Automatic multi-layer multi-pass welding joint of inner hole of heat exchange pipe

Abstract

This utility model discloses a multi-layer, multi-pass welding joint for automatic welding of the inner bore of a heat exchanger tube, including a tube sheet and heat exchanger tubes. The tube inlet of the tube sheet is machined with a stepped profile, including a reserved inner bevel and a reserved straight edge. The connection end of the heat exchanger tube is correspondingly machined with a limiting step, an inner bevel of the heat exchanger tube, and a straight edge of the heat exchanger tube. The limiting step and the reserved straight edge cooperate, and the reserved inner bevel and the inner bevel of the heat exchanger tube form a V-shaped weld bead with a straight edge, forming three welding layers at the V-shaped weld bead with a straight edge. The straight edge wall thickness, step height, and other parameters of this utility model have been experimentally verified to balance strength and weld penetration. The three-layer, multi-pass welding sequentially solves the problems of root penetration, bevel filling, and sealing reinforcement. Zero-gap structure: completely eliminates the risk of crevice corrosion; stress optimization: reduces triaxial stress in the butt joint and improves resistance to stress corrosion; convenient inspection: the V-shaped bevel with a straight edge allows for clear identification of weld defects by radiographic inspection; adaptable to multi-pass welding path planning of the inner bore welding torch.

Description

Technical Field

[0001] This utility model relates to the field of heat exchanger manufacturing technology, and in particular to a multi-layer, multi-pass welding joint suitable for automatic welding of the inner bore of small-diameter heat exchange tubes. Background Technology

[0002] In shell-and-tube heat exchangers, the connection methods between heat exchange tubes and tube sheets include strength expansion joints, strength welding, a combination of expansion and welding, and internal hole welding. For small-diameter heat exchange tubes (typically Φ≤25mm), internal hole welding with filler wire cannot be implemented due to space constraints, and traditional connection methods have significant drawbacks.

[0003] 1. Fillet welds are under triaxial stress, resulting in low fatigue life;

[0004] 2. Plastic deformation during expansion joints leads to residual stress, which in turn triggers stress corrosion.

[0005] 3. Scale and crevice corrosion easily form in the gap between the pipe and the bore;

[0006] 4. The internal quality of the weld cannot be detected by X-ray or ultrasonic testing. Utility Model Content

[0007] To solve the above-mentioned technical problems, this utility model designs a multi-layer, multi-pass welding joint for automatic welding of the inner hole of heat exchange tubes, which fundamentally eliminates the risk of corrosion and improves the reliability of detection.

[0008] The present invention adopts the following technical solution:

[0009] A multi-layer, multi-pass welded joint for automatic welding of the inner bore of a heat exchanger tube includes a tube sheet and a heat exchanger tube. The tube sheet has a stepped profile at the tube inlet, which includes a reserved inner bevel and a reserved straight edge. The heat exchanger tube connection end is correspondingly machined with a limiting step, an inner bevel, and a straight edge. The limiting step and the reserved straight edge are matched, and the reserved inner bevel and the inner bevel of the heat exchanger tube form a V-shaped weld bead with a straight edge. Three welding layers are formed at the V-shaped weld bead with a straight edge.

[0010] Preferably, the inner diameter of the reserved straight edge is equal to the outer diameter of the straight edge of the heat exchange tube plus a 0.5mm assembly gap.

[0011] Preferably, the outer diameter of the limiting step is equal to the inner diameter of the reserved straight edge.

[0012] Preferably, the reserved inner bevel and the inner bevel of the heat exchange tube are combined to form a 60° V-shaped weld bead with straight edges.

[0013] Preferably, the length of the reserved straight edge is 2mm.

[0014] Preferably, the length of the straight side of the heat exchange tube is 1.8 mm.

[0015] Preferably, the first welding layer of the three welding layers is a self-fluxing welding layer, the second welding layer is a filler welding layer, and the third welding layer is a cover welding layer.

[0016] Preferably, the self-fusion weld layer is welded without filler wire, and the weld depth needs to penetrate the overlap area of ​​the reserved straight edge and the straight edge of the heat exchange tube.

[0017] Preferably, the wire feed in the filler weld layer fills 70% of the bevel volume.

[0018] Preferably, the cover weld layer fills the bevel and forms a rounded corner transition.

[0019] The beneficial effects of this utility model are: (1) The parameters such as the straight edge wall thickness and step height of this utility model have been verified by test to balance the strength and welding penetration. The three-layer multi-pass welding solves the root penetration, bevel filling and sealing strengthening problems in turn; (2) Zero gap structure: completely eliminates the risk of gap corrosion; (3) Stress optimization: reduces the triaxial stress of the butt joint and improves the stress corrosion resistance; (4) Convenient inspection: the V-shaped straight edge bevel makes the X-ray inspection able to clearly identify weld defects; (5) Automation compatibility: adapts to the multi-pass welding path planning of the inner hole welding gun. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the structure of this utility model;

[0021] Figure 2 This is an exploded structural diagram of the present invention;

[0022] Figure 3 This is a schematic diagram of the welding layers of this utility model;

[0023] In the diagram: 1. Tube sheet, 2. Tube hole, 3. Reserved inner bevel, 4. Reserved straight edge, 5. Heat exchange tube, 6. Limiting step, 7. Inner bevel of heat exchange tube, 8. Straight edge of heat exchange tube, 9. First welding layer, 10. Second welding layer, 11. Third welding layer. Detailed Implementation

[0024] The technical solution of this utility model will be further described in detail below through specific embodiments and with reference to the accompanying drawings:

[0025] Example: Figures 1-2As shown, a multi-layer, multi-pass welding joint for automatic welding of the inner hole of a heat exchanger tube includes a tube sheet 1 and a heat exchanger tube 5. The tube hole 2 of the tube sheet is machined with a stepped profile at the inlet. The stepped profile includes a reserved inner bevel 3 and a reserved straight edge 4. The heat exchanger tube connection end is correspondingly machined with a limiting step 6, a heat exchanger tube inner bevel 7 and a heat exchanger tube straight edge 8. The limiting step and the reserved straight edge cooperate with each other. The reserved inner bevel and the heat exchanger tube inner bevel form a V-shaped weld bead with a straight edge. Three welding layers are formed at the V-shaped weld bead with a straight edge.

[0026] The inner diameter of the reserved straight edge = the outer diameter of the heat exchanger tube's straight edge + 0.5mm assembly clearance. The outer diameter of the limiting step = the inner diameter of the reserved straight edge. The reserved inner bevel and the inner bevel of the heat exchanger tube combine to form a 60° V-shaped weld bead with a straight edge.

[0027] The length of the reserved straight edge is 2mm. The length of the straight edge of the heat exchange tube is 1.8mm.

[0028] like Figure 3 As shown, in the three-layer welding system, the first welding layer 9 is a self-fusion welding layer, the second welding layer 10 is a filler welding layer, and the third welding layer 11 is a capping welding layer. The self-fusion welding layer is performed without filler wire, and the penetration depth must penetrate the overlap area of ​​the reserved straight edge and the straight edge of the heat exchange tube. In the filler welding layer, the wire filler fills 70% of the bevel volume. The capping welding layer fills the bevel and forms a rounded transition.

[0029] When using the multi-layer, multi-pass welding joint with automatic welding of the inner bore of the heat exchanger tube, the heat exchanger tube 5 is inserted into the tube hole 2, and the limiting step 6 is tightly fitted with the reserved straight edge 4; the inner bore welding torch is inserted into the tube to perform automatic welding. First, self-fusion welding without filler wire is performed, and the penetration depth needs to penetrate the straight edge lap area. Then, wire is fed to fill 70% of the bevel volume, and finally, the cover weld fills the bevel and forms a rounded transition.

[0030] The embodiments described above are merely preferred solutions of this utility model and are not intended to limit this utility model in any way. Other variations and modifications are possible without departing from the technical solutions described in the claims.

Claims

1. A multi-layer multi-pass welded joint of automatic welding of the inner hole of a heat exchange tube, comprising a tube sheet and a heat exchange tube, characterized in that, The tube inlet of the tube sheet is machined with a stepped profile, which includes a reserved inner bevel and a reserved straight edge. The heat exchange tube connection end is correspondingly machined with a limiting step, an inner bevel of the heat exchange tube, and a straight edge of the heat exchange tube. The limiting step and the reserved straight edge are matched, and the reserved inner bevel and the inner bevel of the heat exchange tube form a V-shaped weld bead with a straight edge. Three welding layers are formed at the V-shaped weld bead with a straight edge.

2. The multi-layer multi-pass welded joint of claim 1, wherein, The inner diameter of the reserved straight edge = the outer diameter of the straight edge of the heat exchange tube + 0.5mm assembly gap.

3. The multi-layer multi-pass welded joint of claim 1, wherein, The outer diameter of the limiting step is equal to the inner diameter of the reserved straight edge.

4. The multi-layer multi-pass welded joint of claim 1, wherein, The reserved inner bevel and the inner bevel of the heat exchange tube are combined to form a 60° V-shaped weld bead with straight edges.

5. The multi-layer multi-pass welded joint of claim 1, wherein, The length of the reserved straight edge is 2mm.

6. The multi-layer multi-pass welded joint of claim 1, wherein, The length of the straight side of the heat exchange tube is 1.8 mm.

7. The multi-layer multi-pass welded joint of claim 1, wherein, The first welding layer of the three welding layers is a self-fusion welding layer, the second welding layer is a filler welding layer, and the third welding layer is a cover welding layer.

8. The multi-layer multi-pass welded joint of claim 7, wherein, The self-fusion welded layer is welded without filler wire, and the penetration depth must penetrate the overlap area of ​​the reserved straight edge and the straight edge of the heat exchange tube.

9. The multi-layer multi-pass welded joint of claim 7, wherein, The filler weld layer contains 70% of the bevel volume filled by the wire feed.

10. The multi-layer multi-pass welded joint of claim 7, wherein, The cover weld layer fills the bevel and forms a rounded transition.

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