Alkaline low-hydrogen welding rod for repair X80 manual welding and manufacturing method of alkaline low-hydrogen welding rod

Abstract

The invention belongs to the field of material mechanical property testing, particularly relates to an alkaline low-hydrogen welding rod for X80 manual welding for repair and a manufacturing method thereof, and solves the problem that the alkaline low-hydrogen welding rod for repair welding in X80 pipeline engineering meets high toughness of weld fracture toughness CTOD 0.254 mm. The tensile strength of a repair welded junction of a ring welding joint formed by conducting repair welding through the alkaline low-hydrogen welding rod manufactured through the method is not lower than 625 MPa; the fracture toughness test value of the welding seam and the heat affected zone is greater than or equal to 0.254 mm; the hardness value of weld metal and a heat affected zone of the repaired welded junction is not larger than 300 HV10 through root welding, and the hardness of other zones is not larger than 325 HV10; the single value of the Charpy impact toughness of the repaired welded junction at-20 DEG C is not less than 38J, and the average value is not less than 50J.

Description

Technical Field

[0001] The present invention belongs to the field of testing the mechanical properties of materials, and particularly relates to an alkaline low-hydrogen electrode for manual welding of X80 for repair and its manufacturing method. Background Art

[0002] An electrode is a metal bar that melts and fills the joint of a welded workpiece during gas welding or electric welding. The material of the electrode is usually the same as that of the workpiece. The welding construction standards required for pipeline systems at home and abroad mainly include GB / T 31032-2014, API 1104-2013, CSA Z662-2015, GOST 1603 7-80, AS 2885.2-2016, ISO13847-2013. The requirements and acceptance criteria for the tensile, impact, bending, and notched bar impact of the welds in the above standards are not very different. The number of tests for tensile and bending is determined according to different pipe diameters. The tensile acceptance index should be greater than or equal to the nominal minimum tensile strength of the pipe material. When the fracture occurs in the base metal, the strength not less than 95% of the nominal minimum tensile strength of the pipe material is also considered qualified. The acceptance index of impact toughness (taking X80 grade pipeline steel as an example, X80 represents pipeline steel with a minimum yield strength of 80 kpsi) meets the design requirements or the average value is at least 40 J and the single value is at least 30 J. For the acceptance value requirements of the Charpy V-notch impact test (CTOD), relevant requirements are only available in AS2885.2 and DNV F101. The AS2885.2 standard requires that the results of the CTOD test should meet an average value of 0.15 mm and a minimum value of 0.10 mm, and the DNV F101 standard needs to meet the design requirements, generally 0.15 mm.

[0003] In the petroleum field, long-distance oil and gas pipelines use large-wall-thickness and large-diameter steel pipes, and the strength of the steel pipes is ensured through various alloying elements, tissue types, and grain refinement. Shielded metal arc welding with solid wire and flux-cored arc welding with gas shield are the development directions for welding large-diameter and thick-wall oil and gas pipelines. However, for this welding process, there is little research on the welding applicability of newly developed welding materials for thick-wall and high-grade pipeline steel pipes with different chemical compositions, which hinders the large-scale application of welding materials for girth welds of high-grade oil and gas pipelines. Currently, alkaline low-hydrogen electrodes are mainly used in the repair welding process for welding large-diameter thick-wall oil and gas pipelines. At present, the CTOD values of some electrodes for repair welding in the construction of high-grade oil and gas pipelines are basically between 0.10 and 0.213 mm. There are individual weld joint indicators that meet the requirement of 0.254 mm, but they are not stable. The continuous weld joints for welding process qualification cannot meet the standard requirements of the "National Pipeline Network Group Design and Engineering Construction Code" (abbreviated as DEC). Summary of the Invention

[0004] In view of the above problems, on the one hand, the present invention proposes a manufacturing method for an alkaline low-hydrogen electrode for manual welding of X80 for repair welding, and the method includes the following steps:

[0005] Determine the slag system of the coating of the alkaline low-hydrogen electrode according to the index requirements of the deposited metal of the alkaline low-hydrogen electrode and the mechanical property requirements of the girth weld joint using the alkaline low-hydrogen electrode;

[0006] Determine the composition, mechanical property requirements and wire rod specifications of the wire rod required for producing the alkaline low-hydrogen electrode, and remove the oxide scale from the determined wire rod, draw and cut it into the welding core of the alkaline low-hydrogen electrode;

[0007] Determine the process parameters for producing the coating of the alkaline low-hydrogen electrode and manufacture the alkaline low-hydrogen electrode according to the process parameters;

[0008] Weld the test steel pipe using the manufactured alkaline low-hydrogen electrode and adjust the welding process parameters according to the existing on-site repair welding process regulations to determine the final welding process.

[0009] Further, the index requirements of the deposited metal of the alkaline low-hydrogen electrode include the alloy composition and mechanical properties of the deposited metal;

[0010] Among them, the alloy content and mechanical properties of the chemical composition of the deposited metal need to meet the requirements of GBT32533-2016 high-strength steel electrodes;

[0011] The mechanical properties of the girth weld joint of the alkaline low-hydrogen electrode need to meet the technical regulations for on-line welding of oil and gas pipeline projects.

[0012] Further, the slag system of the coating of the alkaline low-hydrogen electrode is calcium oxide - fluoride - silicon dioxide - titanium dioxide;

[0013] The alloy composition of the deposited metal is as follows:

[0014] 0.065wt% - 0.072wt% C, 1.42wt% - 1.50wt% Mn, 0.28wt% - 0.29wt% Si, 0.0028wt% - 0.0031wt% S, 0.0045wt% - 0.0064wt% P, 2.31wt% - 2.40wt% Ni and 0.14wt% - 0.24wt% Mo.

[0015] Further, the composition of the wire rod required for producing the alkaline low-hydrogen electrode includes alloy components and non-metallic inclusions; among them, the alloy components of the wire rod include:

[0016] 0.068 wt% C, 0.24 wt% Si, 1.30 wt% Mn, 0.0053 wt% P, 0.0031 wt% S, 2.50 wt% Ni, 0.28 wt% Mo, 0.0058 wt% V and 0.028 wt% Cu;

[0017] The non-metallic inclusions in the wire rod include:

[0018] For type A inclusions, the fine series is less than or equal to 1.5 and the coarse series is less than or equal to 1; for type B inclusions, the fine series is less than or equal to 1.5 and the coarse series is less than or equal to 1; for type C inclusions, the fine series is less than or equal to 1.0 and the coarse series is less than or equal to 0.5; for type D inclusions, the fine series is less than or equal to 1.5 and the coarse series is less than or equal to 1.0; for type DS inclusions, it is less than or equal to 1.5.

[0019] Further, the steps of removing the oxide scale from the determined wire rod, drawing and cutting it into the welding core of an alkaline low-hydrogen electrode specifically include the following steps:

[0020] Remove the oxide scale on the surface of the wire rod by mechanical means;

[0021] Draw the wire rod with the oxide scale removed to a preliminary wire rod with the diameter required for the welding core;

[0022] Cut the preliminary wire rod into welding cores with standard lengths according to the requirements of GB / T32533.

[0023] Further, determining the preparation process parameters for the coating of the alkaline low-hydrogen electrode and manufacturing the alkaline low-hydrogen electrode according to the preparation process parameters specifically include:

[0024] Mix the powders according to the slag system of the coating of the alkaline low-hydrogen electrode, where the allowable error for both single materials and the total material is between ±0.3%;

[0025] Mix the prepared powders. During the mixing process, the dry mixing time of the powders is greater than or equal to 15 minutes, and the wet mixing time is 15 - 20 minutes;

[0026] After pre-treating the surface of the welding core, apply and press the prepared powders onto the surface of the welding core. When applying and pressing, there is no oil stain on the surface of the welding core and the temperature is lower than 50°C;

[0027] Bake the welding core with the powders applied and pressed at a temperature of 350 - 400°C to obtain the finished alkaline low-hydrogen electrode.

[0028] Further, adjust the welding process parameters according to the existing on-site repair welding process regulations. Determining the final welding process parameters includes the following steps:

[0029] Determine the welding process parameters that need to be adjusted. The welding process parameters include welding current, welding speed, inter-pass temperature, and welding position;

[0030] Examine the welding processability of basic low-hydrogen electrodes. The examination indicators include arc stability, arc appearance, droplet transfer state, molten pool fluidity, wire feeding stability, spatter, and forming appearance.

[0031] In the laboratory, compare the surface forming of flat welding, horizontal welding, vertical welding, and overhead welding under different welding currents and the mechanical properties of the deposited metal after welding.

[0032] Determine the final welding process based on the results of the examination of welding processability and the mechanical properties of the deposited metal at different welding positions under different welding currents.

[0033] Furthermore, the manufacturing method further includes evaluating the final welding process after determining the final welding process.

[0034] Furthermore, the evaluation of the final welding process includes:

[0035] Weld the circumferential weld of the test steel pipe well according to the final welding process using the basic low-hydrogen electrode and perform non-destructive testing.

[0036] If the circumferential weld of the test steel pipe passes the non-destructive testing, then cut and machine the tensile test specimen of the circumferential weld, the hardness test specimen of the circumferential weld along the wall thickness direction, the impact toughness specimens at different positions of the weld and the fusion line, and the CTOD specimens at different positions of the fusion line and the heat-affected zone.

[0037] Test the tensile properties of the processed circumferential weld as a transverse plate specimen and record the fracture position; if the fracture position is on the base metal and the tensile strength is greater than or equal to 95% of the nominal strength of the pipe material, it is judged as qualified; if the fracture position is on the weld and the tensile strength is greater than or equal to the nominal strength of the pipe material, it is judged as qualified.

[0038] On the other hand, this aspect proposes a basic low-hydrogen electrode for X80 manual welding for repair manufactured by the described manufacturing method.

[0039] Furthermore, the circumferential weld joint formed by repair welding using the basic low-hydrogen electrode has the following characteristics:

[0040] The tensile strength of the repaired weld is not less than 625 MPa;

[0041] The fracture toughness test values of the weld and the heat-affected zone are greater than or equal to 0.254 mm;

[0042] The hardness value of the root pass of the weld metal and the heat-affected zone of the repaired weld is less than or equal to 300 HV 10 , and the hardness of the remaining areas is less than or equal to 325 HV 10 ;

[0043] The single value of the -20°C Charpy impact toughness of the repaired weld joint shall not be less than 38 J, and the average value shall not be less than 50 J.

[0044] Advantages of the present invention:

[0045] The basic low-hydrogen electrode proposed by the present invention solves the problem of high toughness of the basic low-hydrogen electrode for repair welding in the X80 pipeline project to meet the weld fracture toughness CTOD of 0.254 mm. The tensile strength of the repaired weld joint formed by repairing welding with the basic low-hydrogen electrode manufactured by the present invention shall not be less than 625 MPa; the fracture toughness test values of the weld and the heat-affected zone shall be greater than or equal to 0.254 mm; the hardness value of the root pass of the weld metal and the heat-affected zone of the repaired weld joint shall not be greater than 300 HV 10 , and the hardness of the remaining areas shall not be greater than 325 HV 10 ; the single value of the -20°C Charpy impact toughness of the repaired weld joint shall not be less than 38 J, and the average value shall not be less than 50.

[0046] Other features and advantages of the present invention will be described in the subsequent specification, and in part, will become apparent 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 by the structures pointed out in the specification, claims, and drawings. Brief Description of the Drawings

[0047] 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 the description of the embodiments or the prior art. Obviously, the drawings in the following description 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.

[0048] Figure 1 Shows a flowchart of a manufacturing method of a basic low-hydrogen electrode for X80 manual welding for repair proposed by the present invention;

[0049] Figure 2 Is the flat position welding appearance diagram of the basic low-hydrogen electrode of the present invention at 150 A current;

[0050] Figure 3 Is the flat position welding appearance diagram of the basic low-hydrogen electrode of the present invention at 170 A current;

[0051] Figure 4 Is the flat position welding appearance diagram of the basic low-hydrogen electrode of the present invention at 190 A current;

[0052] Figure 5 Is the horizontal position welding weld formation diagram of the present invention at 150 A current;

[0053] Figure 6 Is the fillet weld formation diagram of the present invention at 150 A current;

[0054] Figure 7 This is the weld formation diagram of the 150A current vertical fillet weld of the present invention;

[0055] Figure 8 Sampling position diagram of the fracture toughness (SENB) specimen of the heat affected zone of the present invention in the wall thickness direction;

[0056] Figure 9 This is the notch position of the WP specimen for the fracture toughness CTOD test of the present invention;

[0057] Figure 10 Schematic diagram of the specimen sampling position in the embodiment of the present invention;

[0058] Figure 11 Full weld tensile stress-strain curve diagram in the embodiment of the present invention;

[0059] Figure 12 Schematic diagram of the indentation position of the Vickers hardness test in the embodiment of the present invention;

[0060] Figure 13 Macrograph of the weld joint 1#M2 (repaired weld) in the embodiment of the present invention;

[0061] Figure 14 Macrograph of the weld joint 2#M2 (repaired weld) in the embodiment of the present invention;

[0062] Figure 15 Experimental curve and fracture surface morphology diagram of the weld joint 1# weld (D1-WM) in the embodiment of the present invention;

[0063] Figure 16 Experimental curve and fracture surface morphology diagram of the heat affected zone (D1-HAZ) of the weld joint 1# in the embodiment of the present invention;

[0064] Figure 17 Experimental curve and fracture surface morphology diagram of the weld joint 1# weld (D2-WM) in the embodiment of the present invention;

[0065] Figure 18 Experimental curve and fracture surface morphology diagram of the heat affected zone (D2-HAZ) of the weld joint 1# in the embodiment of the present invention;

[0066] Figure 19 Experimental curve and fracture surface morphology diagram of the weld joint 1# weld (D3-WM) in the embodiment of the present invention;

[0067] Figure 20 Experimental curve and fracture surface morphology diagram of the heat affected zone (D3-HAZ) of the weld joint 1# in the embodiment of the present invention;

[0068] Figure 21For the experimental curve and fracture morphology diagram of the weld seam (D1-WM) of the 2# weld in the embodiments of the present invention;

[0069] Figure 22 For the experimental curve and fracture morphology diagram of the heat affected zone (D1-HAZ) of the 2# weld in the embodiments of the present invention;

[0070] Figure 23 For the experimental curve and fracture morphology diagram of the weld seam (D2-WM) of the 2# weld in the embodiments of the present invention;

[0071] Figure 24 For the experimental curve and fracture morphology diagram of the heat affected zone (D2-HAZ) of the 2# weld in the embodiments of the present invention;

[0072] Figure 25 For the experimental curve and fracture morphology diagram of the weld seam (D3-WM) of the 2# weld in the embodiments of the present invention;

[0073] Figure 26 For the experimental curve and fracture morphology diagram of the heat affected zone (D3-HAZ) of the 2# weld in the embodiments of the present invention. Detailed implementation manners

[0074] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some but not all of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0075] X80 is a high-strength pipeline steel, indicating a pipeline steel with a minimum yield strength of 80 kpsi, that is, the minimum yield value is approximately equal to 552 MPa. It has many advantages such as high efficiency, safety, reliability, economy, single-phase, continuous, and environmental protection, and is an important method for long-distance transportation of oil and gas. An important development trend of oil and gas pipelines, especially natural gas pipelines, is long distance, large diameter, high pressure, and the selection of higher-grade steel pipes. The present invention aims at the high toughness problem of meeting the weld fracture toughness CTOD of 0.254 mm for the repair welding of basic low-hydrogen electrodes in X80 pipeline projects, and develops a high-strength and high-toughness X80 manual welding basic low-hydrogen electrode product for repair, and at the same time puts forward corresponding requirements for the alloy composition elements and production process of the product.

[0076] The present invention proposes a manufacturing method for a high-strength and high-toughness X80 manual welding basic low-hydrogen electrode for repair, as Figure 1 shown, which specifically includes the following steps:

[0077] S1: Determine the slag system of the basic low-hydrogen electrode according to the index requirements of the deposited metal of the basic low-hydrogen electrode and the mechanical property requirements of the girth weld joint using the basic low-hydrogen electrode. Specifically, the slag system of the coating can be determined by analyzing the alloy element burn-off and the transition of alloy components in the coating into the molten pool during the welding process, the degree of slag detachment during the welding process, and the weld joint property requirements. After adjustment and optimization, the alloy components of the deposited metal are as follows:

[0078] 0.065 wt% - 0.072 wt% C, 1.42 wt% - 1.50 wt% Mn, 0.28 wt% - 0.29 wt% Si, 0.0028 wt% - 0.0031 wt% S, 0.0045 wt% - 0.0064 wt% P, 2.31 wt% - 2.40 wt% Ni, and 0.14 wt% - 0.24 wt% Mo.

[0079] The index requirements of the deposited metal of the basic low-hydrogen electrode include the alloy components, mechanical properties, and diffusible hydrogen content index requirements of the deposited metal. Among them, the chemical composition alloy content, mechanical properties, and diffusible hydrogen content of the deposited metal need to meet the requirements specified in GBT32533-2016 high-strength steel electrodes.

[0080] The mechanical properties of the girth weld joint of the basic low-hydrogen electrode need to meet the technical regulations for onshore pipeline welding. In an embodiment of the present invention, the chemical composition and mechanical properties of the deposited metal are shown in Table 1 and Table 2 respectively:

[0081] Table 1 Chemical composition of the deposited metal (wt%)

[0082] Number C Si Mn P S Ni Mo V Cu 32005 0.072 0.29 1.50 0.0064 0.0028 2.40 0.24 0.0059 0.046

[0083] Table 2 Mechanical properties of the deposited metal

[0084]

[0085]

[0086] In another embodiment of the present invention, the chemical composition and mechanical properties of the deposited metal are shown in Table 3 and Table 4 respectively:

[0087] Table 3 Chemical composition of the deposited metal (wt%)

[0088] Number C Si Mn P S Ni Mo V Cu S21543 0.067 0.28 1.42 0.0045 0.0031 2.31 0.14 0.0062 0.021

[0089] Table 4 Mechanical properties of the deposited metal

[0090]

[0091] S2: Determine the composition index requirements, mechanical property requirements, and wire rod specifications for producing basic low-hydrogen electrodes, and remove the oxide scale from the determined wire rod, followed by drawing and wire cutting to form the welding core of the basic low-hydrogen electrode. Specifically, it includes the following steps: Remove the oxide scale on the surface of the wire rod by mechanical means;

[0092] Draw the wire rod with the oxide scale removed to a preliminary wire rod with the diameter required for the welding core;

[0093] Cut the preliminary wire rod into welding cores with standard lengths according to the requirements of GB / T32533.

[0094] It should be noted that the microscopic determination methods for the content of non-metallic inclusions in steel are basically the standard rating chart method and the corresponding image analysis method. The more commonly used standards are: GB / T 10561, ISO 4967, JIS G 0555. Among them, GB / T 10561 and JIS G 0555 are basically derived from ISO 4967, and are mainly applicable to rolled or forged steel with a compression ratio ≥ 3. This standard classifies non-metallic inclusions in steel into five categories: A, B, C, D, and DS. Among them, categories A to D are further divided into two categories for evaluation according to the thickness (based on diameter) of the inclusions, and the letter e is used to represent the inclusions in the coarse series. For each type of inclusion, the level increases from 0.5 to 3 levels with the content, with a level difference of 0.5 levels, for a total of 6 levels. The requirements for non-metallic slag inclusions and the index requirements for chemical compositions of the wire rod in this invention are shown in Table 5 and Table 6 respectively:

[0095] Table 5 Requirements for non-metallic slag inclusions in wire rod

[0096]

[0097] Table 6 Chemical composition of wire rod

[0098] (wt%) C Si Mn P S Ni Mo V Cu E19678 0.068 0.24 1.30 0.0053 0.0031 2.50 0.28 0.0058 0.028

[0099] S3: Determine the process parameters for producing the coating of the basic low-hydrogen electrode and prepare the basic low-hydrogen electrode according to the process parameters. Specifically, it includes powder mixing, powder conditioning, coating and pressing, and drying processes, including the following steps:

[0100] Mix the powder according to the coating slag system of the basic low-hydrogen electrode. Among them, the allowable errors for both single materials and total materials are within ±0.3%;

[0101] Condition the mixed powder. During the powder conditioning process, the dry mixing time of the powder is greater than or equal to 15 minutes, and the wet mixing time is 15 - 20 minutes;

[0102] After pre-treating the surface of the welding core, apply and press the conditioned powder onto the surface of the welding core. When applying and pressing, there is no oil stain on the surface of the welding core and the temperature is lower than 50°C;

[0103] Bake the coated and pressed welding core at a temperature of 350 - 400 °C to obtain the finished basic low-hydrogen electrode. The outer diameter tolerance of the finished electrode should be controlled within the range of -0.10 mm to +0.10 mm.

[0104] S4: Weld the test steel pipe with the manufactured basic low-hydrogen electrode and adjust the welding process parameters according to the existing on-site repair welding process specifications to determine the final welding process; the welding process parameters include but are not limited to welding current, interpass temperature, welding speed, welding position, etc. In an exemplary embodiment of the present invention, a wire rod with a diameter of 5.5 mm ± 0.1 mm is preliminarily drawn to the required diameter Φ4.0 mm of the welding core, and then cut into a standard length according to the requirements of GB / T32533 to prepare the basic low-hydrogen electrode as the welding core. The welding process parameters adopted in the experimental process are shown in Table 7:

[0105] Table 7 Welding process parameters

[0106] Welding current I (A) Welding speed v (cm / min) Interpass temperature (°C) Test condition Welding position 160 15-17 90-110 As-welded Flat position welding 150 7.5-9 140-150 As-welded Vertical position welding

[0107] In another exemplary embodiment of the present invention, a wire rod with a diameter of 5.5 mm ± 0.1 mm is preliminarily drawn to the required diameter Φ3.2 mm of the welding core, and then cut into a standard length according to the requirements of GB / T32533 to prepare the basic low-hydrogen electrode as the welding core. The welding process parameters adopted in the experimental process are shown in Table 8:

[0108] Table 8 Welding process parameters

[0109] Welding current I (A) Welding speed v (cm / min) Interpass temperature (°C) Test condition Welding position 120 14-15 90-110 As-welded Flat position welding 115 7.5-8.5 140-150 As-welded Vertical position welding

[0110] Adjust the welding process parameters according to the existing on-site repair welding process specifications to determine the final welding process, including the following steps:

[0111] Determine the welding process parameters that need to be adjusted. The welding process parameters include welding current, welding speed, interpass temperature, and welding position;

[0112] Examine the welding processability of the basic low-hydrogen electrode. The examination indicators include the effects on arc stability, arc appearance, droplet transfer state, molten pool fluidity, wire feeding stability, spatter and bead appearance, as well as molten metal fluidity and spreading, fume volume, slag detachment, arc blow, etc.

[0113] Compare the surface formation of flat welding, horizontal welding, vertical welding, and overhead welding under different welding currents in the laboratory and the mechanical properties of the deposited metal after welding;

[0114] Determine the final welding process according to the examination results of the welding processability and the mechanical properties of the deposited metal at the welding position under different welding currents.

[0115] S5: Evaluate the final welding process; specifically including the following steps:

[0116] Use the adjusted on-site repair welding process parameters to perform circumferential welds on the steel pipe to be tested. After passing the non-destructive testing, cut and machine the circumferential weld tensile specimens, circumferential weld hardness test specimens along the wall thickness direction, impact toughness specimens at different positions of the weld and fusion line, and CTOD specimens at different positions of the fusion line and heat-affected zone, and perform tensile property tests on the transverse plate specimens of the circumferential weld. Record the fracture position. If the fracture occurs on the base metal and the tensile strength is greater than or equal to 95% of the nominal strength of the pipe material, it is judged as qualified. If the fracture occurs on the weld and the tensile strength is greater than or equal to the nominal strength of the pipe material, it is judged as qualified.

[0117] In some embodiments of the present invention, the basic low-hydrogen electrodes welded with different welding process parameters are respectively as Figure 2-7 shown Figure 2 is the flat position welding appearance diagram with a current of 150A. Under the condition of welding current I = 150A, the arc is stable, the spatter is small, the slag removal is good, and the weld formation is good; Figure 3 is the flat position welding appearance diagram with a current of 170A. Under the condition of welding current I = 170A, the arc is stable, the spatter is small, the slag removal is good, and the weld formation is good; Figure 4 is the flat position welding appearance diagram with a current of 190A. Under the condition of welding current I = 190A, the arc is stable, there is small particle spatter, the slag removal is good, and the weld formation is good; Figure 5 is the circumferential weld formation diagram with a current of 150A. When the welding current of 150A is used for horizontal fillet welding, the arc is stable, the spatter is small, the slag removal is good, and the fillet weld fusion is good; Figure 6 is the fillet weld formation diagram with a current of 150A. When the welding current of 150A is used for overhead fillet welding, the arc is stable, the spatter is small, the slag removal is good, and the fillet weld fusion is good; Figure 7 is the vertical fillet weld formation diagram with a current of 150A.

[0118] After performing welding process qualification on the full-automatic welding, it is found that the performance indicators satisfied by its welds are as follows:

[0119] 1) The tensile strength of the circumferential weld joint should not be lower than 625 MPa, and the tensile strength of the weld round bar specimen is equivalent to the strength of the pipe material; in an embodiment of the present invention, the tensile diagram of the weld round bar specimen is as Figure 8 shown, where a) is the size requirement of the transverse tensile specimen of the welded joint, b) is the sampling schematic diagram of the all-weld metal tensile specimen, and c) is the size requirement of the all-weld metal tensile specimen;

[0120] 2) The CTOD test values of the fracture toughness of its weld seam and heat-affected zone meet the requirement of ≥ 0.254 mm. The notch positions of CTOD at the weld center and in the heat-affected zone are as Figure 9 shown;

[0121] 3) The hardness values of the weld metal and heat-affected zone of the girth weld joint: the root pass shall not be greater than 300 HV 10 , and the rest shall not be greater than 325 HV 10 ;

[0122] The single value of the -20 °C Charpy impact toughness of the girth weld joint shall not be lower than 38 J, and the average value shall not be lower than 50 J.

[0123] Prepare a basic low-hydrogen electrode for manual welding of high-strength and high-toughness X80 for repair welding according to the above method, and perform on-site welding in the X80 pipeline project. The alloy composition of the low-hydrogen electrode, the process performance of on-site welding, and the mechanical property test of the completed weld are respectively evaluated.

[0124] Step 1: Carry out steel smelting of wire rods according to the chemical composition of the provided low-hydrogen electrode core to obtain wire rods with a diameter of 5.5 mm, determine the slag system of the coating, and cut them into standard lengths according to the requirements of GB / T 32533 for use as electrode cores.

[0125] Step 2: Determine the powder blending process, powder mixing, coating and drying processes for producing the coating of the basic low-hydrogen electrode, and use the determined coating slag system and electrode core to manufacture the basic low-hydrogen electrode.

[0126] In this embodiment, the allowable error of powder blending is controlled within ±0.5 kg; during powder mixing, the dry mixing time of the powder product shall be ≥ 15 minutes, and the wet mixing time shall be 15 - 20 minutes; during powder coating, the surface of the electrode core shall be pretreated first to remove surface oil stains and the temperature shall be lower than 50 °C; the baking temperature is 350 - 400 °C, and the outer diameter tolerance of the finished electrode shall be controlled within the range of -0.10 mm to +0.10 mm.

[0127] Step 3: Adjust the on-site repair welding process parameters according to the existing on-site repair welding process specifications. Some evaluation indexes of the girth welding process performance of the domestic X80-class basic low-hydrogen electrode in this embodiment are shown in Table 9:

[0128] Table 9 Evaluation Indexes of Girth Welding Process Performance of Domestic X80-Class Solid Basic Low-Hydrogen Electrodes

[0129]

[0130] Step 4: After welding the girth weld of the test steel pipe and passing the non-destructive inspection, conduct mechanical property inspection of the weld. The detailed inspection process is as follows:

[0131] (1) According to Figure 10Samples are taken from the indicated sampling positions for tensile, back bend or side bend, notched hammer break, surface finish or side bend, impact test, and macro metallographic sampling of the circumferential weld and / or weld joint of the welded test steel pipe respectively;

[0132] Tensile property tests are carried out on the weld joint and the full weld according to GB / T 228.1-2021. The tensile stress-strain curves of the full weld samples T0-WM and T6-WM are as Figure 11 shown. T1 and T2 are weld joint samples, and the tensile test results of the weld joint are shown in Table 10;

[0133] Table 10 Tensile Test Results

[0134]

[0135]

[0136] In the table, DEC-OGP-G-WD-002-2020-1 is the "Technical Regulations for Line Welding of Oil and Gas Pipeline Engineering".

[0137] (2) Charpy impact tests are carried out according to GB / T 229-2020 to determine the notch sensitivity of the circumferential weld metal material of the steel pipe to be tested. The results are shown in Table 11:

[0138] Table 11 Charpy Impact Test Results

[0139]

[0140] (3) Notched hammer break tests are carried out according to the standard GB / T 31032-2014. The test results are shown in Table 12:

[0141] Table 12 Notched Hammer Break Test Results

[0142]

[0143]

[0144] (4) Guided bend tests are carried out according to the standard GB / T 2653-2008. The results are shown in Table 13:

[0145] Table 13 Guided Bend Test Results

[0146]

[0147] (5) Vickers hardness tests are carried out according to the standard GB / T 4340.1-2009. The results are shown in Table 14, and the indentation positions are as Figure 12 shown;

[0148] Table 14 Vickers Hardness Test Results (HV10)

[0149]

[0150]

[0151] (6) Metallographic analysis was carried out according to the standard GB / T 13298-2015, and the results are shown in Table 15. The macroscopic morphology is as Figure 13 and 14 shown, where Figure 13 is the macroscopic morphology diagram of the weld joint 1#M2 (repaired weld), Figure 14 is the macroscopic morphology diagram of the weld joint 2#M2 (repaired weld);

[0152] Table 15 Results of macro-examination of welds

[0153]

[0154] (7) Fracture toughness (CTOD) test

[0155] The yield strength and tensile strength of the specimen material at the test temperature are respectively: yield strength R p0.2 = 744 MPa; tensile strength R m = 807 MPa. The Poisson's ratio is taken as 0.3 and the elastic modulus E = 210 GPa during the calculation process. One specimen is taken from the weld and heat-affected zone at the flat position, vertical position and overhead position of the weld joint respectively. The specimen is a three-point bending specimen with a nominal size of W = 36 mm and B = 18 mm. An integral knife-edge specimen is used, that is, Z = 0. The prefabricated fatigue crack data are shown in Table 16.

[0156] Table 16 Prefabricated crack data

[0157]

[0158]

[0159] The test was carried out according to the standard GB / T 21143-2014, the loading speed was 1 mm / min, the COD gauge model for monitoring the crack mouth opening displacement was 3541-005M-100M-ST; the measurement of the crack length was carried out using a fracture analyzer with a measurement accuracy of 0.001 mm. The measurement results of the crack size are shown in Table 17.

[0160] Table 17 Measurement results of crack size

[0161]

[0162] The CTOD test results are shown in Table 18:

[0163] Table 18 Fracture toughness (CTOD) test results

[0164]

[0165]

[0166] CTOD values in Table 18 (1) Calculated according to Formula (19) of GB / T 21143-2014 standard, CTOD values (2) Calculated according to Formula (7) of ISO15653-2018 standard.

[0167] The verification of the result validity is shown in Table 19. The test curves and fracture morphologies of the above 12 specimens are as Figure 15 to Figure 26 shown.

[0168] Verification of result validity in Table 19 (according to Article 8.3.6 of GB / T21143-2014 standard)

[0169]

[0170]

[0171] 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 described 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 manufacturing method of an alkaline low-hydrogen electrode for manual welding of X80 for repair welding, characterized in that, The method includes the following steps: Determine the coating slag system of the basic low-hydrogen electrode according to the index requirements of the deposited metal of the basic low-hydrogen electrode and the mechanical property requirements of the girth weld joint using the basic low-hydrogen electrode. Determine the composition, mechanical property requirements and wire rod specifications of the wire rod required for producing the basic low-hydrogen electrode, and remove the oxide scale from the determined wire rod, draw and cut it into the welding core of the basic low-hydrogen electrode. Determine the process parameters for producing the coating of the basic low-hydrogen electrode and manufacture the basic low-hydrogen electrode according to the process parameters. Weld the test steel pipe with the manufactured basic low-hydrogen electrode and adjust the welding process parameters according to the existing on-site repair welding process regulations to determine the final welding process.

2. The manufacturing method of the alkaline low-hydrogen electrode for manual welding of X80 for repair welding according to claim 1, wherein the index requirements of the deposited metal of the alkaline low-hydrogen electrode include the alloy composition and mechanical properties of the deposited metal; Among them, The chemical composition alloy content and mechanical properties of the deposited metal shall meet the requirements of GBT32533-2016 high-strength steel electrodes. The mechanical properties of the girth weld joint of the basic low-hydrogen electrode shall meet the requirements of the welding technology regulations for oil and gas pipeline engineering lines.

3. The manufacturing method of the alkaline low-hydrogen electrode for manual welding of X80 for repair welding according to claim 1, characterized in that, The coating slag system of the basic low-hydrogen electrode is calcium oxide - fluoride - silica - titanium dioxide. The alloy composition of the deposited metal is as follows: 0.065wt% - 0.072wt% C, 1.42wt% - 1.50wt% Mn, 0.28wt% - 0.29wt% Si, 0.0028wt% - 0.0031wt% S, 0.0045wt% - 0.0064wt% P, 2.31wt% - 2.40wt% Ni and 0.14wt% - 0.24wt% Mo.

4. The manufacturing method of the alkaline low-hydrogen electrode for manual welding of X80 for repair welding according to claim 1, characterized in that, The composition of the wire rod required for producing the basic low-hydrogen electrode includes alloy components and non-metallic inclusions; among them, the alloy components of the wire rod include: 0.068wt% C, 0.24wt% Si, 1.30wt% Mn, 0.0053wt% P, 0.0031wt% S, 2.50wt% Ni, 0.28wt% Mo, 0.0058wt% V and 0.028wt% Cu. The non-metallic inclusions in the wire rod include: The fine series of type A inclusions is less than or equal to 1.5, and the coarse series is less than or equal to 1; the fine series of type B inclusions is less than or equal to 1.5, and the coarse series is less than or equal to 1; the fine series of type C inclusions is less than or equal to 1.0, and the coarse series is less than or equal to 0.5; the fine series of type D inclusions is less than or equal to 1.5, and the coarse series is less than or equal to 1.0; the DS type inclusions are less than or equal to 1.

5.

5. The manufacturing method of the alkaline low-hydrogen electrode for manual welding of X80 for repair welding according to claim 1, characterized in that, The specific steps of removing the oxide scale from the determined wire rod, drawing and cutting it into the welding core of the basic low-hydrogen electrode include the following steps: Remove the oxide scale on the surface of the wire rod by mechanical method. Draw the wire rod with the oxide scale removed to the preliminary wire rod with the diameter required for the welding core. Cut the preliminary wire rod into the welding core with a standard length according to the requirements of GB / T32533.

6. The manufacturing method of the alkaline low-hydrogen electrode for manual welding of X80 for repair welding according to claim 5, characterized in that, Determine the preparation process parameters for producing the coating of the basic low-hydrogen electrode and manufacture the basic low-hydrogen electrode according to the preparation process parameters specifically include: Mix the powder according to the coating slag system of the basic low-hydrogen electrode, and the allowable error of the single material and the total material is between ±0.3%. Mix the prepared powder materials, and during the powder mixing process, the dry mixing time of the powder materials shall be greater than or equal to 15 minutes, and the wet mixing time shall be 15 - 20 minutes; After pre - treating the surface of the welding core, apply and press the mixed powder materials onto the surface of the welding core. When applying and pressing, there shall be no oil stain on the surface of the welding core and the temperature shall be lower than 50 °C; Bake the welding core with the applied and pressed powder at a temperature of 350 - 400 °C to obtain the finished basic low - hydrogen welding electrode.

7. The manufacturing method of the alkaline low-hydrogen electrode for manual welding of X80 for repair welding according to claim 1, characterized in that, Adjust the welding process parameters according to the existing on - site repair welding process regulations. Determining the final welding process parameters includes the following steps: Determine the welding process parameters that need to be adjusted. The welding process parameters include welding current, welding speed, inter - pass temperature, and welding position; Examine the welding processability of the basic low - hydrogen welding electrode. The examination indicators include arc stability, arc appearance, droplet transfer state, molten pool fluidity, wire feeding stability, spatter, and forming appearance; Compare the surface forming of flat welding, horizontal welding, vertical welding, and overhead welding under different welding currents and the mechanical properties of the deposited metal after welding in the laboratory; Determine the final welding process based on the results of the examination of welding processability and the mechanical properties of the deposited metal at the welding position under different welding currents.

8. The manufacturing method of the basic low-hydrogen electrode for X80 manual welding for repair, characterized in that, The manufacturing method further includes evaluating the final welding process after determining the final welding process.

9. The manufacturing method of the basic low-hydrogen electrode for X80 manual welding for repair according to claim 8, characterized in that, The evaluation of the final welding process includes: Weld the circumferential weld of the test steel pipe according to the final welding process using the basic low - hydrogen welding electrode and conduct non - destructive testing; If the non - destructive testing of the circumferential weld of the test steel pipe is qualified, then cut and machine the tensile test specimen of the circumferential weld, the hardness test specimen of the circumferential weld along the wall thickness direction, the impact toughness specimens at different positions of the weld and the fusion line, and the CTOD specimens at different positions of the fusion line and the heat - affected zone; Conduct tensile property testing on the processed circumferential weld and record the fracture position; if the fracture position is on the base metal and the tensile strength is greater than or equal to 95% of the nominal strength of the pipe material, it is judged as qualified; if the fracture position is on the weld and the tensile strength is greater than or equal to the nominal strength of the pipe material, it is judged as qualified.

10. A basic low-hydrogen electrode for X80 manual welding for repair, characterized in that, Manufactured by the method according to any one of claims 1 - 9.

11. The basic low-hydrogen electrode for X80 manual welding for repair according to claim 10, characterized in that, The circumferential weld joint formed by using the basic low - hydrogen welding electrode for repair welding has the following characteristics: The tensile strength of the repair weld is not less than 625 MPa; The fracture toughness test values of the weld and the heat - affected zone are greater than or equal to 0.254 mm; The hardness value of the weld metal and the heat-affected zone of the repaired weld is less than or equal to 300 HV for the root pass 10 , and the hardness of the remaining areas is less than or equal to 325 HV 10 ; The single - value of the - 20 °C Charpy impact toughness of the repair weld is not less than 38 J, and the average value is not less than 50 J.

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