invention is less than the requirement of the present invention.

[0080] C is a comparison between Example 1 and Comparative Example 2, namely: the length of the pipe circumferential weld and the length of the repaired structure after the solution of the present invention are less than the requirements of the solution of the present invention.

[0081] D represents a comparison between Example 1 and Comparative Example 3, specifically a comparison of the strength and toughness of the pipe circumferential weld after repair using the present invention's solution, which are less than the requirements of the present invention's solution.

[0082] As can be seen from Table 1, the performance of the sample repaired by the repair method of the present invention in Example 1 is better than that of the samples repaired in Comparative Examples 1-3. This shows that the repair method of the present invention prevents the defects from cracking under plastic deformation conditions. The repaired pipe has axial connection strength and deformation capacity that far exceed those of existing pipe repair technologies. However, the reinforcement structure needs to meet the repair parameter range defined by the present invention.

[0083] In summary, this invention uses additive manufacturing technology to repair circumferential welds, adding a pipe reinforcement structure similar to a partial sleeve to the outside of the pipe to be repaired. The inner surface of the reinforcement pipe is completely integrated with the outer surface of the pipe to be repaired, increasing the bonding area between the load-bearing structure of the repaired part and the surface of the pipe to be repaired. This makes the structural strength near the circumferential weld higher than that of the pipe to be repaired, effectively shielding the load and deformation (displacement-controlled load) of the circumferential weld and its cracks, thereby reducing the crack driving force to a safe range and enabling circumferential welds with cracks of a certain size to withstand higher axial plastic deformation.

[0084] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made to the technical solutions of the present invention by those skilled in the art without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for repairing cracks on the inner surface of a pipe circumferential weld, characterized in that, Includes the following steps: The outer surface corresponding to the crack on the inner surface of the circumferential weld of the pipeline to be repaired is machined. After machining, a reinforcing structure is installed circumferentially on the surface of the pipe to be repaired at the circumferential weld. The thickness of the reinforcing structure is not less than the wall thickness of the pipe to be repaired, and the axial length of the reinforcing structure is not less than twice the sum of the length of the crack ligament of the pipe to be repaired and the thickness of the reinforcing structure; wherein, the length of the crack ligament is the sum of the wall thickness of the pipe to be repaired and the thickness of the reinforcing structure minus the crack depth on the inner surface. The yield strength of the repaired pipeline shall not be less than 105% of the yield strength of the base material of the pipeline to be repaired, and the impact toughness of the repaired pipeline shall meet the requirement that the impact absorption energy at -20℃ is not less than 30J for a single specimen and / or 40J for the average value of three specimens. After the machining process is completed, a reinforcing structure is circumferentially set on the surface of the pipe to be repaired at the circumferential weld, including: circumferentially depositing welding wire onto the surface of the pipe to be repaired at the circumferential weld to form a reinforcing structure for the pipe at the circumferential weld. The welding wire comprises the following chemical composition in the following mass percentages: C: 0.03%-0.08%, Mn: 1.20%-1.80%, Si: 0.40%-0.70%, Ni: 0.50%-1.20%, Mo: 0.20%-0.50%, Cr: ≤0.30%, Cu: ≤0.25%, S≤0.010%, P≤0.015%, Ti: 0.02%-0.05%, with the balance being Fe and impurities; During deposition, gas metal arc welding and / or laser-gas metal arc welding and / or cold metal transfer welding are used as heat sources. The welding heat input is 0.5kJ / mm-1.2kJ / mm, the preheating temperature and interpass temperature are both 80℃-150℃, the single-pass thickness of the deposited layer is 2.0mm-3.5mm, and the number of deposited layers is ≥3. After the welding is completed, the reinforcing structure undergoes post-weld heat treatment; the heat treatment temperature is 530℃-570℃, the holding time is ≥30min, and the heating width on each side is ≥ Where D is the outer diameter of the pipe to be repaired, and t is the thickness of the reinforcement structure.

2. The method for repairing cracks on the inner surface of a pipe circumferential weld as described in claim 1, characterized in that: Before machining the outer surface corresponding to the crack on the inner surface of the circumferential weld of the pipeline to be repaired, the location and specifications of the crack on the inner surface of the pipeline to be repaired are determined.

3. The method for repairing cracks on the inner surface of a pipe circumferential weld as described in claim 1, characterized in that: The machining process performed on the outer surface corresponding to the crack on the inner surface of the circumferential weld of the pipeline to be repaired includes: machining the outer surface corresponding to the crack on the inner surface of the circumferential weld of the pipeline to be repaired to expose the metal body on the outer surface corresponding to the crack on the inner surface of the circumferential weld of the pipeline to be repaired.

4. A method for repairing cracks on the inner surface of a pipe circumferential weld as described in claim 1 or 3, characterized in that: The machining includes turning and / or milling and / or grinding.

5. The method for repairing cracks on the inner surface of a pipe circumferential weld as described in claim 1, characterized in that: The mechanical processing of the outer surface corresponding to the crack on the inner surface of the circumferential weld of the pipeline to be repaired includes: taking the adjacent pipelines on both sides of the circumferential weld as the repair section, and exposing the metal body of the repair section by mechanical processing. The axial length of the repair section is not less than twice the sum of the length of the crack ligament of the pipeline to be repaired and the thickness of the reinforcement structure.

6. The method for repairing cracks on the inner surface of a pipe circumferential weld as described in claim 1, characterized in that: The reinforcing structure includes a transition section, which is formed by the outer walls of both ends of the reinforcing structure gradually approaching the outer wall of the pipe to be repaired.

7. The method for repairing cracks on the inner surface of a pipe circumferential weld as described in claim 6, characterized in that: The length of the transition section is not less than the thickness of the reinforcing structure.

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