Welding method for 304L stainless steel tubular pressure vessel for ultra-low temperature environment

Abstract

A welding method for 304L stainless steel tubular pressure vessels used in cryogenic environments is disclosed, relating to the field of welding. The welding method for 304L stainless steel tubular pressure vessels used in cryogenic environments includes the following steps: vertically assembling and welding the various sections of the pressure vessel using tungsten inert gas (TIG) welding for the root pass and shielded metal arc welding (SMAW) for the fill and cover passes, controlling the Ni content in the welding wire and electrode to be 17-18% and the Mo content ≤0.5%; after the welded sections are sandblasted and pickled for passivation, they are horizontally installed on a foundation for the closure weld of the various sections, controlling the Ni content in the welding wire and electrode to be 17-18%, the Mn content to be 5-6%, and the Mo content ≤0.5%. This welding method for 304L stainless steel tubular pressure vessels used in cryogenic environments solves the problems of low impact energy absorption at -196℃, poor weld quality, and low first-pass yield during on-site assembly welding of 304L tubular pressure vessels.

Description

Technical Field

[0001] This application relates to the field of welding, and more specifically, to a welding method for 304L stainless steel tubular pressure vessels used in cryogenic environments. Background Technology

[0002] 304L austenitic stainless steel has high strength and excellent low-temperature toughness and plasticity. At the same time, due to its low carbon content, it has excellent corrosion resistance and is often used as a low-temperature steel, such as domestically produced ultra-low temperature liquid storage and transportation containers, with an operating temperature of -196 to -183℃.

[0003] Tubular pressure vessels are tubular cylindrical bodies, typically one or a combination of cylindrical, conical, and hyperboloidal cylindrical bodies. They are generally constructed using on-site fabrication and installation methods. This involves dividing the tubular pressure vessel into several sections, each prefabricated and vertically assembled on-site, then horizontally assembled on a foundation, and finally welding the joints between the sections. For some tubular pressure vessels operating under cryogenic conditions (using liquid nitrogen as the operating medium), 304L stainless steel is used as the main material. Due to the harsh operating environment, high performance requirements are placed on the welded joints, requiring an impact absorption energy (KV2) of 60J or higher at -196℃.

[0004] For 304L austenitic stainless steel, welding materials with the chemical composition classification code 308L are typically used. The average impact absorption energy (KV2) of the deposited metal at -196℃ is around 30J, far below the performance requirements for welded joints of 304L tubular pressure vessels used in cryogenic environments. When these vessels are horizontally assembled on a foundation, the axes and elevations of each section need to be adjusted. Therefore, the assembly quality of the final weld is far inferior to the assembly quality of the welds from the prefabrication stage of each section. Conventional techniques cannot guarantee a high first-pass yield for the final weld, resulting in a large amount of rework.

[0005] Therefore, a welding method for 304L stainless steel tubular pressure vessels used in ultra-low temperature environments is needed to solve the aforementioned problems. Summary of the Invention

[0006] The purpose of this application is to provide a welding method for 304L stainless steel tubular pressure vessels used in ultra-low temperature environments, which solves the problems of low impact absorption energy of welds at -196℃, poor weld quality, and low first-pass yield when assembling 304L tubular pressure vessels on site.

[0007] This application is implemented as follows:

[0008] This application provides a welding method for 304L stainless steel tubular pressure vessels used in cryogenic environments, which includes the following steps:

[0009] The various sections of the pressure vessel are vertically assembled and welded; the welding method is tungsten inert gas welding for the root pass and shielded metal arc welding for the fill and cover passes; ER317L welding wire and E317L-15 welding rod are selected, and the mass percentage content of Ni in the welding wire and welding rod is controlled to be 17-18%, and the mass percentage content of Mo is ≤0.5%.

[0010] After the welded sections are sandblasted, pickled and passivated, they are horizontally installed on the foundation.

[0011] Perform the closure welds for each section: When the assembly gap is 2-6mm, the welding method is tungsten inert gas (TIG) welding for the root pass and shielded metal arc welding (SMAW) for the fill and cover passes; when the assembly gap is less than 2mm or greater than 6mm, the welding method is SMAW welding for the root pass and SMAW welding for the fill and cover passes; ER317L welding wire and E317L-15 welding rod are selected, and the mass percentage content of Ni in the welding wire and welding rod is controlled to be 17-18%, the mass percentage content of Mn is 5-6%, and the mass percentage content of Mo is ≤0.5%.

[0012] In some alternative implementations, before sandblasting, pickling and passivation of each segment, the bevels at the front and rear ends of the segment are ground clean. After sandblasting, pickling and passivation of each segment, the bevels at the front and rear ends of the segment are ground a second time to remove the passivation film.

[0013] In some alternative implementations, each segment is fixed to the foundation by grouting before the closure welds are welded together.

[0014] In some alternative implementations, when the closing weld is performed using shielded metal arc welding (SMAW) for the root pass and SMAW for the filler and cover passes, carbon arc gouging is used to clean the root after the root pass is completed. The root cleaning is performed on the reverse side of the root pass.

[0015] In some alternative implementations, when installing the welded sections onto the foundation, the elevation and axis of each section are first adjusted to the acceptable range. Then, the assembly quality of the weld joint of each section is adjusted to make the gap, misalignment, and step difference values ​​at each point of the weld joint equal. Finally, the elevation and axis of each section are adjusted again to the acceptable range.

[0016] In some alternative implementations, after the closure weld is completed, the weld is ground, the location of the undercut is marked, and the undercut is repaired using gas tungsten inert welding.

[0017] In some alternative implementations, when performing vertical assembly welding, 1.5 to 3.5% by volume H2 is added to the shielding gas.

[0018] In some alternative implementations, when performing the closing weld, 1.5 to 3.5% by volume H2 is added to the shielding gas.

[0019] The beneficial effects of this application are as follows: The welding method for 304L stainless steel tubular pressure vessels used in ultra-low temperature environments provided by this application includes the following steps: vertically assembling and welding the various sections of the pressure vessel; the welding method is tungsten inert gas welding for the root pass and shielded metal arc welding for the fill and cover passes; ER317L welding wire and E317L-15 welding rod are selected, and the mass percentage content of Ni in the welding wire and welding rod is controlled to be 17-18%, and the mass percentage content of Mo is ≤0.5%; after the welding is completed, the various sections are sandblasted, pickled and passivated, and then horizontally installed. Based on this, the closure welds of each section are performed: when the assembly gap is 2-6mm, the welding method is tungsten inert gas (TIG) welding for the root pass and shielded metal arc welding (SMAW) for the fill and cover passes; when the assembly gap is less than 2mm or greater than 6mm, the welding method is SMAW welding for the root pass and SMAW welding for the fill and cover passes; ER317L welding wire and E317L-15 welding rod are used, and the mass percentage content of Ni in the welding wire and welding rod is controlled to be 17-18%, the mass percentage content of Mn to be 5-6%, and the mass percentage content of Mo to be ≤0.5%. The welding method for 304L stainless steel tubular pressure vessels in ultra-low temperature environments provided in this application solves the problems of low impact absorption energy of welds at -196℃, poor weld quality, and low first-pass yield when assembling 304L tubular pressure vessels on site. Attached Figure Description

[0020] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 A schematic diagram illustrating the vertical assembly and welding of various sections in the welding method for a 304L stainless steel tubular pressure vessel used in an ultra-low temperature environment provided in the embodiments of this application.

[0022] Figure 2 A schematic diagram of the horizontal closure weld of each section in the welding method of the 304L stainless steel tubular pressure vessel for cryogenic environment provided in the embodiments of this application.

[0023] Figure 3 Microscopic metallographic image of the weld seam of the tubular pressure vessel obtained by the welding method of 304L stainless steel tubular pressure vessel in ultra-low temperature environment provided in the embodiments of this application.

[0024] In the diagram: 100, section; 200, closure weld. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. The components of the embodiments of this application described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0026] Therefore, the following detailed description of the embodiments of this application provided in the accompanying drawings is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments of the application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0027] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0028] In the description of this application, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of this application is in use. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on this application. In addition, the terms "first," "second," and "third," etc., are only used to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0029] Furthermore, terms such as "horizontal," "vertical," and "sag" do not imply that components must be absolutely horizontal or suspended, but rather that they can be slightly tilted. For example, "horizontal" simply means that its direction is more horizontal relative to "vertical," and does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0030] In the description of this application, it should also be noted that, unless otherwise expressly specified and limited, the terms "set up," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0031] In this application, unless otherwise expressly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature being directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature being directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0032] The following describes in further detail the features and performance of the welding method for 304L stainless steel tubular pressure vessels in cryogenic environments according to this application, with reference to specific embodiments.

[0033] like Figure 1 and Figure 2 As shown in the figure, this application provides a welding method for 304L stainless steel tubular pressure vessels used in cryogenic environments, which includes the following steps:

[0034] Step S1: Vertically assemble and weld the various sections of the pressure vessel; the welding method is tungsten inert gas (TIG) welding for the root pass and shielded metal arc welding (SMAW) welding for the fill and cover passes; ER317L welding wire is selected, and its chemical composition conforms to GB / T 29713 standard; E317L-15 welding electrode is selected, and its chemical composition conforms to GB / T 983 standard; the mass percentage content of Ni in the welding wire and electrode is controlled to be 17-18%, and the mass percentage content of Mo is ≤0.5%; when vertically assembling and welding the various sections of the pressure vessel, 1.5-3.5% by volume H2 is added to the shielding gas;

[0035] Step S2: After sandblasting and pickling passivation of each welded section, rotate it 90 degrees and install it horizontally on the foundation. When installing each welded section on the foundation, first adjust the elevation and axis of each section to the acceptable range, then adjust the assembly quality of the weld joint to ensure that the gap, misalignment, and step difference values ​​are equal at all points of the weld joint, and finally adjust the elevation and axis of each section to the acceptable range again. Before sandblasting and pickling passivation of each section, clean the bevels at the front and rear ends of each section. After sandblasting and pickling passivation, clean the bevels at the front and rear ends of each section a second time to remove the passivation film.

[0036] Step S3: Perform the closure weld of each section: When the assembly gap is 2-6mm, the welding method is tungsten inert gas (TIG) welding for the root pass and shielded metal arc welding (SMAW) for the fill and cover passes; when the assembly gap is less than 2mm or greater than 6mm, the welding method is SMAW welding for the root pass and SMAW welding for the fill and cover passes; ER317L welding wire is selected, and its chemical composition conforms to GB / T 29713 standard; E317L-15 welding electrode is selected, and its chemical composition conforms to GB / T The 983 standard specifies that the mass percentage content of Ni in the welding wire and electrode should be 17-18%, the mass percentage content of Mn should be 5-6%, and the mass percentage content of Mo should be ≤0.5%. Before welding the closure weld of each section, grouting should be performed on each section to fix it to the foundation. When using shielded metal arc welding (SMAW) for the root pass and SMAW for the fill and cover passes, carbon arc gouging should be used to clean the root after the root pass, and this cleaning should be performed on the reverse side of the root pass. When welding the closure weld of each section, 1.5-3.5% by volume H2 should be added to the shielding gas. After the closure weld is completed, the welds of each section of the pressure vessel should be ground, the undercut locations should be marked, and the undercuts should be repaired using gas tungsten inert gas (GTIG) welding.

[0037] This application provides a welding method for 304L stainless steel tubular pressure vessels used in cryogenic environments. By adjusting the content of certain chemical elements in ER317L welding wire and E317L-15 welding rod, the low-temperature toughness of the weld metal can be significantly improved, enabling the weld to absorb an impact energy (KV2) of over 60J at -196℃. By employing different welding methods and processes for different assembly conditions at different locations of the closure weld, the first-pass yield of the weld can be effectively improved. By adjusting the manganese content in the welding material used for the closure weld, the resistance to hot cracking can be effectively improved, solving the problem of cracking easily occurring in the closure weld under high restraint stress during welding.

[0038] When vertically assembling and welding the various sections of the pressure vessel, the 304L stainless steel tubular pressure vessel for cryogenic environments is first divided into several sections 100 based on the site construction environment, layout, and lifting machinery capabilities. Each section 100 is then vertically assembled and welded, such as... Figure 1 As shown, tungsten inert gas (TIG) welding is used for the root pass, and shielded metal arc welding (SMAW) is used for the fill and cover passes. The welding wire used is a modified ER317L, with a Ni content of 17-18% by mass, a Mo content ≤0.5% by mass, and the remaining chemical elements conforming to GB / T 29713 standard. The welding electrode used is a modified E317L-15, with a Ni content of 17-18% by mass, a Mo content ≤0.5% by mass, and the remaining chemical elements conforming to GB / T 983 standard. 1.5-3.5% by volume H2 is added to the shielding gas for TIG welding. Test plates are welded simultaneously with the 100mm prefabrication of each section.

[0039] Welding materials with the chemical element classification code 317L can be used to weld 304L stainless steel. However, the impact absorption energy (KV2) of the weld metal of 317L welding materials on the market at -196℃ is about 35J. Although the low-temperature toughness of the weld metal of 317L welding materials is better than that of 308L welding materials, it is still difficult to meet the requirement of 60J impact absorption energy (KV2) at -196℃ for welding joints of 304L tubular pressure vessels in ultra-low temperature environments. Therefore, in this embodiment, the chemical composition of the 317L type welding material is improved by increasing the nickel content to significantly expand the austenite phase region, thereby improving the low-temperature toughness of the weld metal. The molybdenum content is reduced to decrease the formation and residue of ferrite and reduce the precipitation of σ phase at high temperatures, thereby improving the low-temperature toughness of the weld metal. At the same time, due to the increased nickel content in the welding material, the alloy content of the weld metal increases, which further reduces the fluidity of the weld pool and makes it easy for incomplete fusion defects to occur. Therefore, 1.5 to 3.5% by volume H2 is added to the shielding gas to increase the arc energy and increase the penetration depth to avoid incomplete fusion defects.

[0040] The welds of each section 100 after welding are ground down. For undercut defects, tungsten inert gas welding is used for repair. After non-destructive testing and rework, the bevels of the front and rear ends of each section 100 are ground clean to expose the metallic luster.

[0041] After grinding the weld, each section 100 undergoes sandblasting and pickling passivation treatment. Then, the bevels at the front and rear ends of each section 100 are ground a second time to remove the passivation film and expose the metallic luster. This is because 304L austenitic stainless steel, after sandblasting and pickling passivation, can maintain a consistent surface color, remove contaminants, and reform a passivation film. However, the passivation film can cause incomplete fusion defects. Therefore, after sandblasting and pickling passivation, each section 100 needs to undergo a second grinding to remove the passivation film to avoid incomplete fusion defects during welding.

[0042] like Figure 2 As shown, after welding and removing the passivation film, each segment 100 is rotated 90° and then horizontally installed on the foundation. During on-site installation, the elevation and axis of each segment 100 must first be guaranteed to be qualified, followed by the quality of the weld assembly. Therefore, the elevation and axis of each segment 100 are initially adjusted before adjusting the weld assembly parameters. To prevent the elevation and axis of each segment 100 from being unqualified after adjusting the weld assembly parameters, a secondary adjustment of the elevation and axis of each segment 100 is required. Ensuring that the gap, misalignment, and step difference values ​​at all points of the weld are basically equal is sufficient to guarantee the qualification of the elevation and axis of each segment 100, thus avoiding unstable weld assembly quality. By performing a grouting fixation on each segment 100, movement of the segment 100 during subsequent welding processes can be prevented from causing unqualified elevation and axis.

[0043] When welding the closure welds of the various sections 100 on the foundation, if the assembly gap of the closure weld 200 is 2-6 mm, tungsten inert gas (TIG) welding is used for the root pass, and shielded metal arc welding (SMAW) is used for the filler and cover passes. If the assembly gap of the closure weld 200 is less than 2 mm or greater than 6 mm, SMAW is used for the root pass, and after the root pass is completed, carbon arc gouging is used to clean the root on the reverse side of the root pass. This is because the assembly quality of the closure weld 200 is unstable, and the assembly gap, misalignment, and step difference values ​​are not the same at different locations. Therefore, different welding methods and processes are used for different assembly conditions.

[0044] When the gap between the weld pieces is small or large, tungsten inert gas (TIG) welding is inefficient and prone to cracking during the root pass. Therefore, shielded metal arc welding (SMAW) is used for the root pass, followed by carbon arc gouging for cleaning. Since cracks may occur on the reverse side of the weld during SMAW root pass, carbon arc gouging is performed on the reverse side of the weld. When the gap between the weld pieces is neither too large nor too small, ranging from 2 to 6 mm, TIG welding is still used for the root pass, avoiding the need for cleaning.

[0045] Because each section 100 underwent grouting after on-site installation, the restraint stress of the closure weld 200 is relatively high, making it prone to hot cracking during welding. Therefore, increasing the manganese content in the welding material for the closure weld 200 can both expand the austenite phase region to increase the low-temperature toughness of the weld metal and significantly improve the crack resistance of the weld. After the closure weld 200 is welded, the weld is ground, the undercut is marked, and the undercut is repaired using gas tungsten inert gas welding.

[0046] The product test plates processed by the welding method for 304L stainless steel tubular pressure vessels in ultra-low temperature environments provided in this application embodiment were tested, and the impact absorption energy KV2 of the weld at -196℃ was all above 74J, far exceeding the required 60J; Figure 3 As shown, the metallographic structure of the weld metal of the product processed by the welding method of 304L stainless steel tubular pressure vessel in ultra-low temperature environment is dendritic austenite and trace ferrite. The trace ferrite exists in the grain and grain boundary as small black dots in the figure. Since the ferrite content is very small, it improves the low temperature toughness of the weld metal.

[0047] The embodiments described above are some, but not all, of the embodiments of this application. The detailed description of the embodiments of this application is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

Claims

1. A welding method for 304L stainless steel tubular pressure vessels used in ultra-low temperature environments, characterized in that, It includes the following steps: The various sections of the pressure vessel are vertically assembled and welded; the welding methods are tungsten inert gas welding for the root pass and shielded metal arc welding for the fill and cover passes; ER317L welding wire and E317L-15 welding rod are selected, and the mass percentage content of Ni in the welding wire and welding rod is controlled to be 17~18%, and the mass percentage content of Mo is ≤0.5%; After the welded sections are sandblasted and pickled for passivation, they are horizontally installed on the foundation. Before sandblasting and pickling each section, the bevels at the front and rear ends of the sections are cleaned. After sandblasting and pickling each section, the bevels at the front and rear ends of the sections are ground a second time to remove the passivation film. Before welding the closure joints of each section, perform initial grouting of each section to fix it to the foundation. When installing the welded sections onto the foundation, first adjust the elevation and axis of each section to the acceptable range. Then adjust the assembly quality of the closure joints to ensure that the gaps, misalignments, and step differences at all points of the closure joint are equal. Finally, readjust the elevation and axis of each section to the acceptable range. When the assembly gap is 2-6mm, the welding method is tungsten inert gas (TIG) welding for the root pass and shielded metal arc welding (SMAW) for the filler pass. Face welding; when the assembly gap is less than 2mm or greater than 6mm, the welding method is shielded metal arc welding (SMAW) for the root pass and SMAW for the fill and cover passes; when the closure weld is welded using SMAW for the root pass and SMAW for the fill and cover passes, carbon arc gouging is used for root cleaning after the root pass is completed. The root cleaning is performed on the reverse side of the root pass weld; ER317L welding wire and E317L-15 welding rod are selected, and the mass percentage content of Ni in the welding wire and welding rod is controlled to be 17~18%, the mass percentage content of Mn is 5~6%, and the mass percentage content of Mo is ≤0.5%.

2. The welding method for 304L stainless steel tubular pressure vessels used in ultra-low temperature environments according to claim 1, characterized in that, After the closure weld is completed, grind the weld and mark the position of the undercut. Repair the undercut using gas tungsten inert gas welding.

3. The welding method for 304L stainless steel tubular pressure vessels used in ultra-low temperature environments according to claim 1, characterized in that, When performing vertical assembly welding, add 1.5~3.5% H2 by volume to the shielding gas.

4. The welding method for 304L stainless steel tubular pressure vessels used in ultra-low temperature environments according to claim 1, characterized in that, When performing closure welds, add 1.5 to 3.5% by volume H2 to the shielding gas.

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