Method for beveling and welding longitudinal and circumferential seams of large diameter vessels

Abstract

Beveling and welding methods used for longitudinal and circumferential seams of large-diameter vessels. Existing large-diameter, thick-walled Class 347H pressure vessels operate under high temperature and high Cl- content. ‑ This invention addresses the phenomenon of cracks forming during operation in certain environments. It employs a double-sided U-shaped bevel welded to the inner and outer sides of a container, with a gap between the two U-shaped bevels. Grooves are machined inside the container body, and welding is performed within these grooves. The U-shaped bevels have unequal thicknesses on both sides, with the deeper U-shaped bevel side having a depth 0.6-0.7 times the container wall thickness. This invention relates to the beveling and welding methods for longitudinal and circumferential seams in large-diameter containers.

Description

Technical Field

[0001] This invention relates to a beveling and welding method for longitudinal and circumferential seams of large-diameter containers. Background Technology

[0002] When the operating temperature of a large-diameter, thick-walled pressure vessel exceeds 525℃, and the medium inside the vessel has a high concentration of Cl... - When considering allowable stress calculations and the operating medium, nickel-based materials (INCONEL 600 or INCONEL 800, etc.) are generally chosen as the material for the main shell of pressure vessels. In recent years, to reduce operating costs, design institutes have gradually begun to use 347H-type high-carbon austenitic stainless steel containing stabilizing elements instead of nickel-based materials under the same operating conditions. Although the use of 347H-type stainless steel reduces raw material costs by approximately 50%-60%, 347H-type pressure vessels have limitations in high-temperature and Cl-related applications. - Under the combined effects of stress corrosion and other factors, through-cracks frequently appear in the weld seams of products during operation. Preliminary analysis indicates that these cracks are caused by stress corrosion, and their formation is also closely related to the selection of beveling techniques during product manufacturing. A domestic raw material production line has extensively used 347H as the main shell material for its core equipment, resulting in a high proportion of cracks appearing at the longitudinal and circumferential seams of the shell, severely impacting product production. Summary of the Invention

[0003] The purpose of this invention is to solve the problems of large-diameter, thick-walled 347H type pressure vessels under high temperature and high Cl- content. - To address the phenomenon of cracking during operation in certain environments, a novel longitudinal and circumferential seam bevel design for the shell was developed. This reduces weld stress, decreases the constraint of stainless steel welds, minimizes weld deformation, and significantly improves the weld's resistance to high temperatures and Cl-. - Capabilities that minimize stress corrosion cracking are used for beveling and welding methods for longitudinal and circumferential seams of large-diameter containers.

[0004] The above objectives are achieved through the following technical solutions:

[0005] A bevel for longitudinal and circumferential seams of large-diameter containers, the bevel being a double-sided U-shaped bevel welded to the inner and outer sides of the container, with a bevel gap between the two U-shaped bevels, and a groove being machined inside the container body and welded in the groove.

[0006] The U-shaped bevel has an unequal thickness structure on both sides, with the depth of the deep U-shaped bevel being 0.6-0.7 times the thickness of the container wall.

[0007] The bevel used for the longitudinal and circumferential seams of large-diameter containers has a groove depth of 3-3.5mm.

[0008] The bevels used for longitudinal and circumferential seams of large-diameter containers have a bevel gap of 4-5mm between the U-shaped bevels on both sides.

[0009] A welding method for beveling longitudinal and circumferential seams of large-diameter containers, the method comprising the following steps:

[0010] (1) Process the U-shaped bevels on both sides to make the gap between the two bevels 4-5mm. By widening the gap, the fusion effect of stainless steel at the root of the weld is improved. The bevel blunt edge p is 2-3mm.

[0011] (2) The bevel angle α on both sides is greater than the bevel angle of ordinary low alloy steel, and the bevel width should not be less than the bevel depth on that side.

[0012] W≥2Rcosα+2tanα[T1-R(1-sinα)]+b, the same applies to the shallow U side;

[0013] (3) A groove of full weld length, width L and depth K is machined inside the container body, i.e. on the side in contact with the corrosive medium, for overlay welding of nickel-based alloys with stronger resistance to stress corrosion.

[0014] (4) The two sides of the groove should be machined or ground into a 3 / 5 arc shape with a radius of r to facilitate the deposition of the weld overlay at both ends. The size of r is 3-3.5mm. The groove depth K is also 3-3.5mm. The groove width L should be calculated in advance according to the welding method. The two sides H should be larger than the heat-affected zone range on both sides of the shallow U weld.

[0015] (5) Weld the U-shaped bevels on both sides. During the welding process, the deep U side should be welded first, and the welding should be carried out in the order of deep U-shallow U-deep U to offset the welding deformation in the optimal welding sequence.

[0016] (6) For the surfacing in the groove, use nickel-based welding strips with specifications of 0.5×30mm to surface the center part of the groove. Each pass is 32-33mm wide, with a pass length of 4-5mm and a surfacing height of 3.3-3.7mm. Surface surfacing 2-3 passes in the center position, and use argon arc welding or shielded metal arc welding to surface and fill the sides.

[0017] (7) After the groove is welded, the area outside the dotted line of the inner bevel is removed by mechanical processing or grinding with a special grinding wheel, or only the manual welding parts on both sides are processed.

[0018] Beneficial effects:

[0019] 1. This invention employs U-shaped longitudinal and circumferential weld bevels to reduce weld stress, decrease the constraint of stainless steel welds, reduce weld deformation, and significantly improve the weld's resistance to high temperatures and Cl. - This capability minimizes the formation of stress corrosion cracks.

[0020] 2. The bevel of this invention is a double-sided bevel, with both the inner and outer sides being U-shaped. The purpose of designing it as a double U-bevel is to allow alternating welding on both sides of the bevel during the welding process, so as to maximize the offset of welding deformation caused by the high linear expansion coefficient of austenitic stainless steel.

[0021] 3. The bevel angle α on both sides of this invention should be greater than that of ordinary low-alloy steel, and the bevel width should not be less than the bevel depth on that side. Taking the deep U side as an example, W≥2Rcosα+2tanα[T1-R(1-sinα)]+b, and the same applies to the shallow U side. A smaller bevel depth-to-width ratio is more conducive to the fusion of the weld metal of 347H type stainless steel and to the formation of stainless steel welds with high molten pool viscosity. In addition, it can also reduce the restraint in the root region of the weld and reduce the risk of defects. The root radius R is preferably R8-R10, which is conducive to the fusion of stainless steel submerged arc welding at the appropriate position. Attached image description:

[0022] Appendix Figure 1 This is a schematic diagram of the structure of the present invention;

[0023] Appendix Figure 2 This is a schematic diagram of the groove inside the bevel after welding. Detailed implementation method:

[0024] Example 1:

[0025] A bevel for longitudinal and circumferential seams of large-diameter containers, the bevel being a double-sided U-shaped bevel welded to the inner and outer sides of the container, with a bevel gap between the two U-shaped bevels, and a groove being machined inside the container body and welded in the groove.

[0026] The U-shaped bevel has an unequal thickness structure on both sides, with the depth of the deep U-shaped bevel being 0.6-0.7 times the thickness of the container wall.

[0027] Example 2:

[0028] According to Example 1, the groove depth for the bevel used for the longitudinal and circumferential seams of large-diameter containers is 3-3.5 mm.

[0029] Example 3:

[0030] According to Embodiment 1 or 2, the bevel for longitudinal and circumferential seams of large-diameter containers has a bevel gap of 4-5mm between the U-shaped bevels on both sides.

[0031] Example 4:

[0032] A welding method for beveling longitudinal and circumferential seams of large-diameter containers, the method comprising the following steps:

[0033] (1) Process the U-shaped bevels on both sides to make the gap between the two bevels 4-5mm. By widening the gap, the fusion effect of stainless steel at the root of the weld is improved. The bevel blunt edge p is 2-3mm.

[0034] (2) The bevel angle α on both sides is greater than the bevel angle of ordinary low alloy steel, and the bevel width should not be less than the bevel depth on that side.

[0035] W≥2Rcosα+2tanα[T1-R(1-sinα)]+b, the same applies to the shallow U side;

[0036] (3) A groove with a full weld length, width L and depth K is machined inside the container body, on the side in contact with the corrosive medium, for overlay welding of nickel-based alloys (INCONEL 600 or INCONEL 800, etc.) with stronger resistance to stress corrosion.

[0037] (4) The two sides of the groove should be machined or ground into a 3 / 5 arc shape with a radius of r to facilitate the deposition of the weld overlay at both ends. The size of r is 3-3.5mm. The groove depth K is also 3-3.5mm. The groove width L should be calculated in advance according to the welding method. The H on both sides should first be greater than the heat-affected zone on both sides of the shallow U weld. Secondly, the weld width brought about by the welding method should still be considered to maximize the automatic welding and reduce the amount of manual welding.

[0038] (5) Weld the U-shaped bevels on both sides. During the welding process, the deep U side should be welded first, and the welding should be carried out in the order of deep U-shallow U-deep U to offset the welding deformation in the optimal welding sequence.

[0039] (6) For the surfacing in the groove, use nickel-based welding strips with specifications of 0.5×30mm to surface the center part of the groove. Each pass is 32-33mm wide, with a pass length of 4-5mm and a surfacing height of 3.3-3.7mm. Surface surfacing 2-3 passes in the center position, and use argon arc welding or shielded metal arc welding to surface and fill the sides.

[0040] (7) After the groove is welded, remove the area outside the dotted line of the inner bevel by means of mechanical processing or grinding with a special grinding wheel, or only process the manually welded parts on both sides. Be sure to avoid defects such as undercut, which may cause local Cl during operation. - Excessive concentration can accelerate corrosion.

[0041] Comparative experiment:

[0042] A certain raw material production line has largely replaced INCONEL 800 with 347H as the main material for its core equipment. More than ten such machines in China are already in operation, and through-cracks have appeared in the longitudinal and circumferential seams of the cylinder, directly affecting the production line's progress and causing economic losses.

[0043] The reliability of this bevel was verified through theoretical analysis and process tests:

[0044] On the one hand, the high-temperature resistance and corrosion resistance of the nickel-based isolation layer are superior to those of 347H grade austenitic stainless steel. Using only the weld overlay area with a nickel-based alloy can significantly reduce usage costs. On the other hand, the bonding strength between the nickel-based weld overlay and the 347H substrate was verified through a transverse bending test. The test results show that the INCONEL 600 nickel-based weld overlay has high bonding strength with the 347H substrate, and no defects were found in the weld overlay and fusion line after the bending test. The hardness of the weld overlay and its heat-affected zone is consistent with the overall 347H base material; microscopic metallographic analysis shows no adverse structures; finally, secondary processing of the weld overlay ensures its seamless integration with the substrate without causing any adverse effects.

Claims

1. A welding method for beveling longitudinal and circumferential seams of large-diameter 347H class containers, characterized in that: The bevel is a double-sided U-shaped bevel located on the inner and outer sides of the container. A bevel gap is left between the two U-shaped bevels. A groove is machined inside the container body and welded in the groove. The U-shaped bevel has a structure with unequal thickness on both sides, and the depth of the deep U-shaped bevel side is 0.6-0.7 times the thickness of the container wall; The method includes the following steps: (1) Process the U-shaped bevels on both sides to make the gap between the two bevels 4-5mm. By widening the gap, the fusion effect of stainless steel at the root of the weld is improved. The bevel blunt edge p is 2-3mm. (2) The bevel angle α on both sides is greater than the bevel angle of ordinary low alloy steel, and the bevel width should not be less than the bevel depth on that side. W≥2Rcosα+2tanα[T1-R(1-sinα)]+b, the same applies to the shallow U side; (3) A groove with a full weld length, width L and depth K is machined inside the container body, i.e. on the side in contact with the corrosive medium, for overlay welding of nickel-based alloys with stronger resistance to stress corrosion. (4) The two sides of the groove should be machined or ground into a 3 / 5 arc shape with a radius of r to facilitate the deposition of the weld overlay at both ends. The size of r is 3-3.5mm. The groove depth K is also 3-3.5mm. The groove width L should be calculated in advance according to the welding method. The two sides H should be larger than the heat-affected zone range on both sides of the shallow U weld. (5) Weld the U-shaped bevels on both sides. During the welding process, the deep U side should be welded first, and the welding should be carried out in the order of deep U-shallow U-deep U to offset the welding deformation in the optimal welding sequence. (6) For the surfacing in the groove, use nickel-based welding strips with specifications of 0.5×30mm to surface the center part of the groove. Each pass is 32-33mm wide, with a pass length of 4-5mm and a surfacing height of 3.3-3.7mm. Surface surfacing 2-3 passes in the center position, and use argon arc welding or shielded metal arc welding to surface and fill the sides. (7) After the groove is welded, the area outside the dotted line of the inner bevel is removed by mechanical processing or grinding with a special grinding wheel, or only the manually welded parts on both sides are processed.

2. The welding method for beveling longitudinal and circumferential seams of large-diameter 347H class containers according to claim 1, characterized in that: The groove depth is 3-3.5mm.

3. The welding method for beveling longitudinal and circumferential seams of large-diameter 347H class containers according to claim 2, characterized in that: A 4-5mm gap is left between the U-shaped bevels on both sides.

Images