A method for welding a stainless steel pipe by argon arc welding from the back side without argon protection

Abstract

The present application relates to the technical field of stainless steel pipeline welding, and particularly relates to a method for argon arc welding of a back surface of a fixed welding opening of a stainless steel pipeline without argon protection. A groove is machined; a gasket is made; a first end of a stainless steel pipe is heated, one end of the gasket is inserted into the first stainless steel pipe from the end, and the temperature is lowered; argon arc welding is performed without welding wire, the gasket and the first stainless steel pipe are fully welded together in the medium flow direction by self-melting of the first stainless steel pipe and the gasket, and the welding height is less than or equal to the thickness of the gasket; the groove of the first stainless steel pipe is fully welded around by argon arc welding; a second end of a second stainless steel pipe is heated, the other end of the gasket is inserted into the second stainless steel pipe, and the temperature is lowered; backing welding is performed on the inner side, and filling welding is performed on the outer side. The backing welding by argon arc welding can well protect the back surface by argon protection, so that oxidation and carburization of the welding meat are avoided, the welding efficiency is high, and the method is suitable for small pipe diameters.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of stainless steel pipeline welding, in particular to a method for argon arc welding of a fixed weld of a stainless steel pipeline without argon protection on the back. BACKGROUND

[0002] Austenitic stainless steel pipeline has good corrosion resistance, high temperature resistance, low temperature resistance and other properties, so in metallurgical, petrochemical and other engineering construction, more and more liquid, gaseous (such as oxygen, nitrogen, argon, hydraulic oil, lubricating oil, ammonia, styrene, ethylene, etc.) medium process pipeline requires the use of austenitic stainless steel pipeline. Common austenitic stainless steel pipeline materials include 304, 316, 316L, etc.

[0003] When the weld of the stainless steel pipeline is argon arc welding, the front of the weld is protected by argon gas sprayed from the welding gun, and the back of the weld is oxidized and carburized due to contact with oxygen in the air at high temperature, which loses the corrosion resistance, high temperature resistance and low temperature resistance of stainless steel. Therefore, before welding the stainless steel pipeline, argon protection is required inside the pipeline. For rotating welds, sponges can be used to block the inside of the stainless steel pipeline and the two sides of the weld during pipeline prefabrication, or special argon filling tools that are easy to move and transport can be used for argon protection inside the stainless steel pipeline, or water-soluble paper can be used to block the two sides of the weld inside the stainless steel pipeline for argon protection. The water-soluble paper can be dissolved and washed away during water pressure test. During pipeline prefabrication, the above methods can effectively ensure the quality of the weld and prevent internal oxidation of the weld.

[0004] However, during pipeline installation, especially when encountering fixed welds, especially during stainless steel pipeline maintenance and replacement operations, the existing welding methods have the following defects: long distance stainless steel pipeline, argon arc welding during maintenance operations, but the back cannot be well protected by argon, and the back of the weld is prone to oxidation and carburization; 2, low welding efficiency; 3, not suitable for small diameter stainless steel pipelines. SUMMARY

[0005] In order to overcome the shortcomings of the prior art, the present application provides a method for argon arc welding of a fixed weld of a stainless steel pipeline without argon protection on the back. The back of the weld can be well protected by argon during argon arc welding, which avoids oxidation and carburization of the weld, has high welding efficiency, and is suitable for small diameters.

[0006] In order to achieve the above purpose, the present application adopts the following technical scheme:

[0007] A method for argon arc welding of a fixed weld of a stainless steel pipeline without argon protection on the back, specifically comprising the following steps:

[0008] 1) Machining a bevel on the end of the first stainless steel pipe and the end of the second stainless steel pipe to be welded;

[0009] 2) make a gasket, the gasket material is the same as the first stainless steel pipe, the second stainless steel pipe, the gasket is tubular, its outer diameter is equal to the inner diameter of the first stainless steel pipe and the second stainless steel pipe;

[0010] 3) heat the end of the first stainless steel pipe, insert one end of the gasket into the first stainless steel pipe from the end, and after cooling, the gasket is in close contact with the inner wall of the first stainless steel pipe without gaps;

[0011] 4) without welding wire, the gasket and the first stainless steel pipe are fully welded together in the direction of medium flow by self-melting of the first stainless steel pipe and the gasket, and the weld height is less than or equal to the thickness of the gasket;

[0012] 5) use argon arc welding to weld the bevel of the first stainless steel pipe for one turn;

[0013] 6) heat the end of the second stainless steel pipe, insert the other end of the gasket into the second stainless steel pipe, and after cooling, the gasket is in close contact with the inner wall of the second stainless steel pipe without gaps;

[0014] 7) perform backing welding on the inside of the bevel of the first stainless steel pipe and the second stainless steel pipe, and perform filling welding on the outside.

[0015] Further, the bevel in step 1) is 20-40°, with a blunt edge, and the inner chamfer is 30-50°.

[0016] Preferably, the stainless steel pipe is ground with a single 30° bevel using an angle grinder, leaving a 1mm blunt edge and a 45° inner chamfer.

[0017] Further, step 2) also includes cleaning the oil stains on the ends of the first stainless steel pipe and the second stainless steel pipe and the gasket using alcohol or acetone solution.

[0018] Further, the thickness of the gasket in step 2) is 3-4mm.

[0019] Further, in steps 3) and 6), the heating temperature is lower than 100℃, and a gas welding gun is used to heat at a distance of 100±20mm from the bevel.

[0020] Further, the argon arc welding current in step 5) is 90-100A.

[0021] Further, the gap between the bevel of the first stainless steel pipe and the bevel of the first stainless steel pipe in step 6) is 3-4mm.

[0022] Further, the welding current in step 7) is 90-100A; if the thickness of the first stainless steel pipe and the second stainless steel pipe is greater than 5mm, the filling welding is multi-layered.

[0023] Further, the welding wire used for welding is the same material as the first stainless steel pipe and the second stainless steel pipe.

[0024] The beneficial effects of the present application compared with the prior art are:

[0025] 1、The present application adopts the principle of thermal expansion and cold contraction to make the gasket and the inner wall of the stainless steel pipe tightly contact without gap, and isolates the molten pool from air during the assembly and welding of the stainless steel fixed weld, thereby avoiding oxidation and carburization of the weld, solving the problem of argon arc welding backing encountered in long distance stainless steel pipeline and stainless steel pipeline maintenance operation, preventing oxidation and carburization of the back of the weld, improving the welding efficiency, and easily achieving the requirements of specifications and design documents.

[0026] The gasket and the first stainless steel pipe are fully welded together in the medium flow direction by argon arc welding without welding wire, and the welding process does not require welding wire, only the argon arc welding gun is inserted into the pipe for operation, and the pipe is self-melted, which can be operated on small diameter stainless steel pipes; the prior art requires welding wire, and cannot be operated on small diameter pipes.

[0027] The first stainless steel pipe and the second stainless steel pipe are butt welded at the inner side of the bevel, and the outer side is filled with welding, which is covered with an arc, fast and efficient. The prior art is full argon arc welding, which is low in efficiency.

[0028] 2、Compared with the prior art, the gasket end and the stainless steel pipe are fully welded together in the medium flow direction, which has the advantages that only one side of the gasket end is connected with the stainless steel pipe, and the welding side is the direction of medium inflow, and the non-welding side is the direction of outflow, which avoids the accumulation of impurities during flushing and purging, and affects the cleanliness of the pipeline.

[0029] 3、The present application gives the welding current range value in multiple places, which is to prevent the gasket and the pipe material from being melted and oxidized and carburized due to excessive current, thereby affecting the quality of the weld nondestructive testing.

[0030] 4、The bevel of the present application is 20-40°, leaving a blunt edge, and the inward chamfer is 30-50°. Compared with the prior art, the inner bevel has the advantages that the gasket outer wall and the stainless steel pipe inner wall are tightly contacted after welding without gap, the root penetration is facilitated, and the local incomplete penetration defect at the root is prevented. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 is a schematic diagram of the welding of the first stainless steel pipe and the gasket of the present application;

[0032] Figure 2 is a schematic diagram of the assembly and welding of the first stainless steel pipe and the second stainless steel pipe of the present application.

[0033] In the figure: 1 - gasket and first stainless steel tube full welding 2 - gasket outer wall and first stainless steel tube full welding 3 - gasket outer wall and second stainless steel tube full welding 4 - argon arc backing welding 5 - first layer of filling welding 6 - second layer of filling welding 7 - first stainless steel tube 8 - second stainless steel tube 9 - bevel 10 - inner chamfer 11 - gasket A - inlay length B - gap DETAILED DESCRIPTION

[0034] The present application discloses a kind of stainless steel pipe fixed welding opening argon arc welding back face not argon protection welding method.For those skilled in the art, process parameters can be improved appropriately by referring to the content herein.It is particularly pointed out that all similar substitutions and changes are obvious to those skilled in the art, and they are considered to be included in the present application.The method and application of the present application have been described by preferred embodiments, and relevant personnel can obviously modify or appropriately change and combine the method and application described herein without departing from the content, spirit and scope of the present application to realize and apply the present application technology.

[0035] As shown in Figure 1 , Figure 2 A kind of stainless steel pipe fixed welding opening argon arc welding back face not argon protection welding method, the method is suitable for 304, 316, 316L and other various stainless steel materials, the outer diameter of first stainless steel tube 7 and second stainless steel tube 8 to be welded is all φ159~φ630, specifically including the following steps:

[0036] 1) material preparation: stainless steel welding wire φ2.0mm, stainless steel gasket 11 (thickness is 3~4mm).Gasket 11 material selects the same material as pipe, because the welding quality of dissimilar materials is not good to control.

[0037] 2) gasket 11 production: the thickness of 3~4mm stainless steel plate material is rolled into the same size as the inner diameter of the stainless steel pipe to be welded and welded, and the weld is polished to the same thickness as the gasket, smooth transition;Or purchase the stainless steel pipe with the same size as the inner diameter of the stainless steel pipe to be welded, and cut into 40~50mm length for standby.

[0038] 3) bevel processing: the right end of first stainless steel tube 7 and the left end of second stainless steel tube 8 are processed bevel 9, and stainless steel tube is polished one side 30 ° bevel with angle grinder, and 1mm blunt edge is reserved and inner chamfer 45 °.Inner chamfer 45 ° makes gasket 11 outer wall and stainless steel tube inner wall contact tightly after welding without gap, which facilitates root penetration, and prevents local incomplete penetration defects at root.

[0039] 4) use alcohol or acetone solution, and clean the oil stains of stainless steel tube 100mm away from bevel on both sides and gasket 11.It can effectively improve the welding quality.

[0040] 5) Heat the first stainless steel pipe 7 around the bevel at a temperature below 100°C using an oxy-acetylene torch at a distance of about 100mm. Insert the left end of the stainless steel washer 11 into the right end of the first stainless steel pipe 7, with an insertion length A of about 20mm. As the temperature drops, the washer 11 will be in close contact with the pipe (first stainless steel pipe 7) without any gaps.

[0041] 6) At the full weld joint 1 between the gasket and the first stainless steel pipe, the end of the gasket 11 is fully welded to the first stainless steel pipe 7 in the direction of medium flow by argon arc welding without welding wire. The weld height is less than or equal to the thickness of the gasket 11. The purpose is to prevent impurities from remaining inside the pipeline after flushing and purging.

[0042] 7) At the point where the outer wall of the gasket is fully welded to the first stainless steel pipe, weld a full circle using argon arc welding. The current should not be too high (90-100A). Do not add welding wire; allow it to melt naturally. Excessive current can easily cause the gasket to melt through, resulting in weld oxidation and carburization, which will affect the quality of non-destructive testing of the weld.

[0043] 8) such as Figure 2 As shown, the weld assembly is as follows: The left end of the second stainless steel pipe 8 is heated by a gas welding gun at a distance of 100mm from the weld, and the temperature is below 100℃. The right side of the prefabricated washer 11 is then inserted into it. The gap B between the bevels of the first stainless steel pipe and the bevel of the first stainless steel pipe is 3-4mm.

[0044] After the temperature drops, the outer wall of gasket 11 will be in close contact with the inner wall of the stainless steel pipe (second stainless steel pipe 8) without any gaps. The full weld 3 between the outer wall of gasket 11 and the second stainless steel pipe will be welded around the entire circumference using argon arc welding with a current of 90-100A. Similarly, no welding wire will be added to allow it to self-melt until it melts.

[0045] 9) Root pass welding: After the weld seam is assembled, perform root pass welding at point 4 of the argon arc welding, with a current of 90-100A, and then add welding wire to fuse the weld.

[0046] 10) Topcoat welding: After the root pass welding is completed, perform filler welding at point 5 of the first layer, with a current of 100-110A. If the pipe wall thickness is large, filler welding can be performed at point 6 of the second layer.

[0047] Compared with the prior art, the present invention can be applied to pipes with a minimum diameter of φ159 because welding wire is not required in step 6). The argon arc welding gun is simply inserted into the pipe to allow the pipe to melt itself. In contrast, the prior art requires welding wire and cannot be used for small pipe diameters.

[0048] Compared with the prior art, the single edge of the stainless steel pipe is polished by 30° beveling with an angle grinder, 1mm root face is reserved and 45° internal chamfering is performed. The advantage of the "internal chamfering" is that the outer wall of the gasket is in close contact with the inner wall of the stainless steel pipe after welding without leaving a gap, which facilitates root penetration and prevents the root from having a local incomplete penetration defect.

[0049] In the present application, the stainless steel pipe is heated by a gas welding gun at a temperature lower than 100℃ around the welding opening about 100mm away from the welding opening, and the stainless steel gasket is inserted into the pipe about 20mm. When the temperature drops, the gasket is in close contact with the pipe without a gap. Compared with the prior art, the advantage of "thermal expansion and cold contraction" is that the gasket is in close contact with the pipe without a gap, and the weld does not oxidize.

[0050] The present application gives the welding current range value in multiple places, which is to prevent the current from being too large to easily cause the gasket and pipe to melt and penetrate, resulting in welding oxidation and carburizing, thereby affecting the quality of the weld non-destructive testing.

[0051] In the present application, the stainless steel pipe and the gasket are self-melted by argon arc welding without welding wire, the end of the gasket is fully welded together with the stainless steel pipe according to the medium flow direction, and the weld height is less than or equal to the thickness of the gasket. The purpose is to prevent impurities from remaining in the pipe after flushing and purging.

[0052] Compared with the prior art, the advantage of "fully welding the end of the gasket together with the stainless steel pipe according to the medium flow direction" is that "only one side of the two sides of the end of the gasket is in contact with the stainless steel pipe, and the welding side is the direction of medium inflow, and the non-welding side is the direction of outflow, which avoids the accumulation of impurities during flushing and purging, and affects the cleanliness of the pipe interior." Step 10) is an arc welding cover surface, which is fast and efficient. The prior art is full argon arc welding, which is low in efficiency.

[0053]

EXAMPLE

[0054] As shown in Figure 1 , Figure 2 , in this embodiment, the welding of stainless steel pipes in the external network pipe gallery in a certain metallurgical engineering is taken as an example. The stainless steel pipe material is 304, and the specification is φ219x6. The welding method is full argon arc welding.

[0055] The specific operation is as follows:

[0056] 1) Material preparation: first stainless steel pipe 7 (left stainless steel pipe) and second stainless steel pipe 8 (right stainless steel pipe) (material 304, specification φ219x6), stainless steel welding wire (material ER304, diameter φ2.0mm), stainless steel gasket 11 (material 304, δ=3mm plate).

[0057] 2) Gasket 11 fabrication: A 3mm thick stainless steel plate is coiled into a size equal to the inner diameter of the stainless steel pipe to be welded (219-6 x 2 = 207mm) using a plate coiling machine and welded. The weld is ground to a height equal to the gasket thickness (3mm), smoothed, and cut into lengths of 40-50mm for use.

[0058] 3) Groove machining: The right end of the first stainless steel pipe 7 and the left end of the second stainless steel pipe 8 are machined to have a groove. The first stainless steel pipe 7 and the second stainless steel pipe 8 are ground to have a single 30° groove using an angle grinder, with 1mm of a blunt edge left and an inner chamfer of 45°.

[0059] 4) The first stainless steel pipe 7 and the second stainless steel pipe 8 are cleaned of oil and dirt 100mm from the weld on both sides and at the gasket 11 using an alcohol or acetone solution.

[0060] 5) The right end of the first stainless steel pipe 7 is heated around the weld 100mm away using a gas welding torch at a temperature below 100°C. The stainless steel gasket 11 is inserted into the first stainless steel pipe 7 for a length A of 20mm. When the temperature drops, the gasket 11 is in close contact with the first stainless steel pipe 7 without any gaps.

[0061] 6) The left end of the gasket 11 and the right end of the first stainless steel pipe 7 are fully welded together in the direction of medium flow using argon arc welding without a welding wire, with the first stainless steel pipe 7 and the gasket 11 self-fusing. The weld height is less than or equal to the gasket thickness.

[0062] 7) The outer wall of the gasket and the first stainless steel pipe are fully welded at weld 2 using argon arc welding without a welding wire, with a current of 90-100A. The weld is self-fused when it melts.

[0063] 8) Weld joint assembly: The other side of the weld of the second stainless steel pipe 8 to be welded is heated for one turn 100mm from the weld using a gas welding torch at a temperature below 100°C. The other side of the pre-fabricated gasket is inserted into it, with a gap B of 3-4mm left, as shown in Figure 2 When the temperature drops, the outer wall of the gasket 11 is in close contact with the inner wall of the second stainless steel pipe 8 without any gaps.

[0064] The outer wall of the gasket and the second stainless steel pipe are fully welded at weld 3 using argon arc welding with a current of 90-100A. The weld is self-fused without a welding wire, and is ready when it melts.

[0065] 9) Base welding: After the weld joint assembly is complete, base welding is performed at weld 4 using argon arc welding with a current of 90-100A and a welding wire. The weld is ready when it melts.

[0066] 10) Cover welding: after the completion of the backing welding, the first layer of the filler welding is carried out at the filling welding position 5, and the current is 100-110 A. Since the pipe wall thickness is 6 mm, three layers of welding are required, and after the completion of the first layer of the filler welding at the filling welding position 5, the second layer of the filler welding is carried out at the filling welding position 6.

[0067] In the implementation of the improved stainless steel pipe fixed welding opening argon arc welding back non-argon protection welding method of the present application, the following points need to be paid attention to:

[0068] 1) The pipe distance welding opening 100 mm must be heated, and the temperature cannot be too high to cause the change of the material quality, and the gasket and the pipe are tightly connected by using the principle of thermal expansion and cold contraction, and there is no gap. In order to prevent air from entering to cause welding oxidation and carburization, and affect the welding quality.

[0069] 2) The gasket and the first stainless steel pipe full welding position 1 must be full welded according to the medium flow direction, so as to prevent dirt from entering and remaining in the pipe during pipe flushing and blowing.

[0070] 3) The backing welding current must not be too large, so as to prevent the gasket from being burned and oxidized and carburized.

[0071] 4) The interlayer temperature needs to be controlled to be not more than 150 DEG C, and the temperature that is too high will affect the welding quality.

[0072] The present application adopts the principle of thermal expansion and cold contraction to make the gasket 11 and the inner wall of the stainless steel pipe tightly contact and have no gap, and the molten pool is isolated from the air during the assembly and welding of the stainless steel fixed welding opening, so as to avoid the oxidation and carburization of the weld, solve the problem of argon arc backing welding in long-distance stainless steel pipe and stainless steel pipe maintenance operation, prevent the oxidation and carburization of the back of the weld, improve the welding efficiency, and the weld quality is excellent, and it is easy to meet the requirements of the specification and the design document.

[0073] The above is only the preferred specific embodiment of the present application, but the protection scope of the present application is not limited to this, any skilled person in the art can make equivalent replacement or change according to the technical scheme and the inventive concept of the present application within the technical range disclosed by the present application, which should be covered in the protection scope of the present application.

Claims

1. A method of welding a stainless steel pipe by argon arc welding from the back side without argon shielding, characterized in that, Specifically comprising the following steps: 1) machining a bevel on the end of the first stainless steel pipe and the end of the second stainless steel pipe to be welded; the bevel is 20-40°, leaving a root face, and the inside chamfer is 30-50°; 2) making a gasket, the gasket being made of the same material as the first stainless steel pipe and the second stainless steel pipe, the gasket being tubular, and the outer diameter of the gasket being equal to the inner diameter of the first stainless steel pipe and the second stainless steel pipe; 3) heating the end of the first stainless steel pipe, inserting one end of the gasket into the first stainless steel pipe from the end, and after cooling, the gasket is in close contact with the inner wall of the first stainless steel pipe without any gap; the heating temperature is lower than 100℃, and a gas welding gun is used to heat at 100±20mm from the bevel; 4) using argon arc welding without welding wire, the gasket and the first stainless steel pipe are fully welded together in the medium flow direction by self-melting, and the weld height is less than or equal to the thickness of the gasket; 5) using argon arc welding to weld the bevel of the first stainless steel pipe for one turn; the argon arc welding current is 90-100A; the welding wire used is made of the same material as the first stainless steel pipe and the second stainless steel pipe; 6) heating the end of the second stainless steel pipe, inserting the other end of the gasket into the second stainless steel pipe, and after cooling, the gasket is in close contact with the inner wall of the second stainless steel pipe without any gap; the heating temperature is lower than 100℃, and a gas welding gun is used to heat at 100±20mm from the bevel; the gap between the bevel of the first stainless steel pipe and the bevel of the first stainless steel pipe is 3-4mm; 7) performing backing welding on the inside of the bevel of the first stainless steel pipe and the second stainless steel pipe, and performing filling welding on the outside; the welding current is 90-100A; if the thickness of the first stainless steel pipe and the second stainless steel pipe is greater than 5mm, the filling welding is multi-layered.

2. The method of welding a stainless steel pipe according to claim 1, wherein The step 2) further comprises using alcohol or acetone solution to clean the oil stains on the end of the first stainless steel pipe and the end of the second stainless steel pipe and the gasket.

3. The method of welding a stainless steel pipe according to claim 1, wherein The thickness of the gasket in the step 2) is 3-4mm.

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