A welding method for 420mpa high-pressure stainless steel pressure pipeline

Abstract

The application relates to a 420MPa high-pressure stainless steel pressure pipeline welding method, which comprises the following steps: groove processing; preheating before welding; backing welding; backing welding is carried out by adopting manual tungsten argon arc welding; filling and surface welding; argon arc welding is adopted to carry out filling layer and surface layer welding, wherein when the filling layer welding is carried out, the welding parameters include current 100-110A, voltage 11-13V, protective gas flow 10-20L / min, heat input 0.7-1.0kJ / mm and welding speed 70-80mm / min; when the surface layer welding is carried out, the welding parameters include current 95-100A, voltage 10.5-12.5V, protective gas flow 15-20L / min, heat input 0.6-0.9kJ / mm and welding speed 80-90mm / min; post-treatment: slow cooling after welding; during the welding process, the interlayer temperature is controlled to be less than or equal to 150 DEG C. The welding method is welded by adopting multi-layer multi-pass small heat input, the interlayer temperature is strictly controlled during the welding process, and a slow cooling process is combined, so that the mechanical properties and forming quality of the weld are greatly improved, welding defects are eliminated, and the welding joint can meet the long-term safe and stable operation requirements of 420MPa super-high pressure working conditions.

Description

Technical Field

[0001] This invention relates to the field of high-pressure pipeline welding technology, specifically to a welding method for a 420MPa high-pressure stainless steel pressure pipeline. Background Technology

[0002] 420MPa high-pressure stainless steel pipelines belong to ultra-high-pressure special equipment pipelines, with extremely high requirements for the sealing performance, mechanical strength, fatigue resistance, corrosion resistance, and structural stability of welded joints. Currently, most conventional stainless steel pipelines in the industry use single-layer argon arc welding or ordinary multi-layer welding processes, but these welding processes generally have the following shortcomings:

[0003] 1. Single-layer welding has a large heat input and concentrated residual stress in the weld. After the pipeline is under pressure, micro-cracks and deformation are likely to occur, and it cannot withstand the 420MPa ultra-high pressure load.

[0004] 2. In ordinary multi-layer welding, unreasonable layer arrangement and parameter mismatch can easily lead to defects such as incomplete root penetration, slag inclusions between layers, porosity, and lack of fusion, resulting in a low pass rate for non-destructive testing.

[0005] 3. Improper welding temperature control and excessively rapid cooling after welding lead to decreased weld toughness and reduced corrosion resistance, which can easily cause safety hazards such as leakage and cracking during long-term high-pressure operation;

[0006] 4. Conventional processes result in poor weld precision and excessive weld reinforcement, which can lead to stress concentration during high-pressure pipeline operation and shorten equipment lifespan.

[0007] These shortcomings mean that existing single-layer argon arc welding or ordinary multi-layer welding is only suitable for medium and low pressure pipeline conditions. Summary of the Invention

[0008] In view of this, the present invention provides a welding method for stainless steel pressure pipelines with a pressure of 420MPa, thereby solving or at least alleviating one or more of the above-mentioned problems and other problems existing in the prior art.

[0009] To achieve the aforementioned objectives, the technical solution adopted by the present invention is as follows:

[0010] A welding method for 420MPa high-pressure stainless steel pressure pipelines includes the following steps:

[0011] Beveling: Beveling is performed on pipes that need to be butt welded to create a V-shaped bevel and grinding both sides of the bevel.

[0012] Preheating before welding: Preheat the pipe welding area at a temperature of 110~130℃, with a preheating temperature rise of 50~80℃ / h.

[0013] Root pass welding: Manual tungsten inert gas welding is used for the root pass welding;

[0014] Filler and capping welding: Argon arc welding is used for welding the filler and capping layers, where,

[0015] When performing filler layer welding, the welding parameters include current 100-110A, voltage 11~13V, shielding gas flow rate 10-20L / min, heat input 0.7~1.0kJ / mm, and welding speed 70~80mm / min;

[0016] When performing capping layer welding, the welding parameters include current 95-100A, voltage 10.5~12.5V, shielding gas flow rate 15-20L / min, heat input 0.6~0.9kJ / mm, and welding speed 80-90mm / min;

[0017] Post-welding treatment: slow cooling after welding;

[0018] Throughout the entire welding process, the interpass temperature is controlled to be ≤150℃.

[0019] In the method described above, optionally, the welding parameters for the root pass include a current of 85-95A, a voltage of 10-12V, a shielding gas flow rate of 10-20L / min, a heat input of 0.65-0.95kJ / mm, and a welding speed of 85-95mm / min.

[0020] In the method described above, optionally, the pipe is made of 316L stainless steel or 304 stainless steel.

[0021] In the method described above, optionally, the protective gas is high-purity argon, and high-purity argon is used for protection throughout the welding process. The purity of the argon is greater than or equal to 99.99%, and the flow rate of the protective gas during the root pass is less than the flow rate during the fill pass, and the flow rate of the protective gas during the fill pass is less than the flow rate during the cover pass.

[0022] In the method described above, optionally, the root pass is a single-layer, single-pass weld, the filler layer is a multi-pass weld, and the cover layer is a single-pass weld.

[0023] In the method described above, optionally, the slow cooling is achieved by wrapping the item with insulating cotton.

[0024] In the method described above, optionally, the interlayer temperature is controlled at 80~150℃.

[0025] In the method described above, optionally, the welding wire for the root pass is ER316L (base material 316L) / ER308L (base material 304), the welding wire for the filler layer is ER316L (base material 316L) / ER308L (base material 304), and the welding wire for the cover pass is ER316L (base material 316L) / ER308L (base material 304).

[0026] In the method described above, optionally, the bevel is a V-shaped bevel with a blunt edge of 1.0-1.2mm, a root gap of 2.2-2.5mm, and the bevel is ground.

[0027] Optionally, in the method described above, the method further includes post-weld inspection to ensure that the weld tensile strength is above 420 MPa.

[0028] In this invention, the tensile strength of the weld is tested using a universal testing machine according to GB / T2651 Metallic Materials Tensile Testing Method.

[0029] Due to the application of the above-mentioned technical solution, the present invention has the following advantages compared with the prior art:

[0030] The welding method of the present invention uses multi-layer, multi-pass low heat input welding, and strictly controls the interpass temperature and combines it with a slow cooling process during the welding process, which greatly improves the mechanical properties and forming quality of the weld, eliminates welding defects, and enables the welded joint to meet the requirements for long-term safe and stable operation under 420MPa ultra-high pressure conditions. Detailed Implementation

[0031] Because existing welding processes are unsuitable for welding 420MPa high-pressure stainless steel pressure pipelines, the inventors of this application, through long-term research and extensive experimentation, discovered that by employing multi-layer, multi-pass low-heat-input welding combined with precise interpass temperature control and slow cooling processes, the mechanical properties and forming quality of the weld are significantly improved, welding defects are eliminated, and the welded joint fully meets the long-term safe and stable operation requirements under 420MPa ultra-high pressure conditions. Furthermore, this invention effectively solves the problems of numerous defects, high residual stress, insufficient mechanical properties, and easy leakage and cracking during high-pressure operation associated with traditional welding processes in ultra-high-pressure pipeline construction. It significantly improves weld forming quality, mechanical strength, and corrosion resistance, resulting in a high weld inspection pass rate, good process stability and repeatability. It can be widely applied to butt welding construction of ultra-high-pressure stainless steel pressure pipelines in the petroleum, chemical, and other fields, and is suitable for long-term high-pressure safe operation conditions.

[0032] One specific embodiment of the present invention is a welding method for 420MPa high-pressure stainless steel pressure pipelines, comprising the following steps:

[0033] S1. Beveling: Beveling is performed on the pipes that need to be butt welded, forming a V-shaped bevel and grinding both sides of the bevel;

[0034] In step S1, stainless steel pipes are selected as the base material for welding. The pipe material is 316L stainless steel or 304 stainless steel. High-purity argon gas is selected as the protective gas for the entire welding process, with a purity of greater than or equal to 99.99%.

[0035] In step S1, a V-shaped bevel is used, with a bevel angle of 30±2° (15±1° on one side), a blunt edge of 1.0-1.2mm, a root gap of 2.2-2.5mm, and 20mm of pipe wall on both sides of the bevel is ground to remove oxidized oil stains.

[0036] S2. Preheating before welding: Preheat the pipe welding area at a temperature of 110~130℃, with a preheating temperature rise of 50~80℃ / h.

[0037] In step S2, the preheating range is 50mm on both sides of the bevel.

[0038] S3. Root pass welding: The root pass welding is performed using manual tungsten inert gas welding.

[0039] In step S3, the root pass welding is performed using a single layer and single pass, and the welding wire is ER316L (base material 316L) / ER308L (base material 304).

[0040] In step S3, the welding parameters for the root pass include a current of 85-95A, a voltage of 10-12V, a shielding gas flow rate of 10-20L / min, a heat input of 0.65-0.95kJ / mm, and a welding speed of 85-95mm / min.

[0041] S4. Filling and capping welding: Argon arc welding is used for filling and capping welding.

[0042] In step S4, when welding the filler layer, the welding wire is ER316L (base material 316L) / ER308L (base material 304), and the welding parameters include current 100-110A, voltage 11~13V, shielding gas flow rate 10-20L / min, heat input 0.7~1.0kJ / mm, and welding speed 70~80mm / min;

[0043] In step S4, when welding the cover layer, the welding parameters include a current of 95-100A, a voltage of 10.5-12.5V, a shielding gas flow rate of 15-20L / min, a heat input of 0.6-0.9kJ / mm, and a welding speed of 80-90mm / min.

[0044] S5. Post-weld treatment: slow cooling after welding;

[0045] In step S5, slow cooling is achieved by wrapping the item in insulating cotton and slowly cooling it to room temperature.

[0046] S6. Post-weld inspection

[0047] In step S6, the welded joint after welding is tested according to GB / T2651, and the weld tensile strength must be above 420MPa.

[0048] During welding, the interpass temperature is controlled to ≤150℃. Further, the interpass temperature is controlled between 80~150℃. During welding, the shielding gas flow rate during the root pass is less than that during the fill pass, and the shielding gas flow rate during the fill pass is less than that during the cover pass.

[0049] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0050] Example 1

[0051] This embodiment provides a welding method for 420MPa high-pressure stainless steel pressure pipelines, including the following steps:

[0052] (1) Pre-welding preparation

[0053] The base material is 316L stainless steel with a wall thickness of 12mm, and high-purity argon gas is used for protection throughout the process. The argon gas purity is 99.9999%.

[0054] (2) Beveling

[0055] A V-shaped narrow-gap bevel is used, with a bevel angle of 30°, a root gap of 2.5mm, and a blunt edge of 1.2mm. The pipe wall on both sides of the bevel is ground for 20mm to remove oxide and oil contaminants. A stainless steel angle grinder with a stainless steel grinding wheel / flap wheel is used to grind the bevel and the 20mm pipe wall on both sides of the bevel until the metal luster is fully exposed, removing oxide scale, oil, and impurities from the pipe wall. Dedicated tools are used throughout the process; mixing carbon steel grinding tools is prohibited to avoid carburization and contamination of the weld.

[0056] (3) Preheating before welding

[0057] The pipe is preheated uniformly to 120℃ at a rate of 65℃ / h, and the preheating range is 50mm on both sides of the bevel.

[0058] Heating method: Flexible ceramic resistance heating strip / far-infrared heating device is used to uniformly heat the weld area of ​​the pipe;

[0059] Heating range: Based on the center of the weld bevel, the heating range extends 50mm on both sides of the bevel to completely cover the area.

[0060] Heating rate: The preheating temperature rise rate should be controlled at 65℃ / h, and the temperature should be raised slowly and uniformly. Local rapid high temperature should be prohibited.

[0061] Temperature control requirements: After uniformly raising the temperature to 120℃, hold the temperature for 5-10 minutes. Confirm that the temperature of the entire bevel area has stabilized in the range of 110-130℃ before starting welding.

[0062] Temperature measurement method: Multi-point temperature measurement using contact thermocouples is adopted to ensure uniform preheating temperature around the pipeline with no temperature difference.

[0063] 4) Manual tungsten inert gas welding for root pass

[0064] The root pass was performed using manual tungsten inert gas (TIG) welding in a single layer and single pass manner. The welding wire was ER316L Φ2.0mm. The welding parameters included: current 90A, voltage 11V, argon flow rate 14L / min, heat input 0.82kJ / mm, and welding speed 90mm / min.

[0065] (5) Welding of filler layer

[0066] Argon arc welding is used, and the welding is carried out in 3 passes. The welding wire is ER316L Φ2.0mm. The welding parameters include: current 105A, voltage 12V, argon flow rate 15L / min, heat input 0.88kJ / mm, interpass temperature control ≤150℃, and welding speed 75mm / min.

[0067] (6) Welding of the cover layer

[0068] Argon arc welding is used, single-pass welding, and ER316L Φ2.0mm welding wire is selected. The welding parameters include: current 100A, voltage 11.5V, argon flow rate 16L / min, heat input 0.75kJ / mm, and welding speed 85mm / min.

[0069] (7) Post-processing

[0070] After welding, wrap the product with insulating cotton and allow it to cool slowly to room temperature.

[0071] (8) Inspection

[0072] The weld is smooth, without spatter or defects, and passes UT and RT tests. The weld has a tensile strength of 565MPa, an impact energy of 45J, and no cracks in the bending test, fully meeting the requirements for 420MPa ultra-high pressure operation.

[0073] Example 2

[0074] The welding method for 420MPa high-pressure stainless steel pressure pipelines provided in this embodiment is basically the same as that in Embodiment 1, except that:

[0075] In step (1), the base material is 304 stainless steel with a wall thickness of 8mm.

[0076] In step (2), the bevel angle is 28°, the root gap is 2.2mm, and the blunt edge is 1.0mm.

[0077] In step (3), the temperature is preheated to 110°C at a rate of 55°C / h.

[0078] In step (4), the bottom layer current is 85A, the voltage is 10.5V, the argon flow rate is 13L / min, the heat input is 0.72kJ / mm, and the welding speed is 88mm / min.

[0079] In step (5), welding is performed in two passes with a current of 100A, a voltage of 11V, an argon flow rate of 14L / min, a heat input of 0.76kJ / mm, an interpass temperature control of ≤150℃, and a welding speed of 72mm / min.

[0080] In step (6), the current is 95A, the voltage is 10.8V, the argon flow rate is 15L / min, the heat input is 0.68kJ / mm, and the welding speed is 82mm / min.

[0081] The weld was smooth, without spatter or defects, and passed UT and RT tests. The weld tensile strength was 548MPa, the impact energy was 42J, and there were no cracks in the bending test, fully meeting the requirements for 420MPa ultra-high pressure operation.

[0082] Comparative Example 1

[0083] The stainless steel pressure pipe welding method provided in this comparative example is basically the same as that in Example 1, except that the argon flow rate for the root pass, filler layer and cover layer welding is 16 L / min.

[0084] Result: Continuous oxide inclusions appeared at the root of the weld, and the radiographic test determined it to be Grade II. The tensile strength of the weld was only 395MPa, which could not meet the 420MPa standard for use.

[0085] Comparative Example 2

[0086] The welding method for stainless steel pressure pipes provided in this comparative example is basically the same as that in Example 1, except that the interpass temperature is controlled at 200°C.

[0087] Results: The weld grains are coarse, with a significant tendency for intergranular corrosion. The impact energy at room temperature is only 26J. Microcracks appeared during fatigue testing, and there is a risk of leakage under long-term high pressure.

[0088] Comparative Example 3

[0089] The welding method for stainless steel pressure pipes provided in this comparative example is basically the same as that in Example 1, except that there is no slow cooling after welding, but natural cooling to room temperature is adopted instead.

[0090] Results: The residual stress in the weld increased significantly, microcracks appeared at the edge of the bending sample, the stress corrosion test failed, and it cannot be used under 420MPa ultra-high pressure conditions.

[0091] Compared with existing single-layer argon arc welding or ordinary multi-layer welding, the welding method involved in the embodiments of this application obviously has the following advantages:

[0092] 1) Adaptable to ultra-high pressure conditions: Specifically adapted to the operating load of 420MPa high-pressure stainless steel pipelines. Through multi-layer, multi-pass low heat input welding and inter-pass temperature control and slow cooling process, the residual stress of the weld is effectively reduced, avoiding weld cracking and leakage under high pressure conditions. The strength, toughness and fatigue resistance of the welded joint are greatly improved.

[0093] 2) Extremely low welding defect rate: The narrow gap bevel combined with the precise layered welding of root pass, fill pass, and cover pass completely solves common defects such as incomplete root penetration, slag inclusions between layers, porosity, and lack of fusion. The first pass rate of UT and RT non-destructive testing can reach more than 99%.

[0094] 3) Excellent overall performance of welds: High-purity argon gas is used for full protection, the welds are free from oxidation and have good corrosion resistance. The slow cooling process after welding refines the metallographic structure of the welds, improves the overall mechanical properties of the joints, meets the long-term service requirements of ultra-high pressure pipelines, and extends the service life of equipment.

[0095] 4) Highly practical for construction: The process is simple to operate, the shape is beautiful, the amount of grinding after welding is small, reducing construction costs. It is suitable for butt welding of high-pressure stainless steel pipes of various wall thicknesses and materials, and has a wide range of applications.

[0096] 5) Strong process stability: The interpass temperature, welding current, argon flow rate and welding speed are precisely controllable, avoiding human operation errors, and can be replicated in batches, making it suitable for industrial-scale high-pressure pipeline welding operations.

[0097] 6) The welding method of this invention is specifically adapted to 420MPa ultra-high pressure stainless steel pipelines, which is different from the existing medium and low pressure welding process and fills the gap in the multi-layer and multi-pass argon arc welding process for ultra-high pressure pipelines.

[0098] 7) By combining high-purity argon protection and slow cooling process, the metallographic structure of the weld is refined, taking into account the weld strength, toughness and corrosion resistance, so as to meet the long-term service standards of ultra-high pressure.

[0099] The above embodiments are only used to illustrate the embodiments of the present invention, and are not intended to limit the embodiments of the present invention. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the embodiments of the present invention. Therefore, all equivalent technical solutions also fall within the scope of the embodiments of the present invention, and the patent protection scope of the embodiments of the present invention should be defined by the claims.

Claims

1. A welding method for 420MPa high-pressure stainless steel pressure pipelines, characterized in that, The method includes the following steps: Beveling: Beveling is performed on pipes that need to be butt welded to create a V-shaped bevel and grinding both sides of the bevel. Preheating before welding: Preheat the pipe welding area at a temperature of 110~130℃, with a preheating temperature rise of 50~80℃ / h. Root pass welding: Manual tungsten inert gas welding is used for the root pass welding; Filler and capping welding: Argon arc welding is used for welding the filler and capping layers, where, When performing filler layer welding, the welding parameters include current 100-110A, voltage 11~13V, shielding gas flow rate 10-20L / min, heat input 0.7~1.0kJ / mm, and welding speed 70~80mm / min; When performing capping layer welding, the welding parameters include current 95-100A, voltage 10.5~12.5V, shielding gas flow rate 15-20L / min, heat input 0.6~0.9kJ / mm, and welding speed 80-90mm / min; Post-welding treatment: slow cooling after welding; Throughout the entire welding process, the interpass temperature is controlled to be ≤150℃.

2. The method according to claim 1, characterized in that, The welding parameters for the root pass include a current of 85-95A, a voltage of 10-12V, a shielding gas flow rate of 10-20L / min, a heat input of 0.65-0.95kJ / mm, and a welding speed of 85-95mm / min.

3. The method according to claim 1, characterized in that, The pipe is made of 316L stainless steel or 304 stainless steel.

4. The method according to claim 1, characterized in that, The protective gas is high-purity argon, and high-purity argon is used for protection throughout the welding process. The purity of the argon is greater than or equal to 99.99%, and the flow rate of the protective gas during the root pass is less than that during the fill pass, and the flow rate of the protective gas during the fill pass is less than that during the cover pass.

5. The method according to claim 1, characterized in that, The root pass is a single-layer, single-pass weld, the filler layer is a multi-pass weld, and the top pass is a single-pass weld.

6. The method according to claim 1, characterized in that, The slow cooling process involves wrapping the item in insulating cotton.

7. The method according to claim 1, characterized in that, The interlayer temperature is controlled at 80~150℃.

8. The method according to claim 1, characterized in that, The welding wire used for the root pass is ER316L or ER308L, the welding wire used for the filler layer is ER316L or ER308L, and the welding wire used for the cover pass is ER316L or ER308L.

9. The method according to claim 1, characterized in that, The bevel adopts a V-shaped bevel with a blunt edge of 1.0-1.2mm and a root gap of 2.2-2.5mm. The bevel is ground.

10. The method according to claim 1, characterized in that, The method also includes post-weld inspection to ensure that the weld tensile strength is above 420 MPa.