Welding method of low alloy high strength steel pipeline and stainless steel bellows

Abstract

The present invention provides a method for welding a low-alloy high-strength steel pipe to a stainless steel bellows. The method comprises: forming a single-sided groove on the end of the low-alloy high-strength steel pipe to be welded; welding a weld bead of a preset thickness at the blunt edge and melting the blunt edge; surfacing a weld of a preset weld length at each predetermined weld distance at the end of the stainless steel bellows; welding the surface weld using a segmented welding method, applying high-pressure cooling to the stainless steel bellows side and low-pressure micro-cooling to the stainless steel bellows side. The present invention prevents the stainless steel side from overheating and causing chromium molecules to rapidly migrate to the low-alloy high-strength steel side, preventing chromium carbide from forming on the stainless steel bellows side. This ensures that the chromium content on the bellows surface is greater than 12%, prevents the formation of chromium-depleted areas and thus intergranular corrosion, and prevents excessive temperature and C migration on the Q345B side, thereby ensuring welding quality.

Description

Technical Field

[0001] The present invention relates to the field of maintenance metallurgy technology, and in particular to a method for welding a low-alloy high-strength steel pipeline and a stainless steel bellows. Background Art

[0002] At present, in a certain project, there are 400mm*0.5mm diameter SUS304 stainless steel and 450mm*20mm diameter Q345B low alloy high strength steel pipes between the blast furnace body shell and the steel structure column at a distance of 800mm. The SUS304 stainless steel and 450mm*20mm diameter Q345B low alloy high strength steel pipes need to be welded.

[0003] However, when welding SUS304 stainless steel and 450mm*20mm diameter Q345B low-alloy high-strength steel pipes, the current is small, the welding pool temperature of the low-alloy high-strength steel pipe is low, and welding is impossible; the current is large, and the stainless steel bellows melts into a hole during welding, causing the entire bellows to be scrapped; at the same time, the pipeline medium is coal gas, which contains chloride ions, which are very easy to corrode the weld. Stainless steel is prone to intergranular corrosion, and chloride ions penetrate into the lattice, causing the weld to crack. Summary of the Invention

[0004] In view of this, the present invention proposes a method for welding low-alloy high-strength steel pipes and stainless steel bellows, which aims to solve the problem that the welding current of existing low-alloy high-strength steel pipes and ultra-thin stainless steel bellows is large, causing the stainless steel bellows to melt into a hole during welding, resulting in the entire bellows being scrapped.

[0005] The present invention proposes a method for welding a low-alloy high-strength steel pipeline and a stainless steel bellows, which comprises the following steps: processing the end portion of the low-alloy high-strength steel pipeline to be welded to form a single-sided groove, grinding the single-sided groove angle to a preset angle, and the blunt edge to a preset length; welding a weld bead of preset thickness at the blunt edge of the single-sided groove of the low-alloy high-strength steel pipeline, and melting the blunt edge; using a surfacing method to weld the end portion of the stainless steel bellows to be welded, and surfacing a weld with a preset weld length at each preset weld spacing; grinding the groove surface flat, and leaving a gap of preset gap width between the stainless steel bellows and the low-alloy high-strength steel pipeline for assembly; using an intermittent welding method to weld the surface weld, and during welding, high-pressure cooling is applied to the stainless steel bellows side while welding, and low-pressure micro-cooling is applied to the stainless steel bellows side at the same time.

[0006] Furthermore, in the above-mentioned method for welding a low-alloy high-strength steel pipe to a stainless steel bellows, when welding a weld of a preset thickness at the blunt edge of a single-sided groove of the low-alloy high-strength steel pipe, the current is 80A to 100A, the welding speed is 180mm / min to 350mm / min, the gas flow rate is 5ml to 8ml, and a continuous wire feeding welding method is adopted. During welding, the arc is lifted toward the upper part of the groove.

[0007] Furthermore, in the above-mentioned method for welding low-alloy high-strength steel pipes and stainless steel bellows, a surfacing method is adopted at the end portion to be welded of the stainless steel bellows. When surfacing the weld of a preset weld length at each preset weld spacing, the current is 50A to 70A, the welding speed is 150mm / min to 300mm / min, the gas flow rate is 4ml to 6ml, and an intermittent wire feeding spot welding method is adopted. The wire is fed at one-third of the white flame in the middle of the arc, and a backward dragging action is required during spot welding.

[0008] Furthermore, in the above-mentioned method for welding low-alloy high-strength steel pipes and stainless steel bellows, when the surface welds are welded by the intermittent welding method, the welding length each time is 50 mm, the interval is 150 mm, the current is 70 A to 90 A, the welding speed is 160 mm / min to 320 mm / min, and the gas flow rate is 5 ml to 8 ml. When 0.5 mm molten holes are seen formed on both sides of the groove, the wire is fed to one-third of the white flame in the middle of the arc, and the welding gun is moved forward evenly. When welding a 150 mm weld, the arc is struck at the Q345B side groove about 10 mm in front of the original weld. The original weld forms a molten pool and then the wire is fed for welding. The welding speed is matched with the wire feeding frequency, so that the weld color becomes golden yellow.

[0009] Furthermore, in the above-mentioned method of welding a low-alloy high-strength steel pipe to a stainless steel bellows, when welding a weld of preset thickness at the blunt edge of the single-sided groove of the low-alloy high-strength steel pipe, the sharpness of the tungsten electrode used is sharper than that used when welding the end portion to be welded of the stainless steel bellows.

[0010] Furthermore, in the above-mentioned method of welding low-alloy high-strength steel pipes and stainless steel bellows, the preset angle is 50°, the preset length is 5 mm, the preset thickness is 1 mm, the preset weld spacing is 15 mm, the preset weld length is 5 mm, and the preset gap width is 1 mm.

[0011] Furthermore, in the above-mentioned welding method of low-alloy high-strength steel pipeline and stainless steel bellows, high-purity argon is used as the shielding gas when high-pressure cooling is adopted on the stainless steel bellows side and low-pressure micro-cooling is adopted on the stainless steel bellows side.

[0012] Furthermore, the above-mentioned method for welding the low-alloy high-strength steel pipeline and the stainless steel bellows adopts an argon arc welding gun for welding.

[0013] Furthermore, in the above-mentioned method for welding a low-alloy high-strength steel pipeline to a stainless steel corrugated pipe, when the surface weld is welded by the intermittent welding method, the welding wire used is a stainless steel argon arc welding wire.

[0014] Furthermore, in the above-mentioned method for welding the low-alloy high-strength steel pipeline and the stainless steel bellows, a low current, fast welding, and two-layer three-pass welding method is used for welding.

[0015] The present invention provides a method for welding a low-alloy high-strength steel pipe and a stainless steel bellows, which comprises welding a weld bead of a preset thickness at the blunt edge of a single-sided groove of the low-alloy high-strength steel pipe, melting the blunt edge, and adopting a surfacing welding method at the end portion to be welded of the stainless steel bellows, surfacing a weld with a preset weld length at each preset weld spacing; grinding and smoothing the groove surface, and leaving a gap of a preset gap width between the stainless steel bellows and the low-alloy high-strength steel pipe for assembly; finally, adopting an intermittent welding method to weld the surface weld, and during welding, the side of the stainless steel bellows is welded while welding. Use high pressure cooling, and at the same time use low pressure micro-cooling on the stainless steel bellows side, so as to avoid the stainless steel side from overheating and forming Cr molecules to move rapidly to the low alloy high strength steel pipe side, and also prevent the stainless steel bellows side from forming chromium carbide in time, ensuring that the Cr on the bellows surface is greater than 12%, no chromium-poor area will be formed, and thus no intergranular corrosion will be formed, and the temperature of the Q345B side will not be too high and C migration will occur, thus ensuring the welding quality, and solving the problem that the existing low alloy high strength steel pipeline and ultra-thin stainless steel bellows welding current is large, causing the stainless steel bellows to melt into a hole during welding, resulting in the entire bellows being scrapped. At the same time, this method also solves the welding problems of narrow welding positions, pipes of different thicknesses, and pipes of different materials. The operation is simple and convenient, the stainless steel side prevents Cr from moving rapidly, uses high-purity argon for cooling, and prevents the rapid migration of C elements in Q345B steel. By selecting ultra-low carbon stainless steel welding wire, the metallographic structure of the stainless steel side weld will not become martensite, which will cause the weld to crack. This method can solve the problem of welding dissimilar metals in a narrow space without replacing the low-alloy high-strength steel pipeline, and achieve the goals of high efficiency, economy and labor saving. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiment below. The accompanying drawings are for illustration purposes only and are not to be considered as limiting the present invention. The same reference symbols are used throughout the drawings to represent the same components. In the drawings:

[0017] Figure 1This is a flow chart of a method for welding a low-alloy high-strength steel pipeline to a stainless steel bellows provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0018] The exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although exemplary embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the present disclosure to those skilled in the art. It should be noted that, unless there is a conflict, the embodiments of the present disclosure and the features described in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0019] See also Figure 1 , which is a flowchart of a method for welding a low-alloy high-strength steel pipe to a stainless steel bellows provided by an embodiment of the present invention. As shown in the figure, the method for welding a low-alloy high-strength steel pipe to a stainless steel bellows includes the following steps:

[0020] Step S1: Processing the end portion of a low-alloy high-strength steel pipe to be welded to form a single-sided groove, wherein the angle of the single-sided groove is ground to a preset angle, and the blunt edge is a preset length.

[0021] Specifically, the preset angle is 50° and the preset length is 5 mm, that is, the single-side groove of the low-alloy high-strength steel is ground to 50° and the blunt edge is 0.5 mm.

[0022] Step S2: welding a weld bead of a preset thickness at the blunt edge of the single-side groove of the low-alloy high-strength steel pipeline, and melting the blunt edge.

[0023] Specifically, the preset thickness is 1mm. This means that a weld bead approximately 1mm thick is welded on the 0.5mm blunt edge of a single-sided groove of low-alloy high-strength steel, simultaneously melting the blunt edge. Furthermore, when welding a weld bead of the preset thickness on the blunt edge of a single-sided groove of a low-alloy high-strength steel pipeline, the current is 80A to 100A, the welding speed is 180mm / min to 350mm / min, and the gas flow rate is 5ml to 8ml. Continuous wire feeding is used. The arc is lifted upwards during welding, facilitating a smooth transition between the weld and the low-alloy high-strength steel groove. Furthermore, the tungsten electrode for welding low-alloy high-strength steel is ground slightly to a sharper point to facilitate arc temperature concentration.

[0024] Step S3: surfacing welding is performed on the end portion of the stainless steel corrugated pipe to be welded, with a preset weld length being surfacing welded at intervals of a preset weld spacing.

[0025] Specifically, the preset weld spacing is 15mm, and the preset weld length is 5mm. That is, for US304 stainless steel bellows, a 5mm weld is deposited every 15mm. When welding stainless steel bellows, the tungsten electrode should not be sharpened too much to facilitate the expansion of the arc range. The current is I = 50A to 70A, the welding speed is V = 150mm / min to 300mm / min, and the gas flow rate is 4ml to 6ml. Intermittent wire feeding spot welding is used, with the wire fed at one-third of the white flame in the middle of the arc. During spot welding, a backward dragging motion is required to help the new molten pool overlap the old molten pool a little more and avoid burning through the groove edge of the bellows.

[0026] Step S4: Grind the groove surface to make it smooth, and leave a gap of a preset gap width between the stainless steel bellows and the low-alloy high-strength steel pipe for assembly.

[0027] Specifically, the preset gap width is 1mm. After a week of welding, the weld is guaranteed to be defect-free. The groove surface is then ground smooth, leaving a 1mm gap between the US304 stainless steel bellows and the Q345B low-alloy high-strength steel pipe for assembly. Surface welds are welded using intermittent welding, with each weld length of 50mm and intervals of 150mm. The current is 70A to 90A, the welding speed is 160mm / min to 320mm / min, and the gas flow rate is 5ml to 8ml. When a 0.5mm melt hole is formed on either side of the groove, the wire is fed to the arc, one-third of the way along the white flame, and the welding torch is moved forward evenly. When welding a 150mm weld, the arc is struck at the Q345B side groove approximately 10mm in front of the original weld. The wire is then fed after a molten pool forms on the original weld. The welding speed is coordinated with the wire feeding frequency, resulting in a golden-yellow weld color.

[0028] Step S5, using the intermittent welding method to weld the surface weld, and during welding, high pressure cooling is applied to the stainless steel bellows side while welding, and low pressure micro cooling is applied to the stainless steel bellows side at the same time.

[0029] Specifically, the welding is completed by welding 50mm long each time with a small current and retaining a 150mm long interval welding method. While welding, the stainless steel bellows side is cooled with high-purity argon gas at high pressure (flow rate 15ml), and the Q345B side is slightly cooled with high-purity argon gas at low pressure (flow rate 5ml). This prevents the stainless steel side from overheating and forming Cr molecules that quickly move to the low-alloy high-strength steel pipe side, and also prevents the stainless steel bellows side from forming chromium carbide in time, ensuring that the Cr content on the bellows surface is greater than 12%, and no chromium-poor area will be formed, thus no intergranular corrosion will be formed, and the temperature on the Q345B side will not be too high and C will not migrate, thus ensuring the welding quality. The weld is inspected to verify whether it meets the preset conditions, which include: uniform weld width, smooth transition between the weld and the base material, golden or silver-white weld surface color, and dye flaw detection inspection of the weld surface without defects such as pores and undercuts.

[0030] In this embodiment, in order to achieve welding in a small welding space, preferably, an argon arc welding gun is selected, which is small and easy to operate; and a welder with good skills, a height of less than 1.6 meters, and a weight of 55-60 kilograms is selected.

[0031] In this embodiment, the stainless steel weld is diluted by the low-alloy, high-strength alloying elements to form a martensitic structure, making the weld structure brittle and hard, and very easy to crack. To avoid the occurrence of weld cracks, it is preferably used to spot weld or gap weld (welding 5mm at intervals of 15mm) so that the heat of the weld is not easily concentrated and the heat is easily dissipated.

[0032] In this embodiment, the linear expansion coefficients of US304 stainless steel and Q345B low-alloy high-strength steel are different (the coefficient ratio is 14:17), which makes the interface between the weld and the base material (fusion line) prone to cracking. To avoid cracking, welding materials with relatively similar properties of the two steels are selected, welding materials with good plasticity are selected, and the weld metal structure stability is selected to be compatible with the two base materials. Based on the above requirements, ER309L*Φ0.8 stainless steel argon arc welding wire with ultra-low carbon, slightly higher nickel-chromium content, and good toughness is selected. High-purity argon (99.999%) is selected as the shielding gas. During welding, a low welding current, fast welding, and two-layer three-pass welding method are selected.

[0033] In summary, the welding method of low-alloy high-strength steel pipe and stainless steel bellows provided in this embodiment is to weld a weld of preset thickness at the blunt edge of the single-sided groove of the low-alloy high-strength steel pipe, melt the blunt edge, and adopt a surfacing method at the end to be welded of the stainless steel bellows, and surfacing a weld of preset weld length at each preset weld spacing; the groove surface is polished and smoothed, and a gap of preset gap width is left between the stainless steel bellows and the low-alloy high-strength steel pipe for assembly; finally, the surface weld is welded by the segment welding method, and the stainless steel bellows is welded while welding. High-pressure cooling is adopted on the side, while low-pressure micro-cooling is adopted on the side of the stainless steel bellows. This prevents the stainless steel side from overheating and forming Cr molecules that move rapidly to the low-alloy high-strength steel pipe side, and also prevents the stainless steel bellows side from forming chromium carbide in time, ensuring that the Cr on the surface of the bellows is greater than 12%, and no chromium-poor area will be formed, which will not form intergranular corrosion, and will not cause the temperature of the Q345B side to be too high and C migration, thus ensuring the welding quality and solving the problem that the existing low-alloy high-strength steel pipeline and ultra-thin stainless steel bellows welding current is large, causing the stainless steel bellows to melt into a hole during welding, resulting in the entire bellows being scrapped. At the same time, this method also solves the welding problems of narrow welding positions, pipes of different thicknesses, and pipes of different materials. The operation is simple and convenient. The stainless steel side prevents Cr from moving rapidly and uses high-purity argon for cooling. At the same time, it prevents the rapid migration of C elements in Q345B steel and selects ultra-low carbon stainless steel welding wire. The metallographic structure of the weld on the stainless steel side will not become martensite, which will cause the weld to crack. This method can solve the problem of welding dissimilar metals in a narrow space without replacing the low-alloy high-strength steel pipeline, and achieve the goals of high efficiency, economy and labor saving.

[0034] It should be noted that, in the description of the present invention, terms such as "up", "down", "left", "right", "inside", and "outside" indicating directions or positional relationships are based on the directions or positional relationships shown in the accompanying drawings. This is only for the convenience of description and does not indicate or imply that the device or element must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it cannot be understood as a limitation on the present invention.

[0035] Furthermore, it should be noted that, in the description of the present invention, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "connected" should be understood broadly. For example, they may refer to fixed connections, detachable connections, or integral connections; they may refer to direct connections, indirect connections through an intermediary, or internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0036] Obviously, those skilled in the art may make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if such changes and modifications fall within the scope of the claims and their equivalents, the present invention is intended to include such changes and modifications.

Claims

1. A method for welding a low alloy high strength steel pipeline to a stainless steel bellows, characterized in that: The steps include: The end of the low-alloy high-strength steel pipe to be welded is processed to form a single-sided groove, the angle of the single-sided groove is ground to a preset angle, and the blunt edge is a preset length; Weld a weld bead of preset thickness on the blunt edge of the single-side groove of the low-alloy high-strength steel pipeline and melt the blunt edge; At the end of the stainless steel corrugated pipe to be welded, a surfacing method is adopted, and a weld with a preset weld length is surfacing at each preset weld interval; The groove surface is ground and smoothed, and a gap of preset width is left between the stainless steel bellows and the low-alloy high-strength steel pipe for assembly; The surface welds are welded by the intermittent welding method, and during welding, high pressure cooling is applied to the stainless steel bellows side while welding, and low pressure micro cooling is applied to the stainless steel bellows side at the same time; When welding a weld of a preset thickness at the blunt edge of a single-sided groove of a low-alloy high-strength steel pipeline, the current is 80A to 100A, the welding speed is 180mm / min to 350mm / min, and a continuous wire feeding welding method is used. During welding, the arc is lifted toward the upper part of the groove; At the end portion to be welded of the stainless steel corrugated pipe, a surfacing welding method is adopted. At each preset weld spacing, a preset weld length weld is surfacing once. The current is 50A to 70A, the welding speed is 150mm / min to 300mm / min, and an intermittent wire feeding spot welding method is adopted. The wire is fed at one-third of the white flame in the middle of the arc. A backward dragging action is required during spot welding. When the intermittent welding method is used to weld the surface weld, the welding length each time is 50 mm, the interval is 150 mm, the current is 70A to 90A, and the welding speed is 160 mm / min to 320 mm / min. When 0.5 mm molten holes are seen on both sides of the groove, the wire is fed to one-third of the white flame in the middle of the arc, and the welding gun is moved forward evenly. When welding a 150 mm weld, the arc is struck at the Q345B side groove about 10 mm in front of the original weld. The original weld forms a molten pool and then the wire is fed for welding. The welding speed is matched with the wire feeding frequency, so that the weld color becomes golden yellow.

2. The method for welding a low alloy high strength steel pipeline to a stainless steel bellows according to claim 1, characterized in that: When welding a weld of preset thickness at the blunt edge of the single-side groove of the low-alloy high-strength steel pipeline, the tungsten electrode used is sharper than the tungsten electrode used for welding the end portion to be welded of the stainless steel bellows.

3. The method for welding a low alloy high strength steel pipeline to a stainless steel bellows according to claim 1, characterized in that: The preset angle is 50°, the preset length is 5 mm, the preset thickness is 1 mm, the preset weld spacing is 15 mm, the preset weld length is 5 mm, and the preset gap width is 1 mm.

4. The method for welding a low alloy high strength steel pipeline to a stainless steel bellows according to claim 1, characterized in that: When high-pressure cooling is adopted on the stainless steel bellows side and low-pressure micro-cooling is adopted on the stainless steel bellows side, high-purity argon is used as the protective gas.

5. The method for welding a low alloy high strength steel pipeline to a stainless steel bellows according to claim 1, characterized in that: Welding is performed using a argon arc welding gun.

6. The method for welding a low alloy high strength steel pipeline to a stainless steel bellows according to claim 1, characterized in that: When the surface weld is welded by the intermittent welding method, the welding wire used is a stainless steel argon arc welding wire.

7. The method for welding a low alloy high strength steel pipeline to a stainless steel bellows according to claim 1, characterized in that: During welding, a low current, fast welding, and two-layer three-pass welding method is used.

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