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Keyword pre-assembly, bus welding
0 Brief
In order to produce and carry a large number of reinforced concrete bridge piers of Donghai Bridge, Shanghai Haoli Hoisting Machinery Co., Ltd. built a gantry crane with working level A5, lifting capacity 350t, span 36m, lifting height 19m and self-weight 644t. Install it on the site of Shenjiawan Island on the East China Sea. The machine has two box-shaped main beams with a net length of 41.3m, the height is more than 4m, the width is 2m, the web thickness is 16mm, the upper flange plate and the lower flange plate are both 24mm thick, and there is a compartment type rib in the middle. The ribs, as well as the longitudinal reinforcement angles (see Figure 1), are all Q235B, each weighing 238t.
1 Segmentation of the main beam
The main beam was pre-assembled into two in the factory in Shanghai, reaching the accuracy shown in Table 1. It will be transported from the factory to the Lu Chaogang terminal, then shipped to the Shenjiawan terminal, and finally transported to the use site. Considering the convenience of transportation, each main beam is made in three sections, then assembled and welded into two parts on the use site; finally, the same end beam is assembled, welded, and lifted to the outriggers, and the whole gantry crane is added. Installation and commissioning. The Shanghai Welding Association conducted a consultation on the whole process of the assembly of the main beam at the site, from the formulation to the specific implementation.
Table 1 Accuracy of the main beam after pre-assembly
Project standard (mm) actual (mm)
Left beam and right beam
Upper arch ≥ 50 73.5 75
Horizontal bending 20 16 14
The local flatness of the web is within H 11. 2 9 9.5
The remaining 19.2 15 14
Upper flange plate horizontal deflection 10 6.3 6.3
Web vertical deflection 20 11 13
The butt joint of the upper flange plate of the segmented portion and the butt joint of the web, the butt joint of the web and the butt joint of the lower flange plate are staggered by 300 mm (see Fig. 2).
2 Assembly of the main assembly of the main beam
The main beam section is placed on the reinforced concrete block with a height of 1.2 m, and the whole main beam is assembled by means of a jack and an angel gourd to achieve the accuracy listed in Table 2.
Table 2 Accuracy of assembly of main beam site assembly
Item Target (mm) Actual (mm)
Left beam and right beam
Upper arch ≥ 50 73.5 75
Horizontal bending 20 15 13
The local flatness of the web is within H 11. 2 9 9
The remaining 19.2 15 15
Upper flange plate horizontal deflection 10 6.5 6.5
Web deflection 20 11 13
Connector height difference ≤1 1 1
Joint clearance ≤ 2 1.5 2
Dislocation between the outside of the joint ≤1 0.6 0.8
3 web butt welding
3.1 The web is docked using the groove shown in Figure 3.
3.2 The webs on both sides are synchronized, in the same direction (from bottom to top), and the same parameters are used for vertical welding. The appropriate parts of the groove and its sides are polished before welding.
3.3 First weld the two weld beads on the inside with φ4 welding rod (Fig. 4).
3.4 Then remove the root with a φ10 carbon planing strip on the outside (Fig. 5), then polish it with an angled grinding wheel, and confirm that there are no welding defects by MT flaw detection.
3.5 Finally, another 3 weld beads are vertically welded on the outside with φ4 welding rod (Fig. 6).
4 Butt welding of the lower flange plate
4.1 After polishing the bevel and its sides, first weld the two weld beads with φ4 welding rod (see Figures 7 and 8).
4.2 Then remove the root with φ10 carbon rod on the upper part (Fig. 9), then polish it with a grinding wheel, and confirm that there is no defect by MT flaw detection.
4.3 Finally, the remaining 4 weld beads are flat welded with φ4 and φ5 welding rods (Fig. 10).
4.4 Butt welding of the lower flange plate, no matter the overhead welding or flat welding, the welding method is adopted.
5 Butt welding of the upper flange plate [butt welding with the lower flange plate, see (1) ~ (4) and Figure 7 ~ 10 of 5].
6 Welding parameters (Table 3)
Table 3 Welding parameters
Welding Method Welding Position Welding Rod Welding Current I(A) Arc Voltage U(V) Welding Power and Polarity
Grade diameter φ (mm)
Manual welding flat welding E4315 (J427) 4 140-160 20-22 DC, RP
5 180-200
Vertical welding 4 130-150
Overhead welding 4 120-140
7 electrode baking
Baking temperature: 300-350 ° C; baking time: 2 h.
8 welding environment
8.1 The welding site emphasizes the construction of temporary work sheds to avoid wind and rain.
8.2 The site is located in the island, the air humidity is high, so before welding, it is emphasized to carefully remove the oil, rust, water and dirt within 30mm of the groove and its sides, that is, to remove the oil stain, remove the rust spots, and bake off the water. Trace and remove dirt.
9 weld appearance inspection results
9.1 Weld seam height ≤ 3mm.
9.2 The width of the weld is approximately equal to the width of the upper mouth of the groove + (4-6) mm.
9.3 No unfilled.
9.4 Undercut depth ≤ 0.5mm, cumulative length of undercut ≤ 10% weld length.
9.5 no welding.
9.6 No surface pores, surface slag, surface cracks.
9.7 Splashes have been scraped.
9.8 No arc scratches.
10 NDT
The requirements for nondestructive testing and their results are listed in Table 4.
Table 4 NDT requirements and results
The flaw detection type of the flaw detection area is tested by the standard qualified grade.
Butt weld (focus on cross weld) UT 100% GB11345-89 BIII BII, BIII
RT 5% GB3323-87 II I, II
Welded root part MT 100% JB4730-94 qualified
11 weld repair
According to the relevant specifications, the weld is allowed to be repaired twice (more than two times should be studied separately). This has happened during this welding process. The specific practice of repairing is:
11.1 According to the RT result, find the defect part, determine the defect type (the crack is not seen in this welding, only the pore, the slag and the unfused), analyze the cause of the defect (the wind and rain protection measures are improper, the roots are not thorough, the operation If it is not enough, the special rework process documents will be prepared and will be repaired by experienced welders.
11.2 Plan the defect with a carbon planer, polish it with a grinding wheel, and grind the bottom and both ends into an arc shape.
11.3 Use small welding line energy, namely fine electrode, small current, short arc (low voltage), fastness (the electrode does not swing laterally), DC welding power supply and polarity welding; the first welding current Slightly larger.
11.4 Polish the surface of the weld to make it smooth transition to the surrounding weld.
11.5 Rework RT after cooling the weld to be repaired.
12 Welding deformation control
12.1 For each joint of the main beam, the web is strictly synchronized on the two sides (same side or the same side) in the same direction, in the same direction, and the same parameters are applied, thereby reducing the side curve and distortion of the main beam.
12.2 Between the lower flange plate and the upper flange plate, it is strictly necessary to weld the flange plate first and then weld the flange plate to ensure the upper arch of the main beam.
12.3 For each butt weld of the lower flange plate (or the upper flange plate), the upper weld of the lower weld is first welded, and the upper weld of the upper weld is welded, which is also beneficial for ensuring the upper arch of the main beam. .
The measurement results of post-weld deformation are shown in Table 5.
Table 5 Measurement results of the main beam assembly after welding
Item Target (mm) Actual (mm)
Left beam and right beam
Upper arch ≥ 50 70 71
Horizontal bending 20 17 16
The local flatness of the web is within H 11. 2 9.5 10
The remaining 19.2 16 15
Upper flange plate is tilted horizontally 10 6.5 7
Web vertical deflection 20 12 13.5
Connector height difference ≤1 1 1
Dislocation between the outside of the joint ≤1 0.6 0.8
13 welding wage quality
Special emphasis is placed on the fact that welders are certified on a case-by-case basis.
14 Conclusion
As a major technical measure of the Donghai Bridge, the crane has completed the final assembly and was delivered for use in the summer of 2003 after commissioning.
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