Large-diameter medium-chromium alloy high-frequency welded pipe and processing method

Abstract

The present application belongs to the technical field of petroleum pipes, and particularly relates to a large-diameter medium-Cr alloy high-frequency welded pipe and a processing method. The large-diameter medium-Cr alloy high-frequency welded pipe has a chemical composition according to mass percentage of C: ≤0.10%, Si: ≤0.50%, Mn: ≤2.0%, P: ≤0.020%, S: ≤0.005%, Cr: 1.0-10.0%, Ni: ≤5.0%, Cu: ≤2.0%, Mo: ≤2.0%, Nb+V+Ti: ≤0.15%, and the rest is iron and inevitable impurities. The yield strength of the large-diameter medium-Cr alloy high-frequency welded pipe is ≥360 MPa, the pipe diameter is 168-660 mm, and the wall thickness is ≤25.4 mm. The welded pipe has high weld strength and toughness, excellent corrosion resistance, and good economy. The processing method can realize full-dimensional protection effect before and after and above and below the high-frequency welding area of the existing welding unit, has small gas consumption, good gas airtightness, high weld quality, and is suitable for high-quality welding production of the large-diameter 168-660 mm medium-Cr alloy high-frequency welded pipe.

Description

Technical Field

[0001] This invention belongs to the field of petroleum pipe technology, and specifically relates to a large-diameter high-frequency welded pipe with medium Cr alloy and its processing method. Background Technology

[0002] Currently, high-frequency welding of stainless steel is mainly used to produce thin-walled stainless steel straight seam welded pipes. Due to weld quality issues, its primary applications are decorative pipe fittings and non-pressure or low-pressure pipelines. High-frequency welding processes and technologies for thick-walled and pressure-bearing alloy pipes are still under continuous research. In recent years, studies have found that adding a small amount of Cr to steel can reduce its corrosion rate. The corrosion rate of 3% Cr steel is more than twice that of ordinary carbon steel. When the Cr content in steel gradually increases to 10%, the resistance to CO2 corrosion is significantly enhanced, and it can effectively inhibit the occurrence of localized corrosion. 13Cr, super 13Cr, duplex stainless steel, and nickel-based alloys are widely used in CO2 and CO2 / H2S corrosion control. However, the initial investment for using alloy steels with more than 13% Cr or nickel-based alloys is too high, resulting in low economic efficiency and a low investment ratio for use in low-yield oil and gas fields. In the oil and gas extraction and chemical industries, the development of 1-10% Cr alloy high-frequency welded pipes, which offer both corrosion resistance and cost-effectiveness, can compensate for the poor corrosion resistance and high cost of carbon steel and stainless steel.

[0003] Because high-alloy steel contains 1-10% Cr and other alloying elements, an oxide layer forms on the weld surface of the plate during high-frequency welding of ordinary large-diameter high-frequency welded pipes. During forming under the pressure of the vertical and side extrusion rollers, the generated oxides cannot be squeezed out of the weld fusion surface, remaining at the fusion line. During subsequent solidification, oxide inclusions form in the weld area, resulting in large areas of incomplete fusion, incomplete penetration, and inclusions, making it impossible to guarantee weld quality. Compared to carbon steel coils, high-alloy steel coils have higher resistivity, a larger coefficient of linear expansion, and lower thermal conductivity, requiring new forming, welding process parameters, and heat treatment processes. For small-diameter, thin-walled high-alloy steel high-frequency welded pipes with a diameter of less than 150mm and a wall thickness of less than 7mm, the welding speed can even far exceed 30m / min. This high welding speed reduces the chance of the weld reacting with oxygen in the air or water, reducing the formation of inclusions and cracks, thus improving weld quality to some extent. A very small number of companies have innovatively designed and manufactured large-scale enclosures for welding medium and high alloy high-frequency welded pipes. These enclosures enclose the vertical rollers, side extrusion rollers, welding frame, and pipe within a huge enclosure. The enclosure is filled with protective gas during welding. However, the enclosures are complex, costly, and consume a lot of gas. This method is generally limited to the production of alloy steel pipes with a diameter of less than 300mm. Due to the large size of the large-diameter welded pipe unit itself, and the compact size of the unit's resistance induction system, internal and external burr removal, and heat treatment devices, it is currently impossible to effectively achieve protective welding of larger diameter alloy pipes.

[0004] The publication number CN104999277 A, published in 2015, is titled "Production Method of Corrosion-resistant and Wear-resistant Stainless Steel High-frequency Welded Pipe with Outer Diameter of 108~660.4mm". It only has one inner protective gas pipe and no outer protective device, which cannot effectively protect the outer weld seam of the welded pipe and the weld seam of thick-walled welded pipes, resulting in unstable weld quality. Summary of the Invention

[0005] To address the aforementioned problems, the purpose of this invention is to provide a large-diameter medium-Cr alloy high-frequency welded pipe and its processing method. This welded pipe exhibits high weld strength and toughness, excellent corrosion resistance, and good economic efficiency. This invention can achieve all-round three-dimensional protection in the confined space of existing welding units, covering the front, back, top, and bottom of the high-frequency welding area. It consumes less gas, has good gas tightness, and produces high-quality welds. Combined with the pipe manufacturing process, it is suitable for high-quality welding production of large-diameter 168-660mm medium-Cr alloy high-frequency welded pipes.

[0006] The technical solution of the present invention is: a large-diameter high-frequency welded pipe of medium-Cr alloy, wherein the chemical composition of the large-diameter high-frequency welded pipe of medium-Cr alloy is as follows by mass percentage: C: ≤0.10%, Si: ≤0.50%, Mn: ≤2.0%, P: ≤0.020%, S: ≤0.005%, Cr: 1.0~10.0%, Ni: ≤5.0%, Cu: ≤2.0%, Mo: ≤2.0%, Nb+V+Ti: ≤0.15%, with the remainder being iron and unavoidable impurities.

[0007] The large-diameter Cr alloy high-frequency welded pipe has a yield strength ≥360MPa, a pipe diameter of 168-660mm, and a wall thickness ≤25.4mm.

[0008] A method for processing a large-diameter high-frequency welded pipe with medium Cr alloy, comprising the following steps:

[0009] S1: Uncoiling and welding: Align the head and tail of the Cr alloy coil with the joint.

[0010] S2: Edge planing: Planing the width of the Cr alloy coil plate by ±0.20mm;

[0011] S3: Forming: During the Cr alloy coil forming process, the extrusion amount is adjusted to 6±0.5mm and the sizing amount is 6.0±0.5mm; during the welding forming, hollow vertical rollers and hollow side extrusion rollers made of high temperature resistant Cr-Mo material are used, and cooling circulating water is injected into the hollow vertical rollers and hollow side extrusion rollers for cooling.

[0012] S4: inner and outer gas protection high frequency welding: when high frequency induction resistance welding is adopted, inner and outer gas protection devices are adopted, the outer gas protection device is connected with 99.9% high purity argon, the inner gas protection device is connected with 99.9% high purity nitrogen, the high frequency welding induction welding frequency of the large diameter Cr alloy plate is 350±20KHZ, and the welding speed is 18±3m / min;

[0013] S5: normalizing heat treatment: the temperature is 910±20℃;

[0014] S6: aging heat treatment: the whole pipe body is heated to 500-550℃, and the aging treatment is performed for 20-60min;

[0015] S7: sizing flying shear: the high frequency welded pipe is cut according to the designed length;

[0016] S8: straightening;

[0017] S9: X-ray inspection and ultrasonic inspection;

[0018] S10: pipe end beveling processing;

[0019] S11: appearance size inspection;

[0020] S12: physical and chemical and corrosion resistance performance test: according to the test batch, the chemical composition analysis, charpy impact, flattening, tensile and corrosion test of the large diameter Cr alloy high frequency welded pipe are performed, so that the physical and chemical properties and the corrosion resistance of the welded pipe meet the requirements of API SPEC 5L standard and working condition corrosion respectively, and the large diameter Cr alloy high frequency welded pipe processing is completed.

[0021] In the step S4, the inner gas protection device is located in the welded pipe and includes two high-temperature-resistant gas hole pipes arranged on the resistance welding core rod and parallel to the axis of the welded pipe, one end of the high-temperature-resistant gas hole pipe is provided with an inner protection gas inlet, and the other end is closed, a plurality of inner protection gas outlets are arranged on the outer side of the closed end of the high-temperature-resistant gas hole pipe, and the two sides of the inner protection gas outlet are respectively provided with a first high-temperature-resistant sealing gas curtain and a second high-temperature-resistant sealing gas curtain.

[0022] The first and second high-temperature-resistant sealing gas curtains are circular flexible fiber sealing gas curtains, the thickness of the first and second high-temperature-resistant sealing gas curtains ranges from 20 to 50 mm, the first and second high-temperature-resistant sealing gas curtains have an inner square and outer circle structure, the first and second high-temperature-resistant sealing gas curtains are respectively sleeved on the resistance welding mandrels before and after the welding area, the first and second high-temperature-resistant sealing gas curtains and the resistance welding mandrels are respectively fixed or filled with heat-resistant glue or high-temperature-resistant cotton, the heat-resistant glue is polytetrafluoroethylene heat-resistant glue, the high-temperature-resistant cotton is polycrystalline molybdenum high-temperature-resistant cotton, the first high-temperature-resistant sealing gas curtain is provided with an inner burr scraper at the front end, the outer surface of the welded pipe at the position of the second high-temperature-resistant sealing gas curtain is provided with a high-temperature-resistant fiber paving blanket, the high-temperature-resistant fiber paving blanket is trapezoidal, the material of the high-temperature-resistant fiber paving blanket is zirconium-containing ceramic aluminum silicate, the high-temperature-resistant gas hole pipe can resist a temperature above 1600 DEG C, the inner protective gas outlet has a hole diameter ranging from 2 to 5 mm, a hole spacing ranging from 2 to 4 mm, and a total length ranging from 20 to 40 mm.

[0023] In the step S4, the pipe outer gas protection device is located above the top of the welded pipe outside and has a "Y" type high-temperature-resistant non-magnetic box body, a plurality of outer protective gas inlets are arranged on the upper part of the high-temperature-resistant non-magnetic box body, and a plurality of outer protective gas outlets are arranged on the lower part of the high-temperature-resistant non-magnetic box body, and the outer protective gas outlets are provided with heat-resistant sealing adhesive tape ear curtains between the outer protective gas outlets and the welded pipe.

[0024] The pipe outer gas protection device comprises a high-temperature-resistant non-magnetic left block body, a high-temperature-resistant non-magnetic middle block body and a high-temperature-resistant non-magnetic right block body connected in sequence, the high-temperature-resistant non-magnetic middle block body is parallel to the welding seam direction of the welded pipe, the included angle of the high-temperature-resistant non-magnetic left block body and the high-temperature-resistant non-magnetic right block body is the same as the joint angle of the strip steel before welding, a plurality of outer protective gas inlets are arranged on the upper part of the high-temperature-resistant non-magnetic left block body, the high-temperature-resistant non-magnetic middle block body and the high-temperature-resistant non-magnetic right block body, a plurality of outer protective gas outlets are arranged on the lower part of the high-temperature-resistant non-magnetic left block body, the high-temperature-resistant non-magnetic middle block body and the high-temperature-resistant non-magnetic right block body, the outer protective gas outlet has a hole diameter ranging from 2 to 3 mm, the "Y" type high-temperature-resistant non-magnetic box body is fixed on the welded pipe outside the welding seam by a support, the protective gas outlet of the non-magnetic box body is aligned with the welding seam bite point, the bottom of the non-magnetic box body is 20-50 mm away from the welded pipe welding seam, the material of the high-temperature-resistant gas hole pipe is 99 corundum, and the material of the "Y" type high-temperature-resistant non-magnetic box body is 6061 aluminum alloy.

[0025] In the step S4, the inner and outer gas protection high-frequency welding specifically comprises the following steps:

[0026] S41: The tube internal gas protection device is placed in the welding area inside the welded tube, and the tube external gas protection device is placed above the welding area outside the welded tube;

[0027] S42: When producing the high-frequency welded welded tube of medium-high alloy, nitrogen or argon is introduced into the internal protection gas inlet, and the external protection "Y" type high-temperature resistant non-magnetic box body is introduced into appropriate argon through the external protection gas inlet, and the internal and external protection simultaneously plays a gas protection role, so that the large-diameter medium-Cr alloy plate high-frequency welding can be completed in the environment of isolating air and water.

[0028] The technical effects of the present application are: 1. The Cr content of the large-diameter medium-Cr alloy high-frequency welded welded tube is 1.0-10.0%, and Cr is the most effective element for resisting CO2 corrosion, which can quickly form a dense and extremely thin Cr2O3 passivation film on the metal surface. By further adding alloy elements such as Ni, Mo or Cu, the critical temperature and sulfide stress corrosion resistance of CO2 corrosion resistance can be further improved, which can make up for the poor corrosion resistance of carbon steel and the high cost of stainless steel; 2. When the welded tube is formed and welded, the large-diameter medium-Cr alloy high-frequency welded welded tube is welded in the water-free forming mode and the internal and external gas protection state, which isolates the oxygen in the cooling water and the oxygen in the air, greatly ensures that the alloy elements in the weld are not oxidized and no inclusions and cracks are formed, and the weld formed on both sides of the alloy coil plate can be welded together without defects; 3. The hollow vertical roller and hollow side extrusion roller made of Cr-Mo material are injected with cooling circulating water, which greatly reduces the high heat generated by the mutual extrusion transmission of the vertical roller and the side extrusion roller and the welded tube, and reduces the friction burn of the roller and the steel pipe; 4. The internal and external gas protection devices can be flexibly disassembled, and can realize high-frequency welding of medium-high alloy steel pipe when assembled, and can realize high-frequency welding of ordinary carbon steel pipe when disassembled. The internal and external gas protection devices can be flexibly designed according to the small space of the existing large-diameter high-frequency welded welded tube unit, can realize full-dimensional protection effect before and after the welding area and up and down, the gas consumption is small, the airtightness is good, and the welded tube and the thick-walled welded tube can be effectively protected, and the welded tube has no any oxidation defect after gas protection; 5. The welded joint is subjected to normalizing heat treatment at 910±20 DEG C which is lower than that of carbon steel pipe, the whole pipe body is heated to 500 DEG C-550 DEG C, and the aging treatment is 20-60 min, which can ensure that the weld has high toughness without changing the strength and yield ratio of the pipe body. At the same time, for the large-diameter medium-Cr alloy high-frequency welded welded tube, a high-temperature and high-pressure kettle corrosion test is carried out under multiple CO2 and bacterial corrosion conditions, and after soaking for 7-15 days, the corrosion point corrosion depth of the medium-Cr welded tube body and the welded joint is lower than that of the same steel grade carbon steel sample, and the average corrosion rate is far lower than that of the same steel grade carbon steel sample. The medium-Cr alloy high-frequency welded welded tube has excellent mechanical and corrosion resistance comprehensive performance and good economy.

[0029] The following will be further described with reference to the accompanying drawings. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 This is a schematic diagram of the internal and external gas protection device for processing large-diameter medium-Cr alloy high-frequency welded pipes according to an embodiment of the present invention.

[0031] Figure 2 Low-magnification metallographic microstructure of a weld seam without internal or external gas protection devices.

[0032] Figure 3 Low-magnification metallographic microstructure of the weld seam with internal and external gas protection devices.

[0033] Figure 4 High-magnification metallographic microstructure of the weld seam with internal and external gas protection devices.

[0034] Reference numerals: 1-Welded pipe, 2-High temperature resistant vent pipe, 3-Inner protective gas inlet, 4-Inner protective gas outlet, 5-First high temperature resistant sealing gas curtain, 6-Second high temperature resistant sealing gas curtain, 7-High temperature resistant non-magnetic left block, 8-High temperature resistant non-magnetic middle block, 9-High temperature resistant non-magnetic right block, 10-Outer protective gas inlet, 11-Outer protective gas outlet, 12-Heat resistant sealing tape ear curtain, 13-High temperature resistant fiber covering blanket, 14-Resistance welding core rod, 15-Inner deburring scraper. Detailed Implementation

[0035] Example 1

[0036] like Figure 1 As shown, a large-diameter high-frequency welded pipe with medium Cr alloy is disclosed. The chemical composition of the large-diameter high-frequency welded pipe with medium Cr alloy is as follows by mass percentage: C: ≤0.10%, Si: ≤0.50%, Mn: ≤2.0%, P: ≤0.020%, S: ≤0.005%, Cr: 1.0~10.0%, Ni: ≤5.0%, Cu: ≤2.0%, Mo: ≤2.0%, Nb+V+Ti: ≤0.15%, with the remainder being iron and unavoidable impurities.

[0037] In the composition design of large-diameter Cr alloy high-frequency welded pipes: Cr is added to the steel to increase its corrosion resistance. The Cr content is closely related to the CO2 partial pressure and temperature in oil and gas transportation. Cr is the most effective element against CO2 corrosion, and it can quickly form a dense and extremely thin Cr2O3 passivation film on the metal surface. With the increase of Cr content, the CO2 corrosion resistance is significantly enhanced, and the degree of reduction in corrosion rate is greater. By further adding alloying elements such as Ni, Mo, or Cu, the critical temperature for CO2 corrosion application and the resistance to sulfide stress corrosion can be further improved. The Cr content in conventional stainless steel is at least 10.5%. As an economical large-diameter 1.0-10.0% Cr and other alloy high-frequency welded pipe, the weld mechanical properties are good.

[0038] The yield strength of the large-diameter medium Cr alloy high-frequency welded pipe is greater than or equal to 360 MPa, the pipe diameter is 168-660 mm, and the wall thickness is less than or equal to 25.4 mm.

[0039] A processing method of a large-diameter medium Cr alloy high-frequency welded pipe, processing a large-diameter medium Cr alloy high-frequency welded pipe as described above, comprising the following steps:

[0040] S1: butt welding: butt joint of the head and tail of the medium Cr alloy coil plate is flush;

[0041] S2: edge planing: the width of the medium Cr alloy coil plate is planed by ±0.20 mm;

[0042] S3: forming: adjusting the extrusion amount of 6±0.5 mm and the sizing amount of 6.0±0.5 mm in the process of arranging and rolling the medium Cr alloy coil plate; when welding and forming, the hollow vertical roller and hollow side extrusion roller made of high-temperature resistant Cr-Mo material are used, and cooling circulating water is injected into the hollow vertical roller and hollow side extrusion roller for cooling;

[0043] S4: internal and external gas protection high-frequency welding: when using high-frequency induction resistance welding, the internal and external gas protection devices are used, the external gas protection device is connected with high-purity argon with a volume fraction of 99.9%, and the internal gas protection device is connected with high-purity nitrogen with a volume fraction of 99.9%; the high-frequency induction welding frequency of the large-diameter medium Cr alloy plate is 350±20 KHZ, and the welding speed is 18±3 m / min;

[0044] S5: normalizing heat treatment: the temperature is 910±20℃;

[0045] S6: aging heat treatment: heating the whole pipe body to 500-550℃ and aging for 20-60 min;

[0046] S7: sizing flying shear: cutting the high-frequency welded pipe according to the designed length;

[0047] S8: straightening;

[0048] S9: X-ray inspection and ultrasonic inspection;

[0049] S10: pipe end beveling processing;

[0050] S11: appearance size inspection;

[0051] S12: physical and chemical properties and corrosion resistance test: chemical composition analysis, charpy impact, flattening, tensile and corrosion test of the large-diameter medium Cr alloy high-frequency welded pipe are carried out according to the test batch, to ensure that the physical and chemical properties and corrosion resistance of the welded pipe meet the requirements of API SPEC 5L standard and working condition corrosion respectively, and the processing of the large-diameter medium Cr alloy high-frequency welded pipe is completed.

[0052] In the step S3 forming process, because the elastic modulus of the medium Cr alloy coil sheet is slightly lower than that of the ordinary carbon steel, according to the actual strength, high resistivity and low thermal conductivity of the medium Cr alloy coil sheet, the characteristics of the roll involute in the roll forming process and the tension effect when the roll is formed are used to adjust the roll parameters and working plate width of the rough forming rack, the extrusion force is greatly increased in the forming process of the medium Cr alloy coil sheet, the extrusion amount is adjusted to 6±0.5mm according to the extrusion amount and the longitudinal diameter, and the sizing amount is adjusted to 6.0±0.5mm, so as to control the residual stress in the forming stage and ensure that the high-frequency welded pipe has good ovality and low residual stress after forming. In the welding stage, the cooling device for the outer pipe is cancelled, and the hollow vertical roll and hollow side extrusion roll made of high-temperature Cr-Mo material are used to inject cooling circulating water into the hollow vertical roll and hollow side extrusion roll for cooling, so as to reduce the high heat generated by the vertical roll and side extrusion roll when extruding and transmitting the pipe, ensure that the roll and pipe are not burned, and most importantly, achieve the high-frequency welding effect of the weld joint area without water and oxygen, and ensure the high-quality welding of the weld joint under the condition of no oxygen.

[0053] In the step S4, the pipe internal gas protection device is located in the welded pipe 1, which includes two high-temperature gas hole pipes 2 arranged on the resistance welding core rod 14 and parallel to the axial direction of the welded pipe 1, one end of the high-temperature gas hole pipe 2 is provided with an internal protective gas inlet 3, and the other end is closed, a plurality of internal protective gas outlets 4 are arranged outside the closed end of the high-temperature gas hole pipe 2, and a first high-temperature sealing gas curtain 5 and a second high-temperature sealing gas curtain 6 are arranged on both sides of the internal protective gas outlet 4.

[0054] The first and second high-temperature-resistant sealing gas curtains 5 and 6 are circular flexible fiber sealing gas curtains, the thickness of the first and second high-temperature-resistant sealing gas curtains 5 and 6 ranges from 20 to 50 mm, the first and second high-temperature-resistant sealing gas curtains 5 and 6 have an inner square and outer circle structure, the first and second high-temperature-resistant sealing gas curtains 5 and 6 are respectively sleeved on the resistance welding mandrels 14 before and after the welding area, the first and second high-temperature-resistant sealing gas curtains 5 and 6 and the resistance welding mandrels 14 are respectively fixed or filled with heat-resistant glue or high-temperature-resistant cotton, the heat-resistant glue is polytetrafluoroethylene heat-resistant glue, the high-temperature-resistant cotton is polycrystalline molybdenum high-temperature-resistant cotton, the first high-temperature-resistant sealing gas curtain 5 is provided with an inner burr scraper 15 at the front end, the outer surface of the welded pipe 1 at the position of the second high-temperature-resistant sealing gas curtain 6 is provided with a high-temperature-resistant fiber paving blanket 13, the material of the high-temperature-resistant fiber paving blanket 13 is zirconium-containing ceramic silicon aluminum, the high-temperature-resistant fiber paving blanket 13 is trapezoidal, the high-temperature-resistant gas hole pipe 2 can resist a temperature of 1600℃ or above, the inner protective gas outlet 4 has a hole diameter ranging from 2 to 5 mm, a hole spacing ranging from 2 to 4 mm, and a total length ranging from 20 to 40 mm.

[0055] In the step S4, the pipe outer gas protection device is located above the top of the welded pipe 1 and has a "Y" type high-temperature-resistant non-magnetic box body, a plurality of outer protective gas inlets 10 are arranged on the upper part of the high-temperature-resistant non-magnetic box body, and a plurality of outer protective gas outlets 11 are arranged on the lower part of the high-temperature-resistant non-magnetic box body, and the outer protective gas outlets 11 are provided with heat-resistant sealing adhesive tape ear curtains 12 between the outer protective gas outlets 11 and the welded pipe 1.

[0056] The pipe outer gas protection device comprises a high-temperature-resistant non-magnetic left side block 7, a high-temperature-resistant non-magnetic middle block 8 and a high-temperature-resistant non-magnetic right side block 9 which are connected in sequence, the high-temperature-resistant non-magnetic middle block 8 is parallel to the welding seam direction of the welded pipe 1, the included angle between the high-temperature-resistant non-magnetic left side block 7 and the high-temperature-resistant non-magnetic right side block 9 is the same as the joint angle before the strip steel is welded, a plurality of outer protective gas inlets 10 are arranged on the upper part of the high-temperature-resistant non-magnetic left side block 7, the high-temperature-resistant non-magnetic middle block 8 and the high-temperature-resistant non-magnetic right side block 9, respectively, a plurality of outer protective gas outlets 11 are arranged on the lower part of the high-temperature-resistant non-magnetic left side block 7, the high-temperature-resistant non-magnetic middle block 8 and the high-temperature-resistant non-magnetic right side block 9, respectively, the outer protective gas outlets 11 have a hole diameter ranging from 2 to 3 mm, the "Y" type high-temperature-resistant non-magnetic box body is fixed on the outer welding seam of the welded pipe 1 by a support, the protective gas outlet 11 in the middle of the non-magnetic box body is aligned with the occlusion point of the welding seam, the bottom of the non-magnetic box body is 20-50 mm away from the welding seam of the welded pipe, the material of the high-temperature-resistant gas hole pipe 2 is 99 corundum, and the material of the "Y" type high-temperature-resistant non-magnetic box body is 6061 aluminum alloy.

[0057] The step S4 includes the following steps:

[0058] S41: placing the inner gas protection device in the welding area of the welded pipe 1 and placing the outer gas protection device above the welding area of the welded pipe 1;

[0059] S42: when producing the high-frequency welded pipe with high alloy, the inner protection gas inlet 3 is connected to nitrogen or argon, and the outer protection "Y" type high-temperature non-magnetic box is connected to appropriate argon through the outer protection gas inlet 10, so that the inner and outer protection simultaneously play a gas protection role, and the high-frequency welding of the large-diameter Cr alloy plate can be completed in an environment isolated from air and water.

[0060] After the inner and outer gas protection devices are installed, the outer protection is connected to high-purity argon with a volume fraction of 99.9%, and the inner protection is connected to high-purity nitrogen with a volume fraction of 99.9%. Since the resistivity of the Cr alloy plate is higher than that of the carbon steel plate, the linear expansion coefficient is large, and the thermal conductivity is low, the inductive welding frequency of the large-diameter Cr alloy plate is 350±20 KHZ, and the welding speed is 18±3 m / min. The frequency control can obtain appropriate strength and toughness.

[0061] In the step S5, the normalizing heat treatment, Cr has a significant solute drag effect on the grain boundary, increases the stability of the supercooled austenite, and the phase transition point is reduced. The normalizing heat treatment is performed on the weld of the 1.0-10.0% Cr alloy high-frequency welded pipe by induction heating, and the temperature is 910±20℃. After normalizing, the weld structure is more fine, without cracks and inclusions, and a complex structure mainly composed of pearlite P, quasi-polygonal ferrite QF and polygonal ferrite PF is obtained, which can refine the weld structure and eliminate stress concentration, greatly prevent corrosion under CO2 / H2S corrosion conditions, and reduce the groove corrosion sensitivity coefficient of the weld.

[0062] In the step S6, the aging heat treatment, the whole pipe body is subjected to aging heat treatment by induction heating, and the whole pipe body is heated to 500-550℃ and aged for 20-60 min, so as to reduce the yield strength of the pipe body under the condition that the weld toughness is unchanged, and adjust the yield strength ratio of the pipe.

[0063] In the step S8, the straightening process, in order to ensure that the outer size of the steel pipe after forming and heat treatment meets the standard requirements, the welded pipe is subjected to sizing and straightening, so that the welded pipe has good outer size precision and straightness;

[0064] Example 2

[0065] According to the large-diameter Cr alloy high-frequency welded pipe and the processing method described in Example 1, a Φ406.4×11mm Cr alloy high-frequency welded pipe of L485 steel grade is processed, and the specific process is as follows:

[0066] (1) Raw material: L485 steel grade medium-high alloy coil plate with wall thickness of 11 mm was used, and its chemical composition was shown in Table 1 (wt%).

[0067] Table 1 Chemical composition analysis of L485 medium alloy coil plate (wt%)

[0068]

[0069] (2) Welded pipe manufacturing: L485 steel grade medium Cr alloy plate coil was used to produce high frequency welded steel pipe with outer diameter of Φ406.4 mm and wall thickness of 11 mm. After uncoiling, flattening and edge milling, the strip steel width was accurately controlled at 1285 mm, and the plate edge waveform was controlled by using a row of rollers. When high frequency induction resistance welding was used, Cr-Mo hollow vertical rollers and hollow side extrusion rollers were selected, and internal and external gas protection devices were installed respectively. In the external protection volume fraction of 99.9% high purity argon and internal protection volume fraction of 99.9% high purity nitrogen gas protection environment, the welding current, voltage process parameters were adjusted, the small opening angle was controlled, the large extrusion amount of the weld was adjusted and controlled to 6.3 mm, the sizing amount was 5.8 mm, the weld metal flow rising angle was 69°-72°, the welding frequency was 345 KHZ, the welding speed was 17 m / min, and the high frequency welded pipe with outer diameter of 406.4 mm and wall thickness of 11 mm was welded. Then, the weld of the welded pipe was on-line normalized at 910℃, and the water cooling start temperature was controlled at 380℃. After welding, the welded pipe was cut into pipe sections with a length of about 12 m. The full pipe body of the high frequency welded pipe was treated by induction heating for aging heat treatment, heated at 525℃, and air cooled after aging treatment for 30 min. Under the condition of ensuring the weld toughness, the pipe yield ratio was adjusted. Then, after the sizing flying shear, straightening, X-ray inspection and ultrasonic inspection, pipe end beveling, appearance size inspection and other processes were qualified, the physical and chemical performance detection was carried out.

[0070] (3) Mechanical property test: the pipe ring of L485 steel grade medium Cr alloy high frequency welded pipe was cut to measure the circumferential opening amount of-10 mm. The pipe body yield strength Rt 0.5 : 485-585 MPa, pipe body tensile strength R b : 540-680 MPa, pipe body yield ratio: 0.75-0.88, pipe body elongation: 28-34%, weld tensile strength Rm≥485 MPa, -10℃ pipe parent AkV: 180-210 J, -10℃ weld AkV: 110-188 J. When the weld is at 0° and 90° position, the flattening test is carried out, and when the two sides of the welded pipe are pressed to fit, all the welds are free of any cracks and cracking phenomenon. According to API 5L standard, the mechanical property test meets the standard requirements.

[0071] (4) Weld comparison test without adding gas protection device and with adding gas protection device

[0072] The L485 steel grade Cr alloy high frequency welded pipe is produced, and the welding without inner and outer gas protection device and the welding with gas protection device are compared, and other pipe manufacturing process parameters are unchanged. The nondestructive ultrasonic detector is used for weld detection, the weld without inner and outer gas protection device is detected to have cracks in the weld, the impact energy at-10 DEG C is 10-28J, the weld with inner and outer gas protection device has no cracks, and the impact energy at-10 DEG C is 110-188J.

[0073] Figure 2 The macroscopic morphology of the weld without inner and outer gas protection device is shown, and a large crack perpendicular to the thickness appears in the center of the weld, when the welding is not protected by gas, the high melting point oxide of Cr cannot be squeezed out of the weld zone, and a large number of cracks caused by unmelted and inclusions are generated in the center of the weld. Figure 3 The macroscopic morphology of the weld with inner and outer gas protection device is shown, and the weld has no cracks and inclusions, and a complex phase structure mainly composed of pearlite P, quasi-polygonal ferrite PF and polygonal ferrite QF is obtained, the weld has no defects, and the welding quality is high.

[0074] Figure 4 The L485 steel grade Φ406.4*11mm Cr alloy high frequency welded pipe is manufactured on the high frequency welded pipe unit by using the inner and outer gas protection device, the high magnification microstructure of the weld of the L485 steel grade Φ406.4*11mm Cr alloy high frequency welded pipe is shown, the center of the weld is enlarged by 400 times, and it can be seen that the center of the weld has no defects, and the structure is small and uniform, which indicates that the Cr alloy high frequency welded pipe is successfully welded.

[0075] Corrosion comparison test: the L485 steel grade Cr alloy high frequency welded pipe is subjected to CO2 corrosion comparison test, the conventional L485 carbon steel high frequency welded pipe is selected as the comparison test sample, in a high temperature and high pressure kettle, a certain site CO2 and bacteria, SRB content is 10000 / ml, after soaking for 15 days, the corrosion performance test results are shown in Table 2, the corrosion pitting depth of the pipe body and the welded joint of the Cr alloy high frequency welded pipe is ≤10μm, and the average corrosion rate is far lower than that of the comparison carbon steel sample of the same steel grade, and it can be seen that the Cr alloy high frequency welded pipe has excellent mechanical and corrosion resistance comprehensive performance.

[0076] Table 2 Corrosion performance test results

[0077]

[0078] From the embodiment, it can be seen that the main performance detection result of the large-diameter medium Cr alloy high-frequency welded pipe and the manufacturing method is as follows: the medium Cr alloy high-frequency welded pipe manufactured by the embodiment has no defect in the weld, the mechanical property of the weld is excellent, and the high-frequency straight seam welding production capacity of the large-diameter medium Cr and other alloy element high-frequency welded pipe material is high.

[0079] The above merely provides the preferred embodiment of the present application, and the protection scope of the present application is not limited to this. Any change or replacement within the technical range disclosed by the present application can be easily thought by those skilled in the art, and should be covered within the protection scope of the present application.

Claims

1. A large diameter, high frequency welded pipe of a high Cr alloy, characterized by: The chemical composition of the large-diameter medium Cr alloy high-frequency welded pipe is C: ≤0.10%, Si: ≤0.50%, Mn: ≤2.0%, P: ≤0.020%, S: ≤0.005%, Cr: 1.0-10.0%, Ni: ≤5.0%, Cu: ≤2.0%, Mo: ≤2.0%, Nb+V+Ti: ≤0.15%, and the rest is iron and inevitable impurities, and the processing method of the large-diameter medium Cr alloy high-frequency welded pipe comprises the following steps: S1: butt welding: butt joint of the head and tail of the medium Cr alloy coil plate; S2: planing: planing the width of the medium Cr alloy coil plate by ±0.20mm; S3: forming: adjusting the extrusion amount of the medium Cr alloy coil plate to 6±0.5mm and the sizing amount to 6.0±0.5mm in the roll forming process; when welded and formed, the hollow vertical roll and the hollow side extrusion roll made of high-temperature Cr-Mo material are used, and cooling circulating water is injected into the hollow vertical roll and the hollow side extrusion roll for cooling; S4: internal and external gas protection high-frequency welding: when high-frequency induction resistance welding is used, the internal and external gas protection devices are used, the external gas protection device is connected with 99.9% high-purity argon, and the internal gas protection device is connected with 99.9% high-purity nitrogen, the high-frequency induction welding frequency of the large-diameter medium Cr alloy plate is 350±20KHz, and the welding speed is 18±3m / min; S5: normalizing heat treatment: the temperature is 910±20℃; S6: aging heat treatment: heating the whole pipe body to 500-550℃ and aging for 20-60min; S7: sizing flying shear: cutting the high-frequency welded pipe according to the designed length; S8: straightening; S9: X-ray inspection and ultrasonic inspection; S10: pipe end beveling; S11: appearance size inspection; S12: physical and chemical and corrosion resistance performance test: chemical composition analysis, charpy impact, flattening, tensile and corrosion test are carried out on the large-diameter medium Cr alloy high-frequency welded pipe according to the test batch, and the large-diameter medium Cr alloy high-frequency welded pipe processing is completed.

2. The high frequency induction welded pipe according to claim 1, wherein: The yield strength of the large-diameter medium Cr alloy high-frequency welded pipe is ≥360MPa, the pipe diameter is 168-660mm, and the wall thickness is ≤25.4mm.

3. The high frequency induction welded pipe according to claim 1, wherein: In the step S4, the internal gas protection device is located in the welded pipe (1) and comprises two high-temperature gas hole pipes (2) parallel to the axial direction of the welded pipe (1) arranged on the resistance welding core rod (14), one end of the high-temperature gas hole pipe (2) is provided with an internal protection gas inlet (3), and the other end is closed, a plurality of internal protection gas outlets (4) are arranged on the outer side of the closed end of the high-temperature gas hole pipe (2), and the two sides of the internal protection gas outlet (4) are respectively provided with a first high-temperature sealing gas curtain (5) and a second high-temperature sealing gas curtain (6).

4. The high frequency induction welded pipe according to claim 3, wherein: The first and second high-temperature-resistant sealing air curtains (5, 6) are circular flexible fiber sealing air curtains, the thickness of the first and second high-temperature-resistant sealing air curtains (5, 6) ranges from 20 to 50 mm, the first and second high-temperature-resistant sealing air curtains (5, 6) have an inner square and outer circle structure, the first and second high-temperature-resistant sealing air curtains (5, 6) are respectively sleeved on the resistance welding mandrels (14) before and after the welding area, the first and second high-temperature-resistant sealing air curtains (5, 6) and the resistance welding mandrels (14) are respectively fixed or filled with heat-resistant glue or high-temperature-resistant cotton, the heat-resistant glue is polytetrafluoroethylene heat-resistant glue, the high-temperature-resistant cotton is polycrystalline molybdenum high-temperature-resistant cotton, the first high-temperature-resistant sealing air curtain (5) is provided with an inner burr scraper (15) at the front end, the outer surface of the welded pipe (1) at the position of the second high-temperature-resistant sealing air curtain (6) is provided with a high-temperature-resistant fiber paving blanket (13), the high-temperature-resistant fiber paving blanket (13) is trapezoidal, the material of the high-temperature-resistant fiber paving blanket (13) is zirconium-containing ceramic aluminum silicate, the high-temperature-resistant air hole pipe (2) can resist a temperature of 1600 DEG C or above, the inner protective gas outlet (4) has a hole diameter ranging from 2 to 5 mm, a hole spacing ranging from 2 to 4 mm, and a total length ranging from 20 to 40 mm.

5. The high frequency induction welded pipe according to claim 4, wherein: In the step S4, the outer gas protection device is located above the top of the welded pipe (1) outside, which is a "Y" type high-temperature-resistant non-magnetic box body, the upper part of the high-temperature-resistant non-magnetic box body is provided with a plurality of outer protective gas inlets (10), and the lower part is provided with a plurality of outer protective gas outlets (11), the outer protective gas outlet (11) and the welded pipe (1) are provided with a heat-resistant sealing adhesive tape curtain (12).

6. The high frequency induction welded pipe according to claim 5, wherein: The pipe outer gas protection device comprises a high-temperature-resistant non-magnetic left side block (7), a high-temperature-resistant non-magnetic intermediate block (8) and a high-temperature-resistant non-magnetic right side block (9) connected in sequence, the high-temperature-resistant non-magnetic intermediate block (8) is parallel to the welding seam direction of the welded pipe (1), the included angle of the high-temperature-resistant non-magnetic left side block (7) and the high-temperature-resistant non-magnetic right side block (9) is the same as the joint angle before the strip steel is welded, a plurality of outer protection gas inlets (10) are arranged on the high-temperature-resistant non-magnetic left side block (7), the high-temperature-resistant non-magnetic intermediate block (8) and the high-temperature-resistant non-magnetic right side block (9), a plurality of outer protection gas outlets (11) are arranged on the high-temperature-resistant non-magnetic left side block (7), the high-temperature-resistant non-magnetic intermediate block (8) and the high-temperature-resistant non-magnetic right side block (9), the outer protection gas outlet (11) has a hole diameter range of 2-3 mm, the "Y" type high-temperature-resistant non-magnetic box body is fixed on the outer welding seam of the welded pipe (1) by a support, the protection gas outlet (11) in the middle of the non-magnetic box body is aligned with the bite point of the welding seam, the bottom of the non-magnetic box body is 20-50 mm away from the outer welding seam of the welded pipe, the material of the high-temperature-resistant gas hole pipe (2) is 99 corundum, and the material of the "Y" type high-temperature-resistant non-magnetic box body is 6061 aluminum alloy.

7. The high frequency induction welded pipe according to claim 6, wherein: In the step S4, the inner and outer gas protection high-frequency welding specifically comprises the following steps: S41: placing the inner pipe gas protection device in the inner welding area of the welded pipe (1) and placing the outer pipe gas protection device above the outer welding area of the welded pipe (1); S42: when producing the Cr alloy high-frequency welded pipe, the inner protection gas inlet (3) is connected with nitrogen, the outer protection "Y" type high-temperature-resistant non-magnetic box body is connected with appropriate argon through the outer protection gas inlet (10), the inner and outer protection simultaneously plays a gas protection role, and the large-diameter Cr alloy plate high-frequency welding can be completed in an environment isolated from air and water.

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