A combined groove welding process for thin-walled super duplex stainless steel

Abstract

The present invention discloses a thin-walled super duplex stainless steel combined groove welding process, belonging to the field of stainless steel welding technology, comprising the following steps: S1, processing a groove on the super duplex stainless steel joint to be welded, wherein the groove angle is 30°±2.5°, the blunt edge height is 0.5-0.8mm, the step length is 0.8-1.5mm, and a circular arc angle of R1-2mm is processed at the intersection of the blunt edge and the bevel edge of the groove; S2, assembling the super duplex stainless steel joints to be welded with the grooves; S3, welding is performed using tungsten inert gas arc welding in a pulsed manner; and S4, welding is performed using multiple layers and multiple passes. The present invention has a small welding torch swing during the bottom sealing process, and the groove angle can be well fused without large swing. The bottom sealing welding time is short, the operation is simple when using the groove, and a good root forming is easily achieved. The zero gap of the combined groove can effectively control the bottom sealing weld bead height on the back of the weld to be less than 1.5mm.

Description

Technical Field

[0001] The invention belongs to the technical field of stainless steel welding, and in particular relates to a combined groove welding process for thin-walled super duplex stainless steel. Background Art

[0002] UNS S32750 super duplex stainless steel, based on ordinary duplex stainless steel, increases the content of molybdenum and nitrogen trace elements. Compared with ordinary duplex stainless steel, it has superior corrosion resistance and can be used in more severe corrosive environments. The higher content of alloying elements and lower carbon content give the material stronger mechanical properties during service. It is increasingly used in submarine pipeline laying, shipbuilding, and offshore gas field production, which require high strength and high corrosion resistance. Especially in pressure vessels and heat exchangers containing chloride ions and hydrogen sulfide media.

[0003] Typically, V-grooves are used for welding. However, for small-diameter and thin-walled pipes under 2 inches and with wall thicknesses of 1.65mm to 5.55mm, welding is difficult and inefficient due to the small diameter, thin wall, and rapidly changing welding angles. This can also easily lead to defects such as undercuts, lack of fusion, and weld bumps. Furthermore, the gap-retained groove assembly requires certain bridging techniques for positioning welding tools, which requires high welder skills. The back seal weld is welded at the 12 o'clock position, as the back inflation creates upward pressure, which can lead to a concave root if not handled with care.

[0004] Currently, the quality control methods for super duplex stainless steel small pipeline welding are: first, improve the quality of the assembly to lay the foundation for welding quality; second, improve the welder's skills, adopt multi-layer and multi-pass welding, and strictly control the inter-layer temperature.

[0005] However, due to factors such as the construction environment, welding materials, and welder skill level, V-groove welding is prone to defects such as undercuts and excessive reinforcement. Furthermore, due to the large amount of filler metal, when manual welding uses wedges for positioning, if foreign matter falls into the pipeline when the wedges are ground off during the bottom welding process and is not cleaned up in time, the complex curved pipeline cannot be effectively cleaned of all debris during the final purge process, affecting the post-cleaning and pressure testing. Using wire to bridge the groove requires the welder to have excellent bridging skills, and the groove gaps vary in size, resulting in uneven reinforcement at the root of the back after the base is penetrated. Even the best welders cannot guarantee a qualified weld every time.

[0006] Therefore, it is urgent to design a thin-walled super duplex stainless steel combined groove welding process to solve the above-mentioned problems. Summary of the Invention

[0007] The purpose of the present invention is to provide a thin-walled super duplex stainless steel combined groove welding process, which has the advantages of reducing the difficulty of welder operation, improving welding quality, and reducing construction costs, thereby solving the problems mentioned in the background technology.

[0008] To achieve the above objectives, the specific technical solution of the thin-walled super duplex stainless steel combined groove welding process of the present invention is as follows:

[0009] A thin-walled super duplex stainless steel combined groove welding process comprises the following steps:

[0010] S1. Process a groove on the super duplex stainless steel joint to be welded, with a groove angle of 30°±2.5°, a blunt edge height of 0.5-0.8mm, a step length of 0.8-1.5mm, and a circular arc angle of R1-2mm at the junction of the blunt edge and the bevel edge of the groove;

[0011] S2. Assemble the super duplex stainless steel welded joints with grooves processed thereon;

[0012] S3, welding is performed using tungsten inert gas arc welding in the form of pulses;

[0013] S4. Use multi-layer and multi-pass welding.

[0014] Furthermore, in S1, the groove is processed by a machining method.

[0015] Furthermore, after groove processing, the weld area and the area 50 mm away from the groove were cleaned with a stainless steel grinding wheel to remove debris.

[0016] Furthermore, in S2, the gap between the pairs of super duplex stainless steel welded joints with grooves processed is 0 mm.

[0017] Furthermore, in S3, small heat input welding is adopted during the welding process, the welding gun base current is 30-42A, the peak current is 50-72A, the base voltage is 8-10V, the peak voltage is 10-12V, and the welding speed is 2-5cm / min.

[0018] Furthermore, the shielding gas in the welding gun is a high-purity argon-nitrogen mixture, and the shielding gas at the weld root is pure nitrogen.

[0019] Furthermore, when tungsten inert gas arc welding is used for welding in a pulsed manner, effective discharges occur five times on the discharge gap per unit time.

[0020] Furthermore, in S4, the thickness of each weld layer is not higher than 2 mm, and the temperature between layers is not higher than 100°C.

[0021] Furthermore, after each layer of welding is completed, the weld should be cooled immediately with an air gun, and the compressed air used by the air gun should be dried in a dryer before use.

[0022] Furthermore, all welding is vertical upward welding, and the filling cover welding is composed of left and right cross vertical upward welding.

[0023] The present invention has the following advantages: the welding process is simple to operate, and the groove design is novel. It meets the characteristics of being difficult to control the height of the back weld bead of thin-walled welding joints with a wall thickness of 1.65mm to 5.55mm and less than 2 inches, and the welding angle of the small pipe changes quickly. The welding gun swings slightly when sealing the bottom, and the angle of the groove can be fused well without too much swing. The time for bottom welding is short. The operation is simple when using this groove, and it is easy to obtain a better root forming. By combining the groove with zero gap, the residual height of the bottom weld bead on the back of the weld can be effectively controlled to be less than 1.5mm. The 0mm gap group of the groove can solidify the operating techniques of the welder, making it easy to master, reducing the operating difficulty of the construction personnel, improving the welding quality, and reducing the construction cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The schematic diagram of the combined welding structure of the thin-walled super duplex stainless steel joint of the present invention Figure 1 ;

[0025] Figure 2 The schematic diagram of the combined welding structure of the thin-walled super duplex stainless steel joint of the present invention Figure 2 ;

[0026] Explanation of the marks in the figure: 1, super duplex stainless steel joint to be welded; 11, arc corner; 12, blunt edge; 13, step; 14, groove. DETAILED DESCRIPTION

[0027] To make the purpose, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making any creative efforts shall fall within the scope of protection of the present invention.

[0028] Those skilled in the art will appreciate that although some embodiments herein include certain features included in other embodiments but not other features, the combination of features from different embodiments is intended to be within the scope of the present invention and to form different embodiments. For example, in the claims, any one of the claimed embodiments may be used in any combination.

[0029] Please refer to the attached Figure 1 To the attached Figure 2 The present invention describes a thin-wall super duplex stainless steel combined groove welding process.

[0030] Super duplex stainless steel is 2507 super duplex stainless steel composed of 25.52% chromium, 3.58% molybdenum, and 6.2% nickel.

[0031] Currently, V-groove welding is prone to defects such as undercutting and excessive reinforcement during construction, due to factors such as the construction environment, welding materials, and welder skill level. Furthermore, due to the large amount of filler metal, when manual welding uses wedges for positioning, if foreign matter falls into the pipeline when the wedges are ground off during the backing welding process and is not promptly cleaned, the complex curved pipeline cannot be effectively cleaned of all debris during the final purge, affecting the post-cleaning and pressure testing. Using wire to bridge the groove requires welders to have excellent bridging skills, and the groove gaps vary in size, resulting in uneven reinforcement at the root of the backing after the base is penetrated. Even the best welders cannot guarantee a qualified weld every time.

[0032] Therefore, the method includes the following steps:

[0033] S1. Processing a groove 14 of the super duplex stainless steel to be welded joint 1, wherein the angle of the groove 14 is 30°±2.5°, the height of the blunt edge 12 is 0.5-0.8 mm, the length of the step 13 is 0.8-1.5 mm, and an arc angle 11 of R1-2 mm is processed at the intersection of the blunt edge 12 and the bevel of the groove 14;

[0034] Preferably, the groove 14 is processed by mechanical processing. In other embodiments of the present invention, other processing methods can also be used as long as the size of the groove 14 can be met.

[0035] By setting the groove 14 angle to 30°±2.5°, after the duplex stainless steel welded joints are assembled, the combined groove 14 angle is 60°±5°, thereby controlling the weld bead formation and adjusting the groove 14 angle according to the pipeline wall thickness.

[0036] By setting the height of the blunt edge 12 of the groove 14 to 0.5-0.8 mm, it is ensured that the first layer of bottom sealing weld is welded through.

[0037] By setting the length of the step 13 of the groove 14 to 0.8 to 1.5 mm, combined with the height of the blunt edge 12, it is prevented that the parent material is burned through when welding the first layer of the bottom seal.

[0038] By setting the arc angle 11 in the groove 14 to R1-2 mm, the angle of the groove 14 is well fused during welding.

[0039] Use ER2594 welding wire with a diameter of 0.8 as the weld filler metal. Keep the welding wire clean and do not expose it to the atmosphere.

[0040] Preferably, the chemical composition of ER2594 welding wire is: C 0.014%, Mn 0.37%, Si 0.41%, S 0.0007%, P 0.02%, Ni 9.50%, Mo 3.9%, Cr 24.8%.

[0041] After processing groove 14, use a stainless steel grinding wheel to clean the weld area and the area 1450mm away from the groove to remove debris.

[0042] Debris includes oil, water or rust etc.

[0043] The duplex stainless steel joint to be welded needs to be cleaned with acetone or methanol before welding.

[0044] S2, assembling a group of super duplex stainless steel welded joints with grooves 14 processed thereon;

[0045] Preferably, the super duplex stainless steel to be welded joint 1 with the groove 14 processed has a pair gap of 0 mm. If there is a local gap during assembly, the groove 14 should be repaired until the combined gap is 0 mm. The misalignment of the assembly is controlled below 0.5 mm to avoid defects such as root incomplete fusion.

[0046] S3, welding is performed using tungsten inert gas arc welding in the form of pulses;

[0047] During the welding process, small heat input welding is adopted, the base current of the welding gun is 30-42A, the peak current is 50-72A, the base voltage is 8-10V, the peak voltage is 10-12V, and the welding speed is 2-5cm / min.

[0048] The shielding gas in the welding gun is a high-purity argon-nitrogen mixture, a mixture of argon (98%) and nitrogen (2%), with a purity of 99.999% and a gas flow rate of 15-25L / min. The shielding gas at the root of the weld is pure nitrogen, with a purity of 99.999% and a gas flow rate of 15-20L / min.

[0049] When tungsten inert gas welding is performed in the form of pulses, effective discharges occur 5 times on the discharge gap per unit time, and a 220V inverter DC tungsten inert gas welding machine is used.

[0050] S4. Use multi-layer and multi-pass welding.

[0051] Preferably, the thickness of each weld seam is not higher than 2 mm, and the temperature between layers is not higher than 100°C.

[0052] After each layer of welding is completed, the weld should be cooled immediately with an air gun. The compressed air used in the air gun should be dried in a dryer before use.

[0053] Preferably, the dryer is RC-100A, which can process an air volume of 13m³ / min.

[0054] In a preferred embodiment of the present invention, the welding is all vertical welding, and the filling and capping welding is composed of left and right cross vertical welding.

[0055] The super duplex stainless steel material obtained by this groove welding process has good weld fusion, uniform weld back penetration height, good forming, no welding defects, good welding quality, and the mechanical properties and corrosion resistance of the welded joint meet the standards and usage requirements.

[0056] This thin-walled super duplex stainless steel combined groove welding process features simple operation and a novel groove design, meeting the requirements of small tubes and thin walls. The welding torch requires minimal swing during the bottom seal, ensuring a perfect fusion of the groove angle. This reduces welding time, is simple to operate, and easily achieves a well-formed root. The weld bead reinforcement on the back of the weld is kept below 1.5mm. This process is easy to master, reduces operational complexity, improves welding quality, and reduces construction costs.

[0057] Obviously, the above embodiments of the present invention are merely examples for the purpose of clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. Those skilled in the art will appreciate that other variations or modifications can be made based on the above description. It is not necessary and impossible to enumerate all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the claims of the present invention.

Claims

1. A thin-walled super duplex stainless steel combined groove welding process, characterized in that: The following steps are involved: S1. Process a groove on the super duplex stainless steel joint to be welded, with a groove angle of 30°±2.5°, a blunt edge height of 0.5-0.8mm, a step length of 0.8-1.5mm, and a circular arc angle of R1-2mm at the junction of the blunt edge and the bevel edge of the groove; S2. Assemble the super duplex stainless steel welded joints with grooves processed thereon; S3, welding is performed using tungsten inert gas arc welding in the form of pulses; S4. Use multi-layer and multi-pass welding.

2. The thin-walled super duplex stainless steel combined groove welding process according to claim 1, characterized in that: In S1, the groove is processed by machining.

3. The thin-walled super duplex stainless steel combined groove welding process according to claim 2, characterized in that: After groove processing, use a stainless steel grinding wheel to clean the weld area and the area 50mm away from the groove to remove debris.

4. The thin-walled super duplex stainless steel combined groove welding process according to claim 1, characterized in that: In S2, the gap between the super duplex stainless steel welded joints with grooves processed is 0 mm.

5. The thin-walled super duplex stainless steel combined groove welding process according to claim 1, characterized in that: In S3, small heat input welding is adopted during the welding process, the welding gun base current is 30-42A, the peak current is 50-72A, the base voltage is 8-10V, the peak voltage is 10-12V, and the welding speed is 2-5cm / min.

6. The thin-walled super duplex stainless steel combined groove welding process according to claim 5, characterized in that: The shielding gas in the welding gun is a high-purity argon-nitrogen mixture, and the shielding gas at the weld root is pure nitrogen.

7. The thin-walled super duplex stainless steel combined groove welding process according to claim 6, characterized in that: When tungsten inert gas welding is performed in the form of pulses, effective discharges occur five times on the discharge gap per unit time.

8. The thin-walled super duplex stainless steel combined groove welding process according to claim 1, characterized in that: In S4, the thickness of each weld layer shall not exceed 2 mm and the interlayer temperature shall not exceed 100°C.

9. The thin-walled super duplex stainless steel combined groove welding process according to claim 8, characterized in that: After each layer of welding is completed, the weld should be cooled immediately with an air gun. The compressed air used in the air gun should be dried in a dryer before use.

10. The thin-walled super duplex stainless steel combined groove welding process according to claim 1, characterized in that: All welding is vertical welding, and the filling cover welding is composed of left and right cross vertical welding.

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