Method for repairing cracks on inner surface of circumferential weld of pipeline

Abstract

The invention discloses a method for repairing cracks on the inner surface of a circumferential weld of a pipeline, and belongs to the technical field of repairing of cracks on the inner surface of an oil-gas long-distance pipeline. The pipeline circumferential weld inner surface crack repairing method comprises the following steps that machining treatment is conducted on the outer surface, corresponding to the circumferential weld inner surface crack, of a to-be-repaired pipeline; after machining treatment is completed, a reinforcing structure is arranged on the surface of the to-be-repaired pipeline at the circumferential weld in the circumferential direction; the thickness of the reinforcing structure is not smaller than the pipe wall thickness of the to-be-repaired pipeline, and the axial length of the reinforcing structure is not smaller than two times of the sum of the length of the crack ligament of the to-be-repaired pipeline and the thickness of the reinforcing structure. By adding the pipeline reinforcing structure at the external circumferential weld of the to-be-repaired pipeline, the load or deformation of the circumferential weld and the circumferential weld crack is effectively shielded, so that the fracture driving force is reduced to a safe range, and the defect that an existing repairing mode cannot cope with the crack type defect of the inner surface of the circumferential weld of the pipeline is overcome; and the structure cannot effectively cope with geological disasters after the pipeline is repaired.

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 at present are A-type sleeve repair, B-type sleeve repair, epoxy steel sleeve repair, and repair by welding (surfacing). 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 B-type sleeve is also composed of two arc plates with appropriate curvature, but the end part is connected to the pipe by fillet welding. The epoxy steel sleeve is formed by two steel sleeves covering the defect part of the pipe, and the end part of the steel sleeve is sealed by a sealant, and then epoxy resin is injected into the annular gap between the sleeve and the pipe wall. Repair by welding is a process for repairing defects by welding technology, mainly used for repairing defects such as pores, cracks, and slag inclusions. The above four repair technologies cannot resist axial deformation and load because the A-type sleeve and the epoxy steel sleeve only have circumferential bonding force. The B-type sleeve can help the pipe resist part of the axial load due to the fillet weld at the end, but the area of the fillet weld connected to 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 by welding 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 internal surface crack defects.

[0005] Patent No. 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 method for repairing internal surface cracks of pipe girth weld, which fills the gap in the prior art that cannot repair internal surface crack defects of pipe girth weld.

[0008] To achieve the above purpose, one embodiment of the present application provides a method for repairing internal surface cracks of pipe girth weld, comprising the following steps: Mechanically processing the outer surface corresponding to the internal surface crack of the girth weld of the pipe to be repaired; 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; The thickness of the reinforcing structure is not less than the pipe wall thickness of the to-be-repaired pipeline, and the axial length of the reinforcing structure is not less than twice the sum of the crack ligament length of the to-be-repaired pipeline and the thickness of the reinforcing structure; wherein the crack ligament length is the sum of the pipe wall thickness of the to-be-repaired pipeline and the thickness of the reinforcing structure minus the inner surface crack depth. The yield strength of the repaired pipeline is not less than 105% of the yield strength of the base material of the to-be-repaired pipeline, and the impact toughness of the repaired pipeline satisfies that the impact absorbed energy at-20 DEG C is not less than 30J of a single sample and / or 40J of an average of three samples.

[0009] In one of the preferred schemes of the present application, before the outer surface corresponding to the inner surface crack of the girth weld of the to-be-repaired pipeline is subjected to mechanical processing, the position and specification information of the inner surface crack of the to-be-repaired pipeline are determined.

[0010] In one of the preferred schemes of the present application, the mechanical processing of the outer surface corresponding to the inner surface crack of the girth weld of the to-be-repaired pipeline comprises exposing the metal body of the outer surface corresponding to the inner surface crack of the girth weld of the to-be-repaired pipeline.

[0011] In one of the preferred schemes of the present application, the mechanical processing comprises turning and / or milling and / or polishing.

[0012] In one of the preferred schemes of the present application, the mechanical processing of the outer surface corresponding to the inner surface crack of the girth weld of the to-be-repaired pipeline comprises exposing the metal body of the outer surface corresponding to the inner surface crack of the girth weld of the to-be-repaired pipeline.

[0013] In one of the preferred schemes of the present application, after the mechanical processing is completed, the reinforcing structure is arranged circumferentially on the surface of the to-be-repaired pipeline at the girth weld, comprising: circumferentially depositing the welding wire on the surface of the to-be-repaired pipeline at the girth weld to form the reinforcing structure of the pipeline at the girth weld.

[0014] In one of the preferred schemes of the present application, the welding wire comprises the following chemical components 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%, and the balance is Fe and impurities.

[0015] In one preferred scheme of the present application, during the welding, the fusion welding and / or laser-fusion welding and / or cold metal transfer welding is used as the heat source, the welding heat input is 0.5-1.2 kJ / mm, the preheating temperature and the interpass temperature are both 80-150 DEG C, the single-layer thickness of the deposited layer is 2.0-3.5 mm, and the number of deposited layers is greater than or equal to 3.

[0016] In one preferred scheme of the present application, after the welding is completed, the post-weld heat treatment is performed on the reinforcing structure; the heat treatment temperature is 530-570 DEG C, the holding time is greater than or equal to 30 min, and the heating width on each side is greater than or equal to 2t. In the formula, D is the outer diameter of the pipeline to be repaired, and t is the thickness of the reinforcing structure.

[0017] In one preferred scheme of the present application, the reinforcing structure comprises a transition section which is gradually formed by the outer walls at the two axial ends of the reinforcing structure towards the outer wall of the pipeline to be repaired.

[0018] In one preferred scheme of the present application, the length of the transition section is not less than the thickness of the reinforcing structure.

[0019] In summary, the present application has the following advantages: By using the additive manufacturing technology to repair the girth weld, the present application adds a pipeline reinforcing structure similar to a partial sleeve to the outside of the pipeline to be repaired, and the inner surface of the reinforcing pipeline is completely combined with the outer surface of the pipeline to be repaired, thereby increasing the bonding area between the repaired part and the pipeline to be repaired, and improving the structural strength near the girth weld. Therefore, when the pipeline to be repaired is axially deformed, the deformation is not concentrated in the area near the girth weld, and the crack driving force of the circumferential defect of the inner surface is effectively reduced, so that the defect will not crack under the condition of plastic deformation. The repaired pipeline has an axial connection strength and deformation capacity far exceeding the existing pipeline repair technology, and the concentrated deformation of the girth weld can be avoided, thereby preventing crack growth.

[0020] Other features and advantages of the present application will be set forth in the following description, and in part will become apparent to those skilled in the art from the description, or can be learned by practice of the present application. The objects and other advantages of the present application can be realized and attained by the methods and combinations particularly pointed out in the written description and claims hereof. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 FIG. 1 is a schematic view of the pipeline girth weld repair method according to an embodiment of the present application; Figure 2 FIG. 2 is a sectional view of the reinforcing structure according to an embodiment of the present application; Figure 3 FIG. 3 is a flowchart of the pipeline girth weld inner surface crack repair method according to an embodiment of the present application; Figure 4Figure of wide plate tensile test sample containing inner surface crack of girth weld of pipe in blank example of the present application; Figure 5 Schematic diagram of inner surface crack type defect of wide plate tensile test sample in blank example of the present application; Figure 6 Figure of sample morphology after tensile test in blank example of the present application, wherein (a) is the outer surface morphology of sample after tensile test, and (b) is the inner surface morphology of sample after tensile test; Figure 7 Figure of wide plate tensile test sample after inner surface crack repair in example 1 of the present application; Figure 8 Schematic diagram of repaired inner surface crack type defect in example 1 of the present application; Figure 9 Figure of sample morphology after wide plate tensile test in example 1 of the present application; Figure 10 Comparison figure of wide plate tensile test results before and after repair of crack type defect in example 1 of the present application; Figure 11 Comparison figure of wide plate tensile test results before and after repair of crack type defect in comparative example 1 of the present application; Figure 12 Comparison figure of wide plate tensile test results before and after repair of crack type defect in comparative example 2 of the present application; Figure 13 Comparison figure of wide plate tensile test results before and after repair of crack type defect in comparative example 3 of the present application.

[0022] Wherein, 1-pipe, 2-reinforcing structure, 3-girth weld, 4-inner surface crack. DETAILED DESCRIPTION

[0023] In order to make the purpose, technical scheme and advantages of the embodiments of the present application more clear, the technical scheme in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are some embodiments of the present application, but not all the embodiments of the present application. Based on the embodiments in the present application, all the other embodiments obtained by those skilled in the art without creative labor shall fall within the scope of protection of the present application.

[0024] The endpoints of the ranges and any values disclosed in the present application are not limited to the precise values stated. The ranges or values should be interpreted as being approximate. The endpoints of the ranges of values stated are not to be understood as being limited to the exact values recited. The exact values are also specifically disclosed. Any numerical value, however, can only be approximate. Accordingly, the numerical values given are approximate and thus can vary depending upon the desired properties sought to be obtained by the present application. At the very least, each numerical value should be construed in light of the stated preference and scope of equivalents admitted throughout the present specification.

[0025] The application provides a pipeline girth weld inner surface crack repairing method, as shown in the accompanying drawings, comprising the following steps: Figure 1 Step (1): mechanical processing is performed on the outer surface corresponding to the girth weld 3 inner surface crack 4 of the pipeline to be repaired 1; specifically, the mechanical processing comprises the following steps: Step (101): determine the girth weld 3 to be repaired of the pipeline to be repaired 1, and perform excavation operation on the buried pipeline to be repaired 1 to expose the pipeline to be repaired 1 and ensure sufficient operation space; Step (102): determine the position and specification information of the inner surface crack 4 of the pipeline to be repaired 1; Step (103): remove the coating of the girth weld 3 and the adjacent pipeline body of the pipeline to be repaired 1 by mechanical processing means including turning, milling and polishing to expose the metal surface; further, the two adjacent pipelines 1 on both sides of the girth weld 3 are used as a repair section, the metal body of the repair section is exposed by mechanical processing, the length of the repair section is equal to the length of the reinforcing structure 2, and the axial length of the repair section is not less than twice the sum of the crack ligament length and the thickness of the reinforcing structure, wherein the crack ligament length is the sum of the thickness of the pipeline to be repaired 1 and the thickness of the reinforcing structure 2 minus the depth of the inner surface crack 4, that is, the axial length of the repair section is ≥2(T+t-a)+t, wherein T is the wall thickness of the pipeline to be repaired 1, t is the wall thickness of the reinforcing structure 2, and a is the depth of the inner surface crack 4; When turning is used, a circular track is nested on the pipeline to be repaired 1, a turning tool is arranged on the track, the turning tool can move on the track, and the turning tool turns around the peripheral surface of the pipeline to be repaired 1 to turn the pipeline to be repaired 1; Step (2): after the mechanical processing is completed, the reinforcing structure 2 is arranged on the surface of the pipeline to be repaired 1 at the girth weld 3; Preferably, step (2) comprises: welding a welding wire to the surface of the pipeline to be repaired at the girth weld to form a reinforcing structure of the pipeline at the girth weld; wherein the welding wire is a low-alloy high-strength steel gas shielded welding wire, which comprises the following chemical components in percentage by mass: 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%, and the balance is Fe and impurities; Further, a double-layer symmetrical deposition strategy is adopted during welding, UT (ultrasonic testing) or TOFD (time of flight diffraction) is used for interlayer defect screening after each layer of deposition, if defects such as incomplete fusion, pores or slag inclusion are found, polishing and cleaning are required before repair welding, and finally the surface needs to be confirmed to be free of cracks by PT (penetrant testing); ​Further, after the completion of the welding, the reinforcing structure is subjected to local post-weld heat treatment (PWHT), the heat treatment temperature is 530-570℃, the holding time is ≥30min, and the heating width on each side is ≥ wherein D is the outer diameter of the pipeline to be repaired, and t is the thickness of the reinforcing structure, in mm; specifically, the holding time is calculated according to 1.5t min, and when the value of 1.5t is less than 30, the value of the holding time is taken as 30min; wherein the purpose of controlling the heat treatment temperature range is to eliminate the welding residual stress. When the heat treatment temperature is too low, the time for eliminating the residual stress becomes very long, or the purpose of eliminating the welding residual stress cannot be achieved; when the heat treatment temperature is too high, the microstructure of the reinforcing structure will be changed, thereby affecting the performance of the pipeline.

[0026] Step (2) specifically comprises: taking the ground girth weld 3 and the repair section as the matrix, using GMAW (Gas Metal Arc Welding), laser-GMAW composite heat source or CMT (Cold Metal Transfer) power source, controlling the welding heat input at 0.5-1.2kJ / mm, the preheating temperature and the interpass temperature are both 80-150℃, the welding passes need to be polished and cleaned to a metallic luster, the single-pass thickness of the deposited layer is controlled at 2.0-3.5mm, the total number of deposited layers is ≥3, from the top to the bottom of the pipeline to be repaired 1, i.e. 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 matrix, covering the inner surface crack 4 defect in the girth weld 3, and forming the reinforcing structure 2; wherein the thickness of the reinforcing structure 2 is not less than the pipe wall thickness of the pipeline to be repaired 1, i.e. the thickness t of the reinforcing structure 2 ≥T (the pipe wall thickness of the pipeline to be repaired 1); the axial length of the reinforcing structure 2 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 2; wherein the crack ligament length is the sum of the pipe wall thickness of the pipeline to be repaired 1 and the thickness of the reinforcing structure 2 minus the depth of the inner surface crack 4, i.e. L≥2(T+t-a)+t, wherein T is the pipe wall thickness of the pipeline to be repaired 1, t is the thickness of the reinforcing structure 2, a is the depth of the inner surface crack 4, and L is the axial length of the reinforcing structure 2; wherein the total wall thickness after repair minus the maximum depth of the crack is T+t-a, and the total ligament length is 2(T+t-a), the 45° plastic shear band from the crack tip source also has a length of T+t-a on the surface on one side, and the total length on both sides is 2(T+t-a), the thickness t of the reinforcing structure 2 is used to ensure that each side has a length of t / 2 in the single-axial tensile state, and the total length is t; Preferably, the reinforcing structure 2 comprises a transition section, which is formed by gradually approaching the outer wall of the reinforcing structure 2 to the outer wall of the pipeline to be repaired 1 at both axial ends of the reinforcing structure 2, and the transition section comprises two sections, such as Figure 3As shown in the figure, the reinforcing structure 2 is located at one side of the pipeline 1 to be repaired in the shape of an isosceles trapezoid, and the inclined part of the isosceles trapezoid is the transition section, and the length of the transition section is not less than the thickness of the reinforcing structure 2, that is, S >= t, wherein S is the length of the transition section, and t is the wall thickness of the reinforcing structure 2; Preferably, the yield strength of the repaired pipeline 1 is not less than 105% of the yield strength of the base material of the pipeline 1 to be repaired, and the impact toughness of the repaired pipeline 1 satisfies that the impact absorbed energy (KV2) at-20 DEG C is not less than 30J of a single sample and 40J of an average of three samples, so that the reinforcing structure 2 will not be subjected to low-stress brittle fracture.

[0027] The present application effectively solves the problems of insufficient connection area of the bearing part and limited axial deformation capacity of the existing repair technology, thereby obtaining a strongly matched reinforcing structure 2 of the pipeline 1 on the girth weld 3, effectively shielding the load of the girth weld 3 and the crack of the girth weld 3, and enabling the girth weld 3 with a certain size crack to obtain a structure capable of bearing higher axial plastic deformation, thereby avoiding the failure of the girth weld 3 of the pipeline 1 under geological disasters.

[0028] According to the mechanical test and performance prediction results of additive manufacturing, the welding process parameters can be further optimized, the strength and impact toughness of the reinforcing structure are improved, the repair efficiency is further improved, the repair cost is reduced, and the reliability of the welded structure is ensured.

[0029] Blank example For the case of the inner surface crack type defect of the pipeline girth weld, a wide plate tensile test is performed on the pipeline girth weld with an outer diameter of 1219mm and a wall thickness of 22mm to test the tensile strain capacity. The wide plate tensile test sample has a length of 1500mm, a width of 300mm in the gauge section, and the girth weld is located at the middle position. At the same time, the inner surface crack type defect of the girth weld is processed, and the defect depth (a) is 11mm and the length (2c) is 100mm. The appearance of the wide plate tensile test sample containing the inner surface crack of the girth weld of the pipeline before the test is as shown in Figure 4 The inner surface crack type defect of the wide plate tensile test sample is as shown in Figure 5 ; The wide plate tensile test sample containing the inner surface crack of the girth weld of the pipeline is subjected to a tensile test, and the results are as follows: during the wide plate tensile test, the crack expands to penetrate along the wall thickness direction, and failure is achieved. The strain at failure is about 0.45%. The sample appearance after the test is as shown in Figure 6 , wherein Figure 6 (a) is the outer surface appearance of the sample after the tensile test, Figure 6 (b) is the inner surface appearance of the sample after the tensile test, and it can be seen from Figure 6 that the crack expands to penetrate Figure 6 to the outer surface in (a), Figure 6 and the inner surface crack opening can be seen in (b). Example 1 For the case of inner surface crack type defect in pipe girth weld, the pipe girth weld with outer diameter of 1219 mm and wall thickness of 22 mm was repaired by using the repair method of the present application, and then the repaired structure of the girth weld was subjected to wide plate tensile test to test its tensile strain capacity. The repair parameters met the aforementioned "detailed description" of the present application. The length of the wide plate tensile test sample was 1500 mm, the width within the gauge length was 300 mm, and the girth weld was located at the middle position. At the same time, the inner surface crack type defect of the girth weld was processed, and the defect depth (a) was 11 mm and the length (2c) was 100 mm. The wide plate tensile test sample after repair of the inner surface crack is shown in Figure 7 , and the repaired inner surface crack type defect diagram is shown in Figure 8 .

[0030] The wide plate tensile test sample after repair of the inner surface crack was subjected to tensile test, and the results were as follows: during the wide plate tensile test, the crack did not crack, and the final sample failed in the form of necking at the base material position and plastic collapse, and the failure strain reached more than 2%. The sample morphology after test is shown in Figure 9 , Figure 9 The necking area is circled in the middle, and the comparison of wide plate tensile test results before and after repair of the crack type defect is shown in Figure 10 .

[0031] Comparative Example 1 For the case of inner surface crack type defect in pipe girth weld, the pipe girth weld with outer diameter of 1219 mm and wall thickness of 22 mm was repaired by using the repair method of the present application, and then the repaired structure of the girth weld was subjected to wide plate tensile test to test its tensile strain capacity. To verify the rationality of the repair parameters, on the basis of the technical solution of the present application, the thickness of the repair reinforcing structure was changed to 1 / 2 of the original wall thickness T of the structure to be repaired, i.e. 11 mm.

[0032] The wide plate tensile test sample after repair of the inner surface crack was subjected to tensile test, and the results were as follows: axial tensile strain was applied to the repaired pipe, and during the application process, the inner surface defect depth of the original pipe girth weld was 11 mm, the ligament length (the thickness of the uncracked part of the original wall) was 11 mm, and the total wall thickness including the repair part was 22 mm. Due to the fluctuation of crack depth and the existence of plastic zone at the crack tip, the net cross-sectional area at the crack was smaller than that without crack, so under the action of displacement-controlled load (forced strain), local strain was concentrated, and then the crack initiated and expanded under the action of large strain. Taking crack initiation as the failure criterion, the far-end strain at failure was not more than 0.5%. The comparison of wide plate tensile test results before and after repair of the crack type defect is shown in Figure 11 .

[0033] Comparative Example 2 For the case of inner surface crack type defect in pipe girth weld, the pipe girth weld with an outer diameter of 1219 mm and a wall thickness of 22 mm is repaired by using the partial repair method of the present application, and then a full-size tensile test is performed on the repaired structure of the girth weld to test the tensile strain capacity thereof. In order to verify the rationality of the repair parameters, on the basis of the foregoing technical solution of the present application, the length of the repair reinforcing structure is changed to be less than twice the crack ligament length 2(2T-a)=66, and the integer typical value is 50 mm.

[0034] The repaired wide plate tensile test sample after the inner surface crack is subjected to a tensile test, and the results are as follows: axial tensile strain is applied to the repaired pipe, the ligament length of the inner surface crack on the original pipe girth weld is 33 mm, and during the deformation application process, a plastic zone of about 45° is generated at the crack tip. Since the length of the repair reinforcing structure is less than twice the crack ligament length, after the plastic zone extends to the surface of the repair reinforcing structure, the structure reaches full cross-section yield, and the sample fails in a plastic collapse mode, with a failure strain of about 1.5%, which is lower than the level of full cross-section uniform tensile strain necking (more than 2%). The comparison of the wide plate tensile test results before and after the crack type defect is repaired is shown in Table 1. Figure 12

[0035] Comparative Example 3 For the case of inner surface crack type defect in pipe girth weld, the pipe girth weld with an outer diameter of 1219 mm and a wall thickness of 22 mm is repaired by using the partial repair method of the present application, and then a full-size tensile test is performed on the repaired structure of the girth weld to test the tensile strain capacity thereof. In order to verify the rationality of the repair parameters, on the basis of the foregoing technical solution of the present application, the length of the repair reinforcing structure is changed to be less than twice the crack ligament length 2(2T-a)=66, and the integer typical value is 50 mm.

[0036] The repaired wide plate tensile test sample after the inner surface crack is subjected to a tensile test, and the results are as follows: axial tensile strain is applied to the repaired pipe, the ligament length of the inner surface crack on the original pipe girth weld is 33 mm, and during the deformation application process, a plastic zone of about 45° is generated at the crack tip. Since the length of the repair reinforcing structure is less than twice the crack ligament length, after the plastic zone extends to the surface of the repair reinforcing structure, the structure reaches full cross-section yield, and the sample fails in a plastic collapse mode, with a failure strain of about 1.5%, which is lower than the level of full cross-section uniform tensile strain necking (more than 2%). The comparison of the wide plate tensile test results before and after the crack type defect is repaired is shown in Table 1. Figure 13

[0037] The effects before and after repair of the blank example, Example 1, and Comparative Examples 1-3 are compared, and the results are shown in Table 1.

[0038] Table 1: Comparison of effects of blank example, Example 1, and Comparative Examples 1-3 ​​

[0039] Notes: A is blank example compared with example 1, that is, the comparison between the defective pipe girth weld and the repaired pipe girth weld after the repair according to the present application; B is the comparison between example 1 and comparative example 1, that is, the comparison between the repaired pipe girth weld according to the present application and the repaired structure with a thickness less than the requirement of the present application; C is the comparison between example 1 and comparative example 2, that is, the comparison between the repaired pipe girth weld according to the present application and the repaired structure with a length less than the requirement of the present application; D is the comparison between example 1 and comparative example 3, that is, the comparison between the repaired pipe girth weld according to the present application and the repaired structure with a strength and toughness less than the requirement of the present application.

[0040] As can be seen from Table 1, the performance of the sample repaired by the repair method according to the present application in example 1 is better than that of the samples repaired by comparative examples 1-3, thereby illustrating that the repair method according to the present application makes the defect not crack under the condition of plastic deformation, and the repaired pipe has an axial connection strength and deformation capacity far exceeding the existing pipe repair technology, but the reinforcing structure needs to meet the repair parameter range defined by the present application.

[0041] In summary, the present application repairs the girth weld by using the additive manufacturing technology, adds a pipe reinforcing structure similar to a partial sleeve to the outside of the pipe to be repaired, combines the inner surface of the reinforcing pipe with the outer surface of the pipe to be repaired into one body, improves the bonding area of the repaired part bearing structure and the surface of the pipe to be repaired, makes the structural strength near the girth weld higher than that of the pipe to be repaired, effectively shields the load and deformation (displacement controlled load) of the girth weld and girth weld crack, thereby reduces the crack driving force to a safe range, and makes the girth weld with a certain size crack have the ability to withstand higher axial plastic deformation.

[0042] The above-described examples only describe the preferred embodiments of the present application, and do not limit the scope of the present application. Without departing from the design spirit of the present application, various modifications and improvements to the technical solutions of the present application made by ordinary engineering technicians in the art shall fall within the protection scope determined by the claims of the present application.

Claims

1. A method of repairing an internal surface crack in a girth weld of a pipe, characterized by, The method comprises the following steps: Mechanical processing is performed on the outer surface corresponding to the inner surface crack of the girth weld of the pipe to be repaired; 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; The thickness of the reinforcing structure is not less than the pipe 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 crack ligament length of the pipe to be repaired and the thickness of the reinforcing structure; wherein the crack ligament length is the sum of the pipe wall thickness of the pipe to be repaired and the thickness of the reinforcing structure minus the depth of the inner surface crack; The yield strength of the repaired pipe is not less than 105% of the yield strength of the base material of the pipe to be repaired, and the impact toughness of the repaired pipe satisfies that the impact absorbed energy at-20 ℃ is not less than 30 J for a single sample and / or 40 J for an average of three samples.

2. A method of repairing an internal surface crack in a girth weld of a pipe as defined in claim 1, characterized by: Before the mechanical processing is performed on the outer surface corresponding to the inner surface crack of the girth weld of the pipe to be repaired, the position and specification information of the inner surface crack of the pipe to be repaired are determined.

3. A method of repairing an internal surface crack in a girth weld of a pipe as defined in claim 1, wherein: The mechanical processing performed on the outer surface corresponding to the inner surface crack of the girth weld of the pipe to be repaired comprises exposing the metal body of the outer surface corresponding to the inner surface crack of the girth weld of the pipe to be repaired.

4. A method of repairing an internal surface crack in a girth weld of a pipe according to claim 1 or 3, characterized in that: The mechanical processing comprises turning and / or milling and / or polishing.

5. A method of repairing an internal surface crack in a girth weld of a pipe as defined in claim 1, wherein: The mechanical processing performed on the outer surface corresponding to the inner surface crack of the girth weld of the pipe to be repaired comprises exposing the metal body of the repair section by mechanical processing, and the axial length of the repair section is not less than twice the sum of the crack ligament length of the pipe to be repaired and the thickness of the reinforcing structure.

6. A method of repairing an internal surface crack in a girth weld of a pipe as defined in claim 1, wherein: 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, which comprises circumferentially depositing welding wires on the surface of the pipe to be repaired at the girth weld to form the reinforcing structure of the pipe at the girth weld.

7. A method of repairing an internal surface crack in a girth weld of a pipe as defined in claim 6, wherein: The welding wires comprise the following chemical components in percentage by mass: 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%, and the balance being Fe and impurities.

8. A method of repairing an internal surface crack in a girth weld of a pipe as defined in claim 6, wherein: During the 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 0.5 kJ / mm-1.2 kJ / mm, the preheating temperature and the interpass temperature are both 80 ℃-150 ℃, the single-pass thickness of the deposited layer is 2.0 mm-3.5 mm, and the number of deposited layers is ≥3.

9. A method of repairing an internal surface crack in a girth weld of a pipe as defined in claim 6, wherein: After the welding is completed, the reinforcing structure is subjected to post-weld heat treatment; the heat treatment temperature is 530-570 ℃, the holding time is ≥30 min, and the heating width on each side is ≥ D is the outer diameter of the pipe to be repaired, and t is the thickness of the reinforcing structure.

10. A method of repairing an internal surface crack in a girth weld of a pipe as defined in claim 1, wherein: The reinforcing structure comprises a transition section which is gradually formed by the outer walls at the two axial ends of the reinforcing structure approaching the outer wall of the pipe to be repaired.

11. A method of repairing an internal surface crack in a girth weld of a pipe as defined in claim 10, wherein: The length of the transition section is not less than the thickness of the reinforcing structure.

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