S420 high-strength steel welding construction method for jacket at water depth of 300 meters

Abstract

The invention discloses a 300-meter water depth jacket S420 high-strength steel welding construction method which is characterized in that preheating treatment is carried out in the processes of plate cutting and blanking, plate pre-bending, reel pipe closing, transition groove cutting and longitudinal seam welding, and during pre-bending, a multi-time slow pressing and pre-bending mode is adopted, so that mechanical indentations can be prevented from occurring in the pre-bending process; during pipe rolling, pipe rolling and opening closing are completed in a multi-rolling slow forming mode, and rolling'dead bending 'can be avoided; in the process of cutting and grinding the transition groove, the workpiece is synchronously heated, so that defects can be avoided in the grinding process, and the influence on subsequent welding is avoided; in the longitudinal seam welding process, the requirement for the preheating temperature is improved, only electric heating can be adopted during preheating, the welding process is strictly controlled, and after-heating hydrogen elimination treatment is conducted after welding, so that the hydrogen content is reduced, and cracks are avoided; the construction quality of the second sea foundation is better guaranteed, the potential safety hazard of offshore operation of the jacket is reduced, and it is guaranteed that the main structure meets the service requirement.

Description

Technical Field

[0001] The present invention relates to the field of welding technology, and in particular to a 300-meter-deep water conductor jacket S420 high-strength steel welding construction method. Background Art

[0002] As offshore oil and gas development gradually moves towards deep water, in order to ensure the overall strength and functional requirements of the platform, the thickness and quality of the steel plates used in the offshore engineering jacket structure are constantly increasing, which leads to increasing construction difficulty and development costs. The Liuhua 11-1 / 4-1 oilfield jacket under construction is located in the South China Sea. The water depth of the oilfield sea area is 300m to 400m. The fixed platform of this project has a launching depth of 330 meters, and the sea conditions in the sea area are harsh. The internal wave currents and complex sites in the sea area have put forward very high requirements on the adaptability of the jacket design.

[0003] At present, most of the domestic jacket platforms use DH36 and EH36 steel grades, which are high-strength steels with a minimum yield strength of 355Mpa. If the material selection and design is carried out according to conventional standard parameters, the weight of Liuhua 11-1 jacket, namely "Haiji No. 2", will reach more than 45,000 tons, which will exceed the installation and transportation capacity of the current marine resources, and the current construction unit site capacity cannot meet the construction requirements of jackets of this size and weight. Therefore, the Liuhua project uses S420 domestic ultra-high-strength steel to replace ordinary DH36 high-strength steel to reduce the weight of the "Haiji No. 2" jacket.

[0004] Since the jacket is immersed in seawater all year round, it needs to withstand various severe sea conditions. Steel The technical indicators are high, not only need to have high strength to resist the above water surface Wind flow impact also requires good welding and processing performance to ensure the safety of the overall structure of the jacket. The S420 high-strength steel used in the "Haiji No. 2" jacket has a higher yield strength than the conventional high-strength steel DH36 used in the "Haiji No. 1" jacket, but its own carbon content and crack sensitivity index are higher, so it has higher crack sensitivity and lower weldability. The conventional high-strength steel DH36 material used in the "Haiji No. 1" jacket is delivered in the normalized state, while the S420 high-strength steel used in the "Haiji No. 2" jacket is in the modulated state AP I Spec.2YGr.60. The metallographic structure after quenching and tempering is tempered troostite, so it is more sensitive to thermal processing and has a greater tendency to crack. At the same time, the maximum wall thickness of S420 used in Liuhua catheter rack is 100mm. Due to the complex alloy system of S420 ultra-high strength steel, the thick plate is affected by the rolling manufacturing process pressure and the thermodynamics of steel plate thermal expansion and contraction. The density of the central structure of the steel plate is significantly lower than that of the surface, and the hardening tendency is greater, which is easy to form cold cracks during welding. Therefore, it is necessary to strictly control the welding construction method of S420 high-strength steel to avoid cracks or other defects. Summary of the invention

[0005] In order to overcome the shortcomings of the prior art, the purpose of the present invention is to provide a 300-meter water depth jacket S420 high-strength steel welding construction method, which can avoid cracks or other defects that may occur in the S420 high-strength steel during processing and welding, better ensure the construction quality of "Haiji No. 2", reduce the safety hazards of jacket offshore operations, and ensure that the main structure meets service requirements.

[0006] To solve the above problems, the technical solution adopted by the present invention is as follows: A 300-meter water depth jacket S420 high-strength steel welding construction method comprises the following steps:

[0007] Step S100, cutting: determine the size and shape of the material to be cut, cut the required plate from the S420 high-strength steel plate, and reserve a plate margin when cutting;

[0008] Step S200, pre-bending the sheet: before formal rolling, the sheet is pre-bent. When the sheet is pre-bent, multiple slow-pressing pre-bending methods are adopted. The feed amount each time is controlled between 2mm and 3mm, and multiple slow-pressing steps are performed at the leading position of each pre-bending. After the pre-bending is completed, secondary cutting is performed;

[0009] Step S300, tube rolling and closing: after the plate is pre-bent, a plate rolling machine is used to roll the plate. During the tube rolling process, the downward pressure of the roller on the plate rolling machine is controlled to be between 2 mm and 4 mm, and the tube rolling and closing is completed in a multi-roll slow forming manner;

[0010] Step S400, transition groove cutting: cutting the transition groove at the joint part, and grinding the transition groove. During the cutting and grinding process, heating needs to be performed simultaneously;

[0011] Step S500, longitudinal seam welding: before welding, the welding part and the edge surface of the weld are cleaned and preheated before welding. The preheating before welding is performed by electric heating. When the thickness T of the base material is 13<T≤38mm, the preheating temperature is at least 65℃, when 38<T≤65mm, the preheating temperature is at least 110℃, when T>65mm, the preheating temperature is at least 150℃. After preheating, welding is performed and post-heat dehydrogenation treatment is performed;

[0012] Step S600, roundness calibration after welding;

[0013] Step S700, inspection processing: grinding and cleaning the weld after welding, inspection and non-destructive testing;

[0014] Among them, in steps S100 to S600, the workpiece needs to be preheated.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: the welding construction method is to preheat the plate before cutting and blanking, which can prevent the plate from cutting cracks; after the plate is blanked, the plate is first preheated and then pre-bent. During pre-bending, multiple slow-pressure pre-bending methods are used to avoid mechanical indentations during the pre-bending process; after the plate is pre-bent, the tube is rolled and closed, and preheating treatment is performed before the tube is rolled, which can improve the forming performance of the steel plate and reduce the processing difficulty. When rolling the tube, the tube is rolled and closed by a multi-roll slow-forming method, which can avoid the formation of a rolled "dead bend"; after rolling the tube, the transition groove is cut, and the transition groove is polished after cutting. In the process of cutting and polishing, the workpiece is heated simultaneously, which can avoid defects during polishing and avoid affecting subsequent welding; in the longitudinal seam welding process, the requirements for the preheating temperature are improved, and only electric heating can be used during preheating, the welding process is strictly controlled, and post-heat dehydrogenation treatment is performed after welding to reduce the hydrogen content and avoid cracks; finally, post-weld roundness calibration and inspection processing are performed. The welding construction method of the present invention requires preheating of the workpiece in steps S100 to S600, and realizes rolling by means of multiple slow-pressure pre-bending and multiple-roll slow-forming. It performs synchronous heating when cutting and grinding the transition groove, and strictly controls the welding process, so as to avoid cracks or other defects that may occur in the S420 high-strength steel during the welding process, better ensure the construction quality of "Haiji No. 2", reduce the safety hazards of offshore operations of the jacket, and ensure that the main structure meets the service requirements.

[0016] In the above-mentioned 300-meter-deep water jacket S420 high-strength steel welding construction method, in step S500, the workpiece is preheated before welding begins and before any welding interruption is resumed.

[0017] In the above-mentioned 300-meter-deep water jacket S420 high-strength steel welding construction method, in step S500, welding is not stopped until at least the bottom welding is completed and six welds are welded continuously, or before the thickness of the deposited metal reaches 1 / 3 of the weld thickness.

[0018] In the above-mentioned 300-meter-deep water jacket S420 high-strength steel welding construction method, in step S500, during preheating before welding, if the base material thickness T exceeds 25 mm and the preheating and welding are on the same side, the preheating source is removed for at least one minute before measuring the preheating temperature.

[0019] In the above-mentioned 300-meter-deep water jacket S420 high-strength steel welding construction method, in step S500, during preheating before welding, if the thickness T of the base material exceeds 25 mm and the welding is double-sided welding, preheating is performed simultaneously on both sides of the workpiece.

[0020] In the above-mentioned 300-meter-deep water jacket S420 high-strength steel welding construction method, in step S500, during preheating before welding, the preheating range in all directions of the weld is not less than 75 mm and not less than the maximum thickness of the workpiece.

[0021] In the above-mentioned 300-meter-deep water jacket S420 high-strength steel welding construction method, in step S500, when the base material temperature is lower than 0°C, the preheating temperature is at least 50°C, and the working environment temperature is greater than -20°C when welding starts.

[0022] In the above-mentioned 300-meter-deep water jacket S420 high-strength steel welding construction method, in step S100, a cutting zone is drawn on the S420 high-strength steel plate, and the entire steel plate is preheated. After preheating to the minimum required temperature, the entire steel plate is continuously heated, and a flame gun is used to heat along the cutting zone, and then cutting is performed along the cutting zone. After cutting is completed, the cutting zone is covered with insulation cotton, and the entire steel plate is continuously heated for a period of time before the heating is stopped.

[0023] In the above-mentioned 300-meter-deep water jacket S420 high-strength steel welding construction method, in step S500, after welding is completed, post-heat dehydrogenation treatment is performed before the temperature in the weld preheating area is lower than 130°C, the post-heating temperature is maintained between 180°C and 210°C, the post-heating time is at least 2h, and when the parent material thickness T exceeds 50mm, the post-heating time increases by 1h for every 25mm increase in thickness. After the post-heat dehydrogenation is completed, insulation cotton is used for wrapping and insulation for 2h to 4h.

[0024] In the above-mentioned 300-meter-deep water jacket S420 high-strength steel welding construction method, after step S700, the qualified pipe section is extended. During the extension, the annular seam is preheated and welded. When welding inside the pipe, after welding for a period of time, the operation is stopped and the weld is allowed to cool for a period of time before continuing welding.

[0025] The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a step diagram of the construction method of an embodiment of the present invention. DETAILED DESCRIPTION

[0027] The embodiments of the present invention are described in detail below. Figure 1 The embodiment of the present invention provides a 300-meter-deep water jacket S420 high-strength steel welding construction method, comprising the following steps:

[0028] Step S100, cutting: determine the size and shape of the material to be cut, cut the required plate from the S420 high-strength steel plate, and reserve a plate margin when cutting;

[0029] Step S200, pre-bending the sheet: before formal rolling, the sheet is pre-bent. When the sheet is pre-bent, multiple slow-pressing pre-bending methods are adopted. The feed amount each time is controlled between 2mm and 3mm, and multiple slow-pressing steps are performed at the leading position of each pre-bending. After the pre-bending is completed, secondary cutting is performed;

[0030] Step S300, tube rolling and closing: after the plate is pre-bent, a plate rolling machine is used to roll the plate. During the tube rolling process, the downward pressure of the roller on the plate rolling machine is controlled to be between 2 mm and 4 mm, and the tube rolling and closing is completed in a multi-roll slow forming manner;

[0031] Step S400, transition groove cutting: cutting the transition groove at the joint part, and grinding the transition groove. During the cutting and grinding process, heating needs to be performed simultaneously;

[0032] Step S500, longitudinal seam welding: before welding, the welding part and the edge surface of the weld shall be cleaned, the area within 25 mm from the groove shall be fully polished, and preheating shall be performed before welding. The preheating before welding is performed by electric heating. When the thickness T of the parent material is 13<T≤38mm, the preheating temperature is at least 65℃, when 38<T≤65mm, the preheating temperature is at least 110℃, and when T>65mm, the preheating temperature is at least 150℃. After preheating, welding is performed and post-heat dehydrogenation treatment is performed;

[0033] Step S600, roundness calibration after welding;

[0034] Step S700, inspection processing: grinding and cleaning the weld after welding, inspection and non-destructive testing;

[0035] Among them, in steps S100 to S600, the workpiece needs to be preheated.

[0036] The welding construction method is to cut and unload the plate after preheating, which can prevent the plate from cutting cracks; after unloading the plate, the plate is first preheated and then pre-bent. During pre-bending, multiple slow-pressure pre-bending methods are used to avoid mechanical indentations during the pre-bending process; the plate is rolled and closed after pre-bending, and preheating treatment is performed before rolling the tube, which can improve the forming performance of the steel plate and reduce the processing difficulty. When rolling the tube, the tube is rolled and closed by a multi-roll slow-forming method, which can avoid the formation of a rolling "dead bend"; after rolling the tube, the transition groove is cut, and the transition groove is polished after cutting. In the process of cutting and polishing, the workpiece is heated simultaneously, which can avoid defects during polishing and avoid affecting subsequent welding; in the longitudinal seam welding process, the requirements for preheating temperature are increased, and only electric heating can be used during preheating, the welding process is strictly controlled, and post-heat dehydrogenation treatment is performed after welding to reduce the hydrogen content and avoid cracks; finally, post-weld roundness calibration is performed and inspection is reported. The welding construction method of the present invention requires preheating of the workpiece in steps S100 to S600, and realizes rolling by means of multiple slow-pressure pre-bending and multiple-roll slow-forming. It performs synchronous heating when cutting and grinding the transition groove, and strictly controls the welding process, so as to avoid cracks or other defects that may occur in the S420 high-strength steel during the welding process, better ensure the construction quality of "Haiji No. 2", reduce the safety hazards of offshore operations of the jacket, and ensure that the main structure meets the service requirements.

[0037] For DH36 steel, when the pipe section is formed, preheating is only required during formal welding. In this welding construction method, preheating treatment is required in steps S100 to S600 to avoid cracks, ensure low hydrogen content of the weld, and control welding deformation and stress. In the welding process of step S500, the welding material model used is DW-A55LSR, and flux-cored gas shielded welding is used for welding. The shielding gas is a mixed gas composed of 80% argon + 20% carbon dioxide, and the wind speed or air flow speed in the welding area is kept below 8km / h. Due to the poor weldability of S420 high-strength steel, DW-A55LSR welding wire is required for welding throughout the construction cycle. During welding, the welding process needs to be strictly controlled. Before formal welding, the welder needs to be trained in theory and practice for more than two weeks to familiarize the welder with the welding process to the greatest extent, ensure welding quality, and avoid cracks. After the welder passes the theoretical and practical assessments, the welding of the first five welds is tracked, and NDT inspection is carried out in time after each weld. The second weld is carried out after the inspection result is qualified, until the five welds are completed. If there is a repair during the period, the welding work of S420 high-strength steel shall not be participated in. During the construction of the project, the S420 parent material and welding materials used in the construction need to be re-inspected, and samples of each batch of welding materials shall be retained for reference. In order to better ensure the construction quality of "Haiji No. 2", reduce the safety hazards of offshore operations of the jacket, and ensure that the main structure meets the service requirements, this welding construction method adds the re-inspection of TKY key nodes.

[0038] Furthermore, in order to strictly control the welding quality, in step S500, the workpiece needs to be preheated before welding starts and before any welding is interrupted and restarted. When the thickness of the base material T>50mm, the maximum interlayer temperature is 200℃, when T≤50mm, the maximum interlayer temperature is 220℃, when the base material temperature is lower than 0℃, the preheating temperature is at least 50℃, and the ambient temperature for starting welding is greater than -20℃, that is, when the ambient temperature is lower than -20℃, welding work should not be carried out in theory. If welding work must be carried out, it should be carried out under special insulation measures. Before welding, a wind, rain and snow shelter should be set up to meet the welding requirements in windy, rainy and snowy weather. During the welding process, since the gap between the interlayer temperature and the preheating temperature decreases, it is necessary to ensure that the temperature during the welding process does not exceed the interlayer temperature. After welding for a certain period of time, it is necessary to stop halfway and wait for a period of time before continuing the welding work.

[0039] Further, in step S500, before at least the backing welding is completed and six welds are welded continuously, or before the thickness of the deposited metal reaches 1 / 3 of the weld thickness, welding is not stopped. After welding is stopped and before continuing welding, the weld is first checked for cracks. Welding is continued after the inspection is qualified, and preheating is continued. In step S500, during preheating before welding, the preheating range in all directions of the weld is not less than 75mm and not less than the maximum thickness of the workpiece. During the preheating process, it is necessary to prevent the heated surface from overheating, melting or bluing to cause material failure. Tools such as temperature measuring crayons, contact pyrometers, and temperature displays can be used to measure the preheating temperature and interlayer temperature, but these tools cannot be used in the weld area. During preheating before welding, if the thickness T of the parent material exceeds 25mm and the preheating and welding are on the same side, the preheating source is removed for at least one minute before measuring the preheating temperature. If the thickness T of the parent material exceeds 25mm and the welding is double-sided welding, preheating is performed simultaneously on both sides of the workpiece.

[0040] When preheating before welding, the thermocouple should be fixed at least 25mm away from the edge of the weld by capacitor discharge welding. The welding layer should be cleaned without residue splashing, etc. When the back is cleaned, the root should be cleaned by carbon arc air gouging or grinding. The minimum depth of the root is 6mm, and before the back welding, it must be ensured that the root is cleared to the intact weld metal and the carburized layer is completely removed by grinding. For high-strength steels such as DH36, it is not recommended to perform post-heat treatment after welding. However, for S420 high-strength steel, after welding, the temperature in the weld preheating area is lower than 130℃ before post-heat dehydrogenation treatment is performed. The post-heating temperature is maintained between 180℃ and 210℃, and the minimum post-heating time is 2h. When the thickness T of the parent material exceeds 50mm, the post-heating time increases by 1h for every 25mm increase in thickness. After the post-heat dehydrogenation is completed, it is wrapped with thermal insulation cotton for insulation. The insulation time is 2h to 4h to reduce the cooling rate. Post-heat dehydrogenation treatment can reduce the hydrogen content and avoid cracks.

[0041] Since S420 high-strength steel has higher strength and is more difficult to grind, and the longest grinding length of the transition groove in the "Haiji No. 2" conductor rack project is 180mm, defects are more likely to occur when cutting and grinding the transition groove. In order to avoid defects during the cutting and grinding process, it is necessary to cut and grind under heating. It is best to cooperate with two people, one responsible for preheating and the other responsible for cutting and grinding. S420 high-strength steel has higher strength, so it is more difficult to cut and is more likely to produce cutting cracks, which in turn affects the subsequent formal welding. Therefore, in step S100, a cutting band is drawn on the S420 high-strength steel plate, and the entire steel plate is preheated. After preheating to the minimum required temperature, the entire steel plate is continuously heated to ensure that the entire steel plate is heated evenly, and a flame gun is used to heat along the cutting band. After the flame gun runs empty along the cutting band for multiple times to heat, it is cut along the cutting band. The speed during cutting is slowed down to reduce the probability of cutting cracks. After the cutting is completed, the cutting belt is covered with heat preservation cotton, and the entire steel plate is heated continuously for a period of time, and then the heating is stopped. The cutting belt is tempered at a low temperature to further reduce the probability of cutting cracks.

[0042] After obtaining the pipe section through steps S100 to S700, the qualified pipe section is extended. When extending, the annular seam is preheated and welded. When welding in the pipe, after welding for a period of time, the operation is stopped and the weld is allowed to cool for a period of time before continuing welding. Since the preheating temperature is high, the welding time is long, and the gap between the interlayer temperature of welding and the preheating temperature is reduced, therefore, after welding for a period of time, stop and wait for a period of time, which not only allows the operator to rest, but also can better control the interlayer temperature. During welding, the minimum length of spot welding is 50mm, and the thickness of the spot welding layer and the distribution of the spot welding position must ensure the strength requirements of the welding joint teaming and fixing to avoid welding cracks. When spot welding requires deposition on the final weld, the edge of the spot welding should be polished clean, and the smooth transition is better melted into the weld. When spot welding is not required to be deposited on the final weld, all spot welds should be polished away and at least 25mm on both sides of the welding area should be cleaned by grinding or other means to ensure that the weld is smooth, without undercuts, lack of fusion, incomplete filling and other defects, and then an appearance inspection can be carried out.

[0043] It should be noted that in the description of the present invention, if there are any orientation descriptions, such as up, down, front, back, left, right, etc., the orientations or positional relationships indicated are all based on the orientations or positional relationships shown in the drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed or operated in a specific orientation, and cannot be understood as a limitation on the present invention.

[0044] In the description of the present invention, "several" means one or more, "more" means two or more, "greater than", "less than", "exceed" etc. are understood to exclude the number itself, and "above", "below", "within" etc. are understood to include the number itself. If there is a description of "first" or "second", it is only used to distinguish the technical features, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features or implicitly indicating the order of the indicated technical features.

[0045] In the description of the present invention, unless otherwise clearly defined, terms such as setting, installing, connecting, etc. should be understood in a broad sense, and technicians in the relevant technical field can reasonably determine the specific meanings of the above terms in the present invention based on the specific content of the technical solution.

[0046] The above-mentioned embodiments are only preferred embodiments of the present invention and cannot be used to limit the scope of protection of the present invention. Any non-substantial changes and substitutions made by technicians in this field on the basis of the present invention shall fall within the scope of protection required by the present invention.

Claims

1. A 300-meter-deep water jacket S420 high-strength steel welding construction method, characterized in that: The steps include: Step S100, cutting: determine the size and shape of the material to be cut, cut the required plate from the S420 high-strength steel plate, and reserve a plate margin when cutting; Step S200, pre-bending the sheet: before formal rolling, the sheet is pre-bent. When the sheet is pre-bent, multiple slow-pressing pre-bending methods are adopted. The feed amount each time is controlled between 2mm and 3mm, and multiple slow-pressing steps are performed at the leading position of each pre-bending. After the pre-bending is completed, secondary cutting is performed; Step S300, tube rolling and closing: after the plate is pre-bent, a plate rolling machine is used to roll the plate. During the tube rolling process, the downward pressure of the roller on the plate rolling machine is controlled to be between 2 mm and 4 mm, and the tube rolling and closing is completed in a multi-roll slow forming manner; Step S400, transition groove cutting: cutting the transition groove at the joint part, and grinding the transition groove. During the cutting and grinding process, heating needs to be performed simultaneously; Step S500, longitudinal seam welding: before welding, the welding part and the edge surface of the weld are cleaned and preheated before welding. The preheating before welding is performed by electric heating. When the thickness T of the base material is 13<T≤38mm, the preheating temperature is at least 65℃, when 38<T≤65mm, the preheating temperature is at least 110℃, when T>65mm, the preheating temperature is at least 150℃. After preheating, welding is performed and post-heat dehydrogenation treatment is performed; Step S600, roundness calibration after welding; Step S700, inspection processing: grinding and cleaning the weld after welding, inspection and non-destructive testing; Among them, in steps S100 to S600, the workpiece needs to be preheated.

2. The 300-meter-deep water jacket S420 high-strength steel welding construction method according to claim 1 is characterized in that: In step S500, the workpiece is preheated before welding begins and before any welding interruption is resumed.

3. The 300-meter-deep water jacket S420 high-strength steel welding construction method according to claim 1 is characterized in that: In step S500, welding is not stopped until at least the backing welding is completed and six weld passes are welded continuously, or until the thickness of the deposited metal reaches 1 / 3 of the weld thickness.

4. The 300-meter-deep water jacket S420 high-strength steel welding construction method according to claim 1 is characterized in that: In step S500, during preheating before welding, if the base material thickness T exceeds 25 mm and preheating and welding are performed on the same side, the preheating source is removed for at least one minute before measuring the preheating temperature.

5. The 300-meter-deep water jacket S420 high-strength steel welding construction method according to claim 1 is characterized in that: In step S500, during preheating before welding, if the base material thickness T exceeds 25 mm and the welding is double-sided welding, preheating is performed simultaneously on both sides of the workpiece.

6. The 300-meter-deep water jacket S420 high-strength steel welding construction method according to claim 1 is characterized in that: In step S500, during preheating before welding, the preheating range in all directions of the weld is not less than 75 mm and not less than the maximum thickness of the workpiece.

7. The 300-meter-deep water jacket S420 high-strength steel welding construction method according to claim 1 is characterized in that: In step S500, when the temperature of the base material is lower than 0°C, the preheating temperature is at least 50°C, and the working environment temperature at the beginning of welding should be higher than -20°C.

8. The 300-meter-deep water jacket S420 high-strength steel welding construction method according to claim 1 is characterized in that: In step S100, a cutting band is drawn on the S420 high-strength steel plate, and the entire steel plate is preheated. After preheating to the minimum required temperature, the entire steel plate is continuously heated, and a flame gun is used to heat along the cutting band, and then cutting is performed along the cutting band. After cutting is completed, the cutting band is covered with thermal insulation cotton, and the entire steel plate is continuously heated for a period of time before the heating is stopped.

9. The 300-meter-deep water jacket S420 high-strength steel welding construction method according to claim 1 is characterized in that: In step S500, after welding is completed, post-heat dehydrogenation treatment is performed before the temperature in the weld preheating area drops below 130°C. The post-heating temperature is maintained between 180°C and 210°C. The minimum post-heating time is 2 hours. When the parent material thickness T exceeds 50 mm, the post-heating time increases by 1 hour for every 25 mm increase in thickness. After the post-heat dehydrogenation is completed, insulation cotton is used for insulation, and the insulation time is 2 hours to 4 hours.

10. The 300-meter-deep water jacket S420 high-strength steel welding construction method according to claim 1 is characterized in that: After step S700, the qualified pipe sections are extended. During the extension, the annular seam is preheated and welded. When welding inside the pipe, after a period of welding, the operation is stopped and the weld is allowed to cool for a period of time before continuing welding.

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