CN113798718A - Process method for welding liquefied natural gas pipeline without back shielding gas - Google Patents
Process method for welding liquefied natural gas pipeline without back shielding gas Download PDFInfo
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- CN113798718A CN113798718A CN202111294890.8A CN202111294890A CN113798718A CN 113798718 A CN113798718 A CN 113798718A CN 202111294890 A CN202111294890 A CN 202111294890A CN 113798718 A CN113798718 A CN 113798718A
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- welding
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- pipeline
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K31/00—Processes relevant to this subclass, specially adapted for particular articles or purposes, but not covered by only one of the preceding main groups
- B23K31/02—Processes relevant to this subclass, specially adapted for particular articles or purposes, but not covered by only one of the preceding main groups relating to soldering or welding
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K28/00—Welding or cutting not covered by any of the preceding groups, e.g. electrolytic welding
- B23K28/02—Combined welding or cutting procedures or apparatus
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K2101/00—Articles made by soldering, welding or cutting
- B23K2101/04—Tubular or hollow articles
- B23K2101/10—Pipe-lines
Abstract
The invention discloses a process method for welding a liquefied natural gas pipeline without back shielding gas, which comprises the following steps: s1: selecting the type of the welding material with the deoxidation performance; s2: processing and assembling a pipeline groove; s3: filling front protective gas without back protective gas; s4: welding under the condition of avoiding filling back protective gas; the invention has the advantages of no back protection gas filling, saving of gas filling protection time and gas, contribution to construction personnel safety, high construction efficiency, low labor intensity and the like, and is particularly suitable for a liquefied natural gas stainless steel pipeline system which is dried at a low temperature of-196 ℃ and is in service, such as: liquefied natural gas system, dry cooling liquid discharge system, defrosting gas system, mixed refrigerant system, non-condensable steam system and the like.
Description
Technical Field
The invention relates to a welding process method of a liquefied natural gas pipeline system, in particular to a process method for welding a liquefied natural gas pipeline without a back protection gas.
Background
Liquefied Natural Gas (LNG) is a liquid obtained by compressing and cooling Natural Gas to its condensation point (-161.5 ℃), and has methane as a main component, which is known as the cleanest fossil energy on earth. It is colorless, odorless, non-toxic and non-corrosive, and many pipeline systems for producing and storing liquefied natural gas are designed to be in service at low temperatures, typically up to-196 ℃, where some of the fluid medium in the pipeline system is purely dry, free of moisture, and free of corrosive media.
The stainless steel pipeline of the LNG (liquefied natural gas) project is mainly made of 304L or 316L stainless steel, and as the stainless steel material has higher alloy elements, the current construction method at home and abroad is as follows: in the process of welding the stainless steel pipeline, inert gases such as argon gas and the like need to be filled into the stainless steel pipeline for protection, so that the burning loss or excessive oxidation of alloy elements at the joint position caused by high welding temperature is prevented. The process of filling the back protective gas usually needs to occupy relatively long time, manpower and gas investment, the inert gas is colorless and odorless, the inert gas filled into the large-size pipeline can increase certain safety risk, and oxygen deficiency or suffocation accidents of people caused by the inert gas are caused at home and abroad.
At present, no process method suitable for welding the liquefied natural gas stainless steel pipeline system without the back shielding gas is available in China. The existing stainless steel pipeline system needs to be filled with inert gas to protect a root welding area, argon arc welding is adopted to weld backing welding and hot welding, and filling welding and cover welding adopt required technological methods according to different working conditions.
The welding industry has been trying to solve this problem by optimizing the process innovation or optimizing the auxiliary tools, and until now, no reliable method has been found that can completely replace the back protection with inert gas.
Disclosure of Invention
The technical problem to be solved by the invention is to provide a process method for protecting the back without filling inert gas when welding a liquefied natural gas pipeline.
In order to solve the technical problem, the invention provides a process method for welding a liquefied natural gas pipeline without a back shielding gas, which comprises the following steps of:
s1: and (3) welding material selection of the deoxidation performance: high-silicon solid welding wires are selected for backing welding and hot welding, and high-silicon solid welding wires, flux-cored welding wires or solid welding wires are selected for filling welding and cover welding;
s2: processing and assembling a pipeline groove: adopting a 35-40-degree groove with two opposite sides or adopting a double-side composite groove;
s3: the pipeline slope is filled with front protective gas without back protective gas;
s4: backing welding, hot welding, filling welding and cover welding are carried out on the pipeline at the groove: the backing welding adopts the gas metal arc welding of a short circuit transition mode, and the hot welding adopts the gas metal arc welding of a pulse transition mode; the filling welding and the cover welding adopt a consumable electrode gas shielded welding process, a flux-cored wire gas shielded welding process or a mechanical submerged arc welding process, and multilayer and multi-pass welding is adopted to finish the welding.
According to one embodiment of the invention, the pipeline is a liquefied natural gas stainless steel pipeline in low-temperature dry service.
According to an embodiment of the invention, in the step S2, the wall thickness of the pipeline is less than or equal to 22mm, and grooves of 35-40 degrees are split oppositely on two sides; the wall thickness is larger than 22mm, and a double-sided composite groove is adopted.
According to an embodiment of the invention, in the step S2, the groove machining is performed by adopting a machining mode or a combined machining and polishing mode, after the integrity of the groove and the adjacent area is ensured, the groove assembly is performed, the gap of the groove assembly is 3-5 mm, and the groove surface and external impurities on two sides of the weld joint are polished and removed.
According to an embodiment of the present invention, in the step S3, a mixture of argon and carbon dioxide is used as the front shielding gas for the backing welding and the hot welding, and a mixture of argon and carbon dioxide or pure carbon dioxide is used as the front shielding gas for the filling welding and the cover welding.
According to an embodiment of the present invention, in step S4, when the vertical welding is adopted as the backing welding, the welding direction is vertical downward welding; when the vertical welding is adopted for the hot welding, the welding direction is vertical upward welding.
According to an embodiment of the invention, in the step S4, the short-circuit transition mode of the gas metal arc welding parameters used in the backing welding are set to be 70-95A of welding current, 14-18V of welding voltage, 70-150 mm/min of welding speed, and the welding heat input is controlled to be 0.6-0.9 kJ/mm.
According to an embodiment of the present invention, in the step S4, the parameters of the gas metal arc welding in the pulse transition mode for the thermal welding are set to be 75-100A of welding current, 16-20V of welding voltage, 70-150 mm/min of welding speed, and the input of welding heat is controlled to be 0.6-1.1 kJ/mm.
According to an embodiment of the invention, in the step S4, the welding current of the gas metal arc welding used for the filling welding and the cover welding is 75-100A, the welding voltage is 16-20V, and the welding speed is 70-150 mm/min.
According to an embodiment of the invention, in the step S4, the welding current of the flux-cored wire gas shielded welding used in the filling welding and the cover surface welding is 130-200A, the welding voltage is 25-30V, the welding speed is 130-200 mm/min, and the heat input is controlled to be 1.3-2.0 kJ/mm; the welding current of the mechanical submerged arc welding is 300-430A, the welding voltage is 26-33V, the welding speed is 330-500 mm/min, and the heat input is controlled to be 1.4-2.2 kJ/mm.
The invention has the technical effects that:
1. the invention reduces the oxidation degree of the welding joint area of the liquefied natural gas pipeline to a very low level by adopting the gas metal arc welding, the technique method and the welding skill with lower welding heat input and using the welding material with certain deoxidation performance, thereby realizing the beneficial effect of welding the liquefied natural gas pipeline under the condition of avoiding filling inert gas for back protection.
2. The process of filling the back protection gas usually needs to occupy more time, labor and gas investment, and the invention realizes the welding of the back protection gas without filling by reducing the oxidation degree of the joint area of the natural gas pipeline, thereby saving the time and the gas for carrying out the gas filling protection.
3. The large-size pipeline is filled with inert gas, certain safety risk is increased, personnel are easy to lack oxygen or suffocate accidents, and the personnel safety in the construction stage is facilitated by welding the liquefied natural gas pipeline under the condition of avoiding filling the inert gas for back protection.
Drawings
FIG. 1 is a design drawing of a double-sided split groove of a liquefied natural gas pipeline back-shielding-gas-free welding process of the present invention;
FIG. 2 is a design drawing of a double-sided composite groove of the liquefied natural gas pipeline back-shielding-free gas welding process method.
Detailed Description
The present invention is further described with reference to the following drawings and specific examples so that those skilled in the art can better understand the present invention and can practice the present invention, but the examples are not intended to limit the present invention.
As shown in figure 1, the wall thickness of the pipeline is less than or equal to 22mm, and a 37.5-degree groove is formed by two sides in a split mode.
As shown in figure 2, the wall thickness of the pipeline is more than 22mm, and a double-sided compound groove is adopted.
The process method for welding the liquefied natural gas stainless steel pipeline in service with the low-temperature drying medium without back shielding gas is characterized in that the pipeline system is suitable for drying the liquefied natural gas stainless steel pipeline in service at the low temperature of-196 ℃, such as: the system comprises a liquefied natural gas system, a dry-cold liquid discharge system, a defrosting gas system, a mixed refrigerant system, a non-condensable vapor system and the like, and the pipeline is made of 304 or 316 stainless steel.
In the step S1, the high-silicon welding material selection is to select a corresponding welding material according to the principle of matching the chemical components of the base metal and the welding material, and AWS A5.9 ER308LSi/ER316Lsi high-silicon solid welding wire is used for backing welding and hot welding, wherein the content of silicon element is more than or equal to 0.65% and less than or equal to 0.9%, and the diameter of the welding wire is 0.9 mm; the welding materials of the filling welding and the cover surface welding can be high-silicon solid core welding materials, or GFS-308L or GFS-316L flux-cored wires and GWS-308L or GWS-316L submerged arc welding wires matched with GWS-300 welding flux; the shielding gas for both backing and hot welding was a 98% argon (Ar) and 2% carbon dioxide (CO2) mixture.
In step S2, groove designing: the wall thickness of the pipeline is less than or equal to 22mm, and a groove with 35-40 degrees is split on two sides; the wall thickness is larger than 22mm, and a double-sided composite groove is adopted. Groove preparation: and machining the groove according to a design drawing by adopting a machining mode. Groove assembling: and (3) checking the groove processing quality, and performing groove assembly after ensuring the integrity of the groove and the adjacent area, wherein the gap of the groove assembly is 3-5 mm. Cleaning a groove: and grinding to remove the bevel face and external impurities on two sides of the welding line.
In the step S2, the angle of the groove after butt welding and hot welding area pairing is 75 +/-5 degrees, the butt edge of the root is 0-1 mm, and the gap of the groove is 3-5 mm; the groove is manufactured by adopting a machining method or a method of combining machining and polishing; before welding, the bevel face and external impurities such as oil, rust, sand, splash and the like within the range of 25mm on two sides of the welding line are polished to be removed.
In the step S3, a mixture of 98% argon (Ar) and 2% carbon dioxide (CO2) is used as a front shielding gas for the backing welding and the hot welding, and a mixture of 98% argon and 2% carbon dioxide or pure carbon dioxide is used as a front shielding gas for the filling welding and the cover welding; no back shielding gas is used in the welding process.
In the step S4, the welding method selected for backing welding and hot welding is fixed, backing welding must be performed by gas metal arc welding in a short circuit transition mode with controlled output, the welding current can be reduced to an extremely low level at the moment when the molten drop is about to explode in the short circuit transition process, smooth transition of molten metal is realized, good double-sided forming of single-sided welding is obtained, welding spatter can be reduced to the maximum extent, if vertical welding is required, the welding direction must be vertical downward welding, hot welding must be gas metal arc welding in a pulse transition mode, and if vertical welding is required, the welding direction is vertical upward welding.
In the step S4, in the welding process of backing welding and hot welding under the condition of avoiding back shielding gas filling, short-circuit transition consumable electrode gas shielded welding is adopted for backing welding, the vertical welding direction is vertical downward welding, the angle between a welding gun and the outer surface of the pipeline is 10-15 degrees, the welding gun controls the molten pool at the front end of the electric arc and the molten pool at the dragging angle, and the position of the center of the electric arc at the front end of the whole molten pool is kept at 2-3 mm. The backing welding parameters are set to be 70-95A of welding current, 14-18V of welding voltage and 70-150 mm/min of welding speed, the front-side welding protective gas is a mixture of 98% argon (Ar) and 2% carbon dioxide (CO2), the gas flow is 15-20L/min, and attention should be paid to the backing welding process: the vertical welding direction is vertical downward welding, the root gap of the overhead welding position (namely, the position of the positive six points) is controlled not to exceed 4mm, in the actual operation process, the lower half part of the circular seam of the pipe can be welded firstly, for example, the positions of 5 to 7 points, the welding operation difficulty at the overhead welding position caused by the welding shrinkage of root welding is avoided, the welding pause is not required to occur at the position of the positive six points, and the root welding joint is avoided; the hot welding adopts pulse transition consumable electrode gas shielded welding, welding parameters are set to be 75-100A of welding current, 16-20V of welding voltage, 70-150 mm/min of welding speed, the welding heat input of backing welding is controlled to be 0.6-0.9kJ/mm, the welding heat input of hot welding is controlled to be 0.6-1.1kJ/mm, and after the backing welding and the hot welding are completed, the thickness of a welding seam is ensured to be at least more than or equal to 6.5 mm.
In the filling welding and cover surface welding process under the condition of avoiding back shielding gas filling in the step S4, the welding current of the gas metal arc welding is 75-100A, the welding voltage is 16-20V, and the welding speed is 70-150 mm/min; the welding current of the flux-cored wire gas shielded welding is 130-200A, the welding voltage is 25-30V, the welding speed is 130-200 mm/min, the shielding gas is carbon dioxide, and the heat input is controlled to be 1.3-2.0 kJ/mm; the welding current of the mechanical submerged arc welding is 300-430A, the welding voltage is 26-33V, the welding speed is 330-500 mm/min, and the heat input is controlled to be 1.4-2.2 kJ/mm.
The steps are combined conditions for realizing the back-free shielding gas welding of the stainless steel pipeline system, and the key points are root welding and hot welding process methods, welding parameters and technical points, the obtained welding joint can be suitable for the liquefied natural gas stainless steel pipeline system which is dried at the low temperature of-196 ℃ and is in service, such as: liquefied natural gas system, dry cooling liquid discharge system, defrosting gas system, mixed refrigerant system, non-condensable steam system and the like.
The above-mentioned embodiments are merely preferred embodiments for fully illustrating the present invention, and the scope of the present invention is not limited thereto. The equivalent substitution or change made by the technical personnel in the technical field on the basis of the invention is all within the protection scope of the invention. The protection scope of the invention is subject to the claims.
Claims (10)
1. A process method for welding liquefied natural gas pipelines without back shielding gas is characterized by comprising the following steps:
s1: and (3) welding material selection of the deoxidation performance: high-silicon solid welding wires are selected for backing welding and hot welding, and high-silicon solid welding wires, flux-cored welding wires or solid welding wires are selected for filling welding and cover welding;
s2: processing and assembling a pipeline groove: adopting a 35-40-degree groove with two opposite sides or adopting a double-side composite groove;
s3: the pipeline slope is filled with front protective gas without back protective gas;
s4: backing welding, hot welding, filling welding and cover welding are carried out on the pipeline at the groove: the backing welding adopts the gas metal arc welding of a short circuit transition mode, and the hot welding adopts the gas metal arc welding of a pulse transition mode; the filling welding and the cover welding adopt a consumable electrode gas shielded welding process, a flux-cored wire gas shielded welding process or a mechanical submerged arc welding process, and multilayer and multi-pass welding is adopted to finish the welding.
2. The welding process of claim 1, wherein the pipeline is a cryogenically dried lng stainless steel pipeline.
3. The liquefied natural gas pipeline back-shielding-free gas welding process method as claimed in claim 1, wherein in step S2, the pipeline wall thickness is less than or equal to 22mm, and grooves with 35-40 degrees are split oppositely; the wall thickness is larger than 22mm, and a double-sided composite groove is adopted.
4. The liquefied natural gas pipeline back-shielding-gas-free welding process method according to claim 1, wherein in the step S2, groove machining is performed in a machining mode or a combined machining and grinding mode, after the integrity of the groove and the area nearby the groove is ensured, groove assembly is performed, the gap between the groove assembly is 3-5 mm, and external impurities on the groove surface and the two sides of the welding seam are removed by grinding.
5. The liquefied natural gas pipeline back-shielding-gas-free welding process as claimed in claim 1, wherein in step S3, a mixture of argon and carbon dioxide is used as the front shielding gas for backing welding and thermal welding, and a mixture of argon and carbon dioxide or pure carbon dioxide is used as the front shielding gas for filling welding and cover welding.
6. The liquefied natural gas pipeline back-shielding-gas-free welding process method as claimed in claim 1, wherein in the step S4, when the backing weld is a vertical weld, the welding direction is a vertical downward weld; when the vertical welding is adopted for the hot welding, the welding direction is vertical upward welding.
7. The liquefied natural gas pipeline back-shielding-gas-free welding process method as claimed in claim 1, wherein in step S4, the short-circuit transition mode of the gas metal arc welding parameters for backing welding are set to welding current of 70-95A, welding voltage of 14-18V, welding speed of 70-150 mm/min, and welding heat input is controlled to be 0.6-0.9 kJ/mm.
8. The method for welding liquefied natural gas pipelines without using shielding gas as claimed in claim 1, wherein in step S4, the parameters of the pulse transition mode for the gas metal arc welding are set to welding current 75-100A, welding voltage 16-20V, welding speed 70-150 mm/min, and welding heat input is controlled to 0.6-1.1 kJ/mm.
9. The liquefied natural gas pipeline back-shielding-gas-free welding process method as claimed in claim 1, wherein in step S4, the welding current of the gas metal arc welding used in the filling welding and the cover welding is 75-100A, the welding voltage is 16-20V, and the welding speed is 70-150 mm/min.
10. The liquefied natural gas pipeline back-shielding-gas-free welding process method as claimed in claim 1, wherein in step S4, the welding current of flux-cored wire gas shielded welding used in fill welding and cover surface welding is 130-200A, the welding voltage is 25-30V, the welding speed is 130-200 mm/min, and the heat input is controlled to be 1.3-2.0 kJ/mm; the welding current of the mechanical submerged arc welding is 300-430A, the welding voltage is 26-33V, the welding speed is 330-500 mm/min, and the heat input is controlled to be 1.4-2.2 kJ/mm.
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| CN202111294890.8A CN113798718A (en) | 2021-11-03 | 2021-11-03 | Process method for welding liquefied natural gas pipeline without back shielding gas |
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| CN202111294890.8A CN113798718A (en) | 2021-11-03 | 2021-11-03 | Process method for welding liquefied natural gas pipeline without back shielding gas |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN114713938A (en) * | 2022-03-29 | 2022-07-08 | 奥特(南京)智能制造有限公司 | Automatic priming process method for process pipeline robot |
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2021
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