High-strength thin-wall nickel-based alloy steel pipe butt welding process

Abstract

The invention discloses a high-strength thin-wall nickel-based alloy steel pipe butt welding process which comprises the following steps: S1, cleaning the two sides and the back surface of a groove before welding; s2, argon arc welding and electric arc welding are combined, argon arc welding is adopted for bottoming, back face argon protection is conducted during bottoming of argon arc welding, and small swing welding is adopted during bottoming welding; s3, during filling and capping, the input of welding line energy is controlled, small and concentrated welding line energy is adopted, the welding line energy is controlled to be 25 KJ / cm or below, and the interlayer temperature is controlled to be 90-100 DEG C or below; s4, the arc starting points of the interlayer welding beads are staggered by 3-5 mm or above, and the arc craters are filled in the arc stopping process; and S5, after welding is completed, the surface forming condition of the welding seam is checked, nondestructive testing is conducted on the welding seam with the welding seam forming meeting the requirement, and the high-strength thin-wall nickel base alloy steel pipe butt welding technology can better overcome the defects that hot cracks and welding seam air holes are likely to be generated after welding.

Description

Technical Field

[0001] The invention belongs to the technical field of welding, and in particular relates to a high-strength thin-wall nickel-based alloy steel pipe butt welding process. Background Art

[0002] In some polyarylether resin projects, the phenol and methanol medium pipelines of the monomer synthesis unit process pipelines are made of nickel-based alloys. Compared with carbon steel and stainless steel, this material is prone to welding thermal cracks and weld porosity during welding. The main reason for the thermal cracks is its poor weldability, porosity, and high tendency to thermal cracks. During the welding process, most of the impurities in nickel and nickel alloys are insoluble in Ni and form low-melting point eutectics, which are prone to thermal cracks when the weld metal solidifies. In addition, the linear expansion coefficient of nickel-based alloys is close to that of iron, while the thermal conductivity of most nickel-based alloys is much lower than that of iron, resulting in overheating of the heat-affected zone of the fusion welded joint, thereby aggravating the tendency of thermal cracks in the weld metal and the heat-affected zone, causing cracks. Cracks are the most serious defects in welded joints, which are extremely harmful and seriously affect the functionality and safety of finished pipelines. In order to avoid cracks after welding nickel-based alloy steel and defects that are prone to weld porosity, improve the welding process performance of the material, and improve the welding quality, it is necessary to study the welding technology of thin-walled nickel-based alloy pipes as a technical innovation project. Summary of the invention

[0003] To achieve the above object, the technical solution of the present invention is as follows: a high-strength thin-wall nickel-based alloy steel pipe butt welding process, the process comprising the following steps: Step S1, clean both sides and the back of the groove before welding; Step S2, combining argon arc welding with electric arc welding, using argon arc welding for base welding, performing argon gas protection on the back during argon arc welding, and using small swing welding during base welding; Step S3, during filling and capping, control the input of welding line energy, use small and concentrated welding line energy, control the welding line energy below 25KJ / cm, and control the interlayer temperature within 90-100°C; Step S4, the arc starting points of the interlayer welds are staggered by more than 3 to 5 mm, and the arc pit is filled when the arc is closed; Step S5, after welding is completed, the surface forming of the weld is checked, and non-destructive testing is performed on the weld whose forming meets the requirements.

[0004] As an improvement of the present invention, in step S1, before welding, both sides of the groove and the back within 50 mm are cleaned to remove oil stains and surface oxide layer, and chalk powder or anti-fouling agent is applied within 100 mm on both sides of the groove.

[0005] As an improvement of the present invention, the welding joint in step S1 adopts a V-shaped groove with a groove angle of 65±5°, a blunt edge of 0.5-1.5 mm, and a pair gap of 2-3 mm.

[0006] As an improvement of the present invention, in step S3, the wire is appropriately swung when being transported, with the swing amplitude being no greater than 2.5 times the diameter of the welding material, and the wire is swung to both sides of the weld and briefly stopped.

[0007] As an improvement of the present invention, when the tendency of welding thermal cracks is large, the welding materials are cleaned before welding, and the welding rods are baked in place when used; by reducing the welding current, a small and concentrated welding line energy is used, and at the same time, attention is paid to controlling the interlayer temperature at 90-100°C; low-temperature water spray or fireproof cotton wiping is used.

[0008] As an improvement of the present invention, when the tendency of welding thermal cracks is relatively large, a multi-layer and multi-pass welding method is adopted to reduce the weld layer height, and a small swing welding method is adopted as the welding technique to accelerate the flow of liquid metal.

[0009] As an improvement of the present invention, when there is an unfused defect during the welding process, a small swing welding method is adopted during welding; during tungsten inert gas arc welding, the welding gun is 65~80 degrees to the workpiece, and the angle between the welding wire and the workpiece is 15~25 degrees; during manual arc welding, the angle between the welding rod and the base material should be adjusted between 70° and 90°, and different welding positions have different angles.

[0010] As an improvement of the present invention, when there is an unfused defect during welding, it is strictly forbidden to start and extinguish the arc at the groove during welding, the arc starting points of the interlayer welds should be staggered by more than 3 to 5 mm, and the arc pit should be filled when the arc is closed.

[0011] As an improvement of the present invention, step S5 includes performing nondestructive testing on welds whose weld formation meets the requirements, locating defects in welds that fail the nondestructive testing, gently grinding the defective position with a grinder until the defect is polished clean, cleaning the surface of the repair welding position with stainless steel wire, and repairing the weld using an argon arc welding method. The thickness of the weld layer should be thin during repair welding, and the interlayer temperature should be controlled within 100°C. After the repair welding is completed, the weld surface is cleaned and re-tested by non-destructive testing personnel.

[0012] Compared with the prior art, the beneficial effects of the present invention are as follows: the high-strength thin-walled nickel-based alloy steel pipe butt welding process of the present invention can better solve the defects of thermal cracks and weld porosity that are easy to generate after welding; when filling and covering, the input of welding line energy should be controlled, and a small and concentrated welding line energy should be used. The welding line energy is controlled below 25KJ / cm, and the interlayer temperature is controlled within 90-100°C. Prevent the rapid growth of grains in the weld and heat-affected zone. Since nickel-based alloy steel has poor fluidity, it is necessary to swing appropriately when transporting the wire, and the swing amplitude should not be greater than 2.5 times the diameter of the welding material. Swing to both sides of the weld and stay for a while to ensure the formation of the weld; it is strictly forbidden to start and extinguish the arc at the groove during welding to prevent accidental arc crater cracks in the weld. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 This is a flow chart of the nickel-based alloy steel pipe butt welding process steps S1 to S5 in this embodiment; Figure 2 Schematic diagram of the structure of the butt-welded joint of the nickel-based alloy steel pipe in this embodiment. DETAILED DESCRIPTION

[0014] The present invention will be further explained below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the following specific embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention. Example

[0015] In this embodiment, the chemical composition of the nickel-based alloy steel is shown in Table 1, and the physical / mechanical properties are shown in Table 2. The Cr content in the material is usually 15-25%, the Ni content is 30-45%, and contains a small amount of Al, Cu and Ti. Nickel-based alloy steel is a unidirectional austenite structure in the solid state, has poor thermal conductivity, a large linear expansion coefficient, good high and low temperature strength and excellent corrosion resistance. However, it will become brittle when heated in an environment containing S, P or other low melting point metal pollutants.

[0016] Table 1 Chemical composition of N08800 (Incoloy800) nickel-based alloy steel NickelNi Chromium Cr Iron Carbon C Manganese Mn 30.0-35.0 19~23 margin 0.1 1.50 Silicon Phosphorus Sulfur Aluminum AL Copper ≤1.0 ≤0.030 ≤0.015 0.15-0.6 ≤0.75 Table 2 Physical / mechanical properties of N08800 (Incoloy800) nickel-based alloy steel density Melting temperature range Specific heat magnetic 8.0 g / cm3 1393～1427℃ 455J / (kg·℃) none Alloy state Tensile strength RmN / m㎡ Yield strength Rp0.2N / m㎡ Elongation δ5 / % Solution treatment 500 210 ≤35 Temperature ℃ σb / MPa σ0.2 / MPa Elongation δ5 / % 100 425 140 160 300 390 95 115 500 360 80 100 600 300 75 95 Most of the impurities in nickel and nickel alloys are insoluble in Ni during welding. Large welding line energy and interlayer temperature will cause overheating of the weld joint. Ni is easy to form low-melting eutectics with S and P, which will reduce the mechanical properties and corrosion resistance of the weld joint. At the same time, these low-melting eutectics are easy to aggregate on the boundaries of coarse grains. Local liquid film is easy to form in the weld metal and heat-affected zone. Due to the low strength of these eutectics, defects such as thermal cracks and pores are easy to occur under the action of welding stress when the weld metal solidifies. The wall thickness of thin-walled nickel-based alloy steel is too thin, which is not convenient to eliminate and improve crystal transformation by heat treatment process, which is easy to reduce the performance of steel.

[0017] During welding, the welding joint and heat-affected zone must be cleaned, and the protection of the molten pool must be paid attention to. The input of the welding line energy must be stable, small and concentrated to prevent the joint from catalysis, and even produce defects such as pores and cracks. Compared with carbon steel, nickel-based alloy steel has the characteristics of poor thermal conductivity and greater welding viscosity. Therefore, the depth of its welding molten pool is shallow and it is not easy to penetrate. In view of this characteristic, the weld groove adopts a groove form with a large groove angle and a small blunt edge to ensure that the deposited metal solidifies in the appropriate position and ensure the welding quality. At the same time, swing welding is adopted, and a slight pause is made at both ends of the groove to ensure good fusion. Relatively thick pipes (8 mm) can be welded by multi-layer and multi-pass welding.

[0018] The nickel-based alloy steel pipe butt welding process steps of this embodiment include: Bevel grinding and cleaning: Combination Figure 1 and Figure 2 As shown, the groove preparation should be mechanically processed. Before welding, the groove sides and the back within 50mm need to be cleaned to remove oil stains, surface oxide layer, etc. and apply chalk powder or other anti-sticking agent within 100mm on both sides of the break. The welding joint adopts V-shaped groove, groove angle 65±5°, blunt edge 0.5-1.5mm, and assembly gap 2-3mm; Welding process: The welding method is GTAW+SMAW (GTAW is used for wall thickness below 5mm). When argon arc welding is used for base welding, argon gas should be filled on the back for protection. Ensure that the welding operation is carried out under the full protection of argon gas flow to prevent the increase of oxides caused by insufficient gas protection, which will affect the welding quality.

[0019] When welding the base with argon arc, ensure that the back of the root on both sides is well fused. When extinguishing the arc, pay attention to controlling the temperature drop at the arc end to prevent shrinkage holes and arc crater cracks. When welding the base, use small swing welding to blow the oxides on the surface of the molten pool to the edge of the weld to improve the cleanliness of the molten pool and enhance the fusion of the root weld.

[0020] When filling and covering, the input of welding line energy should be controlled, and a small and concentrated welding line energy should be used. The welding line energy should be controlled below 25KJ / cm, and the interlayer temperature should be controlled within 90-100℃. Prevent the rapid growth of grains in the weld and heat-affected zone. Since nickel-based alloy steel has poor fluidity, it is necessary to swing the wire appropriately during transportation, and the swing amplitude should not exceed 2.5 times the diameter of the welding material. Swing to both sides of the weld and stay for a while to ensure the formation of the weld. After each layer of welding, check the weld. If necessary, use a grinding wheel or stainless steel wire wheel to clean the oxides and residues on the weld surface to ensure the cleanliness of the weld.

[0021] It is strictly forbidden to start and extinguish the arc at the groove during welding to prevent accidental arc crater cracks in the weld. The arc starting points of the interlayer weld should be staggered by more than 3 to 5 mm. The arc crater must be filled when the arc is closed.

[0022] Table 3 Welding process parameters Welding level Welding material model Diameter (mm) Welding current / A Welding voltage / V Welding speed cm / min Line energy KJ / cm Protective air flow L / min Primer GTAW ERNiCr-3 2.4 Straightforward 100-110 11-12 6-7 ≤11.3 20-25 Filling SMAW ENi6133 3.2 Straight-reverse 100-105 23-25 12-13 ≤12.1 / Cover SMAW ENi6133 3.2 Straight back 100-110 23-25 14-15 ≤11 / After welding is completed, check the surface forming of the weld. A qualified weld should be a convex weld without undercut. Perform nondestructive testing on welds that meet the requirements. For welds that fail the nondestructive testing, locate the defects according to the notice issued by the nondestructive testing personnel, and use a grinder to gently grind the defective position until the defect is polished clean. Use stainless steel wire to clean the surface of the repair welding position, and use argon arc welding to repair the welding. The thickness of the weld layer should be thin during repair welding, and the interlayer temperature should be controlled within 100°C. After the repair welding is completed, the weld surface is cleaned and re-tested by the nondestructive testing personnel.

[0023] In this embodiment, when the tendency of welding hot cracks is large, Ni is easy to form a low melting point eutectic with S and P during welding, which will reduce the mechanical properties and corrosion resistance of the welded joint. When the weld metal solidifies, it is easy to produce defects such as hot cracks and pores under the action of welding stress. Take the following steps: 1) Clean the welding materials before welding to ensure cleanliness. When using welding rods, the welding rods must be baked properly; 2) Control the input of welding line energy by reducing welding current and speeding up welding speed, use small and concentrated welding line energy, and pay attention to controlling the interlayer temperature at 90-100℃; 3) Use low-temperature water spray or fire-proof cotton to wipe low-temperature water to achieve rapid cooling of the weld temperature, reduce temperature concentration and high-temperature residence time, and reduce the occurrence of thermal cracks.

[0024] 4) Use multi-layer and multi-pass welding to reduce the weld layer height and speed up the cooling of liquid metal. The welding technique uses a small swing welding method to speed up the flow of liquid metal, ensure that the gas escapes completely before solidification, and reduce the generation of pores.

[0025] In this embodiment, when the defect of unfusion occurs, the fluidity of the deposited metal is poor, and the poor fusion of the liquid metal easily leads to defects such as unfusion and undercut. The alloy has poor thermal conductivity, and if the arc is not closed properly, shrinkage cavities and unmelted parts will occur. Take the following steps: 1) When welding, use a small swing welding method to speed up the flow of liquid metal and ensure the fusion of liquid metal; when welding with tungsten inert gas arc welding, the welding gun should be 65~80 degrees to the workpiece, and the angle between the welding wire and the workpiece should be 15~25 degrees. When welding manually, the angle between the electrode and the parent material should be adjusted between 70° and 90°, and different welding positions have different angles. The smaller the angle, the thinner the weld. The specific angle is subject to the welder's welding proficiency. The purpose is to protect the weld from forming well.

[0026] 2) It is strictly forbidden to start and extinguish the arc at the groove during welding to prevent accidental arc crater cracks in the weld. The arc starting points of the interlayer weld should be staggered by more than 3 to 5 mm. The arc crater must be filled when the arc is closed.

[0027] In the polyarylether resin project test, the high-strength thin-walled nickel-based alloy steel pipe butt welding process in this embodiment has 100% qualified weld surface quality inspection, 98.9% qualified rate of RT inspection (586 films), and the main unqualified defects are pores and unfused. The on-site pressure is qualified. The pipeline system has been running stably for half a year, fully meeting the use requirements, and no leakage points have been found. The successful trial of this project fully demonstrates the feasibility of the N08800 (Incoloy800) high-strength thin-walled nickel-based alloy steel pipe butt welding process. The research and development of this technology has accumulated valuable construction experience for similar projects in the future for our company.

[0028] It should be noted that the above content only illustrates the technical idea of ​​the present invention and cannot be used to limit the protection scope of the present invention. For ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications all fall within the protection scope of the claims of the present invention.

Claims

1. A high-strength thin-walled nickel-based alloy steel pipe butt welding process, characterized in that: The process comprises the following steps, Step S1, clean both sides and the back of the groove before welding; Step S2, combining argon arc welding with electric arc welding, using argon arc welding for base welding, performing argon gas protection on the back during argon arc welding, and using small swing welding during base welding; Step S3, during filling and capping, control the input of welding line energy, use small and concentrated welding line energy, control the welding line energy below 25KJ / cm, and control the interlayer temperature within 90-100°C; Step S4, the arc starting points of the interlayer welds are staggered by more than 3 to 5 mm, and the arc pit is filled when the arc is closed; Step S5, after welding is completed, the surface forming of the weld is checked, and non-destructive testing is performed on the weld whose forming meets the requirements.

2. The high-strength thin-walled nickel-based alloy steel pipe butt welding process according to claim 1 is characterized in that: In the step S1, before welding, both sides of the groove and the back within 50 mm need to be cleaned to remove oil stains and surface oxide layer, and chalk powder or anti-fouling agent is applied within 100 mm on both sides of the groove.

3. The high-strength thin-walled nickel-based alloy steel pipe butt welding process according to claim 1 is characterized in that: In the step S1, the welding joint adopts a V-shaped groove with a groove angle of 65±5°, a blunt edge of 0.5-1.5 mm, and a pair gap of 2-3 mm.

4. The high-strength thin-walled nickel-based alloy steel pipe butt welding process according to claim 1 is characterized in that: In step S3, the wire is swung appropriately when being transported, with the swing amplitude not exceeding 2.5 times of the diameter of the welding material, and the wire is swung to both sides of the weld and stopped for a while.

5. The high-strength thin-walled nickel-based alloy steel pipe butt welding process according to claim 1 is characterized in that: When the tendency of welding thermal cracks is large, the welding materials should be cleaned before welding, and the welding rods should be baked in place when used; by reducing the welding current, using a small and concentrated welding line energy, and paying attention to controlling the interlayer temperature at 90-100℃; use low-temperature water spray or fireproof cotton to wipe the low-temperature water.

6. The high-strength thin-walled nickel-based alloy steel pipe butt welding process according to claim 1 is characterized in that: When the tendency of welding thermal cracks is large, multi-layer and multi-pass welding is adopted to reduce the height of the weld layer, and the welding technique adopts a small swing welding method to speed up the flow of liquid metal.

7. The high-strength thin-walled nickel-based alloy steel pipe butt welding process according to claim 1 is characterized in that: When there is a lack of fusion defect during the welding process, a small swing welding method is used during welding; during tungsten inert gas welding, the welding gun is 65~80 degrees to the workpiece, and the angle between the welding wire and the workpiece is 15~25 degrees; during manual arc welding, the angle between the electrode and the base material should be adjusted between 70° and 90°, and different welding positions have different angles.

8. The high-strength thin-walled nickel-based alloy steel pipe butt welding process according to claim 7 is characterized in that: When there is an unfused defect during the welding process, it is strictly forbidden to start and extinguish the arc at the groove during welding. The arc starting points of the interlayer welds should be staggered by more than 3 to 5 mm, and the arc pit should be filled when the arc is closed.

9. The high-strength thin-walled nickel-based alloy steel pipe butt welding process according to claim 1 is characterized in that: The step S5 includes performing nondestructive testing on welds that meet the requirements, and locating defects on welds that fail the nondestructive testing, gently grinding the defective position with a grinder until the defect is ground clean, cleaning the surface of the repair welding position with a stainless steel wire, and repairing the weld using an argon arc welding method. The thickness of the weld layer should be thin during repair welding, and the interlayer temperature should be controlled within 100° C. After the repair welding is completed, the weld surface is cleaned and re-tested by the nondestructive testing personnel.

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