Welding method for surfacing transition layer at end part of heat exchanger cylinder

Abstract

The invention discloses a welding method for a surfacing transition layer at the end of a heat exchanger barrel, and relates to the technical field of heat exchanger manufacturing, in particular to the welding method for the surfacing transition layer at the end of the heat exchanger barrel for butt joint of dissimilar steel barrel sections. The invention aims to solve the surfacing defects of the traditional vertical surfacing method. The method comprises the following steps: 1, pretreating the end part of the high-grade material shell ring of the heat exchanger; secondly, process rings of the same specification are prepared and assembled, and a welding flux baffle ring is installed on the inner side of the surfacing position; thirdly, surfacing operation is conducted in a girth welding mode; fourthly, the weld joint obtained after surfacing is subjected to polishing treatment; 5, carrying out overall heat treatment on the shell ring; and sixthly, the end of the shell ring is marked according to the design size, the allowance is removed through gas cutting, a groove is formed through turning, and assembling and circumferential weld welding of the shell ring and the low-alloy steel or carbon steel shell ring are completed. The method is suitable for large-scale production of butt joint of dissimilar steel cylinders and has remarkable popularization value.

Description

Technical Field

[0001] This invention relates to the field of heat exchanger manufacturing technology, and specifically to a welding method for overlaying a transition layer at the end of a heat exchanger shell for connecting sections made of dissimilar steel materials. Background Technology

[0002] In high-performance heat exchanger products, due to the varying heating temperatures of different parts of the shell, the shell is typically designed with a combination of different materials to optimize costs; one end of the shell is made of low-alloy steel or carbon steel, while the other end is made of a high-grade material. However, the performance differences between the two materials are significant. Directly butt-welding the shell will result in uneven stress on the weld, reduced corrosion resistance, and a "dilution" phenomenon that lowers the proportion of alloying elements in the weld. Furthermore, the heat treatment temperature ranges of the two materials differ significantly, with no overlap. Direct butt welding cannot achieve effective overall heat treatment, severely impacting product quality.

[0003] To solve the above problems, the existing technology adopts the method of overlaying a transition layer on the end of the high-grade material cylinder section. However, the traditional overlaying method is vertical wire electrode submerged arc welding. The specific process is as follows: machining the end face of the cylinder section according to the drawing dimensions → installing flux retaining rings on the inner and outer sides of the end of the cylinder section to be overlaid and clamping them on the positioner → using a manipulator to perform wire electrode submerged arc welding → removing the retaining rings and performing local repair welding → machining the overlaying allowance and end beveling → surface magnetic particle inspection or dye penetrant testing → overall heat treatment and re-inspection of the cylinder section.

[0004] This traditional vertical welding method has many drawbacks:

[0005] The flux retaining ring is welded to the cylinder boundary. Welding stress can easily cause deformation of the backing plate. Combined with the ellipticity and edge angles of the cylinder itself, gaps will be generated at the junction of the cylinder and the backing plate, leading to weld defects. When welding high-grade material cylinder sections to the backing plate, if the preheating temperature is insufficient, cracks and other defects are very likely to occur, increasing the amount of subsequent rework. Due to the ellipticity of the cylinder roll, the inner and outer circles need to be ground to remove excess material after machining, resulting in low processing efficiency. The weld overlay is thin, and only surface inspection can be performed. Deep inspections such as ultrasonic and radiographic testing are not possible, which poses a risk that defects at the weld overlay interface will not be detected. Furthermore, if problems are found after the weld is formed, they cannot be repaired, leading to weld failure. Summary of the Invention

[0006] To address the shortcomings of existing vertical overlay welding methods, this invention provides a welding method for overlaying a transition layer at the end of a heat exchanger shell.

[0007] The welding method for the overlay transition layer at the end of a heat exchanger shell according to the present invention is completed according to the following steps:

[0008] The welding method for the overlay transition layer at the end of the heat exchanger shell is completed according to the following steps:

[0009] 1. Pre-treat the ends of the high-grade material cylinder sections of the heat exchanger;

[0010] 2. Prepare process rings of the same specifications, assemble the process rings with the pre-treated cylinder end, and install flux retaining rings on the inner side of the welding position;

[0011] 3. The surfacing operation is carried out using circumferential seam welding; the surfacing process is completed in one step using automatic circumferential seam welding technology.

[0012] 4. Grind the weld after overlay welding, and then perform non-destructive testing to ensure that the overlay layer passes the test.

[0013] 5. Perform overall heat treatment on the cylinder section, and after the heat treatment is completed, perform non-destructive testing again to ensure that the test results are qualified;

[0014] 6. Mark the ends of the cylinder section according to the design dimensions, remove the excess material by gas cutting, and then machine the bevel to complete the assembly with the low alloy steel or carbon steel cylinder section and the circumferential weld.

[0015] Beneficial effects of this invention:

[0016] This invention employs a simulated circumferential welding method, which makes preheating more convenient, the welding process mature, and the weld formation quality stable, effectively solving the problem of insufficient preheating in vertical surfacing welding. Through multi-dimensional non-destructive testing, this invention can comprehensively detect surface and internal defects in the weld overlay layer, avoiding the limitations of traditional processes that only allow surface inspection and improving testing reliability. Subsequent scribing, gas cutting, and beveling operations are simple, requiring no additional grinding allowance, reducing processing difficulty and improving production efficiency.

[0017] It completely solves the problem of crack defects at the fusion line between the retaining ring and the cylinder in vertical overlay welding, reduces the amount of rework, and has passed the verification of multiple products on the first try. The quality is stable and reliable, and it is suitable for the large-scale production of dissimilar steel cylinders. It has significant promotional value. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the outer shell connection; 1 is a low-alloy steel or carbon steel cylinder section, and 2 is a high-grade material cylinder section;

[0019] Figure 2 A schematic diagram of the installation of an existing vertical flux retaining ring for overlay welding;

[0020] Figure 3 A schematic diagram of the vertical overlay welding operation at the end of the cylinder;

[0021] Figure 4 This is a schematic diagram simulating horizontal overlay welding.

[0022] Figure 5This is a schematic diagram of a horizontal welding operation. Detailed Implementation

[0023] The technical solution of the present invention is not limited to the specific embodiments listed below, but also includes any combination of the specific embodiments.

[0024] Specific Implementation Method 1: The welding method for the overlay transition layer at the end of a heat exchanger shell according to this embodiment is completed according to the following steps:

[0025] The welding method for the overlay transition layer at the end of the heat exchanger shell is completed according to the following steps:

[0026] 1. Pre-treat the ends of the high-grade material cylinder sections of the heat exchanger;

[0027] 2. Prepare process rings of the same specifications, assemble the process rings with the pre-treated cylinder end, and install flux retaining rings on the inner side of the welding position;

[0028] 3. The surfacing operation is carried out using circumferential seam welding; the surfacing process is completed in one step using automatic circumferential seam welding technology.

[0029] 4. Grind the weld after overlay welding, and then perform non-destructive testing to ensure that the overlay layer passes the test.

[0030] 5. Perform overall heat treatment on the cylinder section, and after the heat treatment is completed, perform non-destructive testing again to ensure that the test results are qualified;

[0031] 6. Mark the ends of the cylinder section according to the design dimensions, remove the excess material by gas cutting, and then machine the bevel to complete the assembly with the low alloy steel or carbon steel cylinder section and the circumferential weld.

[0032] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that the pretreatment described in step one involves flattening the end of the cylinder section to the net dimensions or beveling it at a 5° angle on the outside. Everything else is the same as in Specific Implementation Method One.

[0033] Specific Implementation Method 3: This implementation method differs from Specific Implementation Method 1 in that a gap of 5-10mm is left when assembling the process ring with the pre-treated cylinder end in step 2. Everything else is the same as in Specific Implementation Method 1.

[0034] Specific Implementation Method Four: This implementation method differs from Specific Implementation Method One in that the welding area is preheated before the welding operation in step three. Everything else is the same as in Specific Implementation Method One.

[0035] Specific Implementation Method Five: This implementation method differs from Specific Implementation Method One in that post-heating or hydrogen removal treatment is performed after the welding operation in step three. Everything else is the same as in Specific Implementation Method One.

[0036] Specific Implementation Method Six: This implementation method differs from Specific Implementation Method One in that the non-destructive testing described in step four employs a combination of ultrasonic testing, radiographic testing, and magnetic particle or dye penetrant testing. Everything else is the same as in Specific Implementation Method One.

[0037] The beneficial effects of the present invention are verified by the following embodiments:

[0038] Example 1: A high-grade material cylinder section of a high-performance heat exchanger is joined with a carbon steel cylinder section using the welding method of the present invention. The steps are as follows:

[0039] The ends of the high-grade material cylinder sections are machined flat to ensure that the flatness error of the ends is ≤0.2mm;

[0040] Prepare process rings of the same specifications, assemble the process rings with the end of the cylinder section, leave an 8mm gap, and install a special flux retaining ring on the inner side of the weld overlay.

[0041] Preheat the welding area to 150~200℃ before welding, and use wire submerged arc circumferential automatic welding to build up the transition layer in one step. After welding, perform hydrogen removal treatment.

[0042] Grind the weld surface until it is smooth and free of spatter, and then perform ultrasonic testing, radiographic testing, and magnetic particle or dye penetrant testing in sequence. The test results all meet the Class I requirements of NB / T47013 standard.

[0043] The entire cylinder section undergoes heat treatment, and is then re-tested to ensure it passes inspection.

[0044] According to the design dimensions, the excess material is removed by gas cutting, and a V-shaped bevel is machined. After assembly with the carbon steel cylinder section, a circumferential weld is welded, and the final weld inspection is qualified.

[0045] This invention constructs a "virtual docking structure": At the end of a high-grade material cylindrical section requiring a transition layer, a "process ring" (material not limited, compatible with the same specifications) is added, with a 5-10mm gap reserved. Simultaneously, a flux retaining ring is installed inside. At this point, the "cylinder end + process ring + flux retaining ring" form a complete "ring-shaped docking joint" (similar to the structure of two actual cylindrical sections docking). Utilizing mature circumferential welding equipment and processes: the assembled "cylinder section + process ring" is clamped onto a roller frame. The weld overlay is equivalent to a "circumferential weld": during welding, the deposited metal fills the gap between the cylindrical section end and the process ring, as well as the surface of the cylindrical section end. The resulting weld overlay is essentially part of the "circumferential weld" (the process ring needs to be removed by gas cutting later, retaining the transition layer at the cylindrical section end).

Claims

1. A welding method for a transition layer overlaid at the end of a heat exchanger shell, characterized in that... The welding method for the overlay transition layer at the end of the heat exchanger shell is completed according to the following steps:

1. Pre-treat the ends of the high-grade material cylinder sections of the heat exchanger; 2. Prepare process rings of the same specifications, assemble the process rings with the pre-treated cylinder end, and install flux retaining rings on the inner side of the welding position; 3. The surfacing operation is carried out using circumferential seam welding; the surfacing process is completed in one step using automatic circumferential seam welding technology.

4. Grind the weld after overlay welding, and then perform non-destructive testing to ensure that the overlay layer passes the test.

5. Perform overall heat treatment on the cylinder section, and after the heat treatment is completed, perform non-destructive testing again to ensure that the test results are qualified; 6. Mark the ends of the cylinder section according to the design dimensions, remove the excess material by gas cutting, and then machine the bevel to complete the assembly with the low alloy steel or carbon steel cylinder section and the circumferential weld.

2. The welding method for the overlay transition layer at the end of a heat exchanger shell according to claim 1, characterized in that... The pretreatment described in step one involves flattening the end of the cylinder section to the net dimensions or beveling it at a 5° angle on the outside.

3. The welding method for the overlay transition layer at the end of a heat exchanger shell according to claim 1, characterized in that... In step two, when assembling the process ring with the pre-treated cylinder end, a gap of 5-10mm should be reserved.

4. The welding method for the overlay transition layer at the end of a heat exchanger shell according to claim 1, characterized in that... In step three, the welding area is preheated before the welding operation.

5. The welding method for the overlay transition layer at the end of a heat exchanger shell according to claim 1, characterized in that... After the welding operation in step three is completed, post-heating or hydrogen removal treatment is performed.

6. The welding method for the overlay transition layer at the end of a heat exchanger shell according to claim 1, characterized in that... The non-destructive testing described in step four is performed using ultrasonic testing, radiographic testing, magnetic particle testing, or dye penetrant testing.

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