2. Before welding construction, the construction unit shall prepare the welding procedure documents according to the qualified welding procedure qualification results or the conditions of exemption from welding procedure qualification, and shall include the following contents:
(1) welding method or combination of welding methods;
(2) Specification, brand, thickness and coverage of parent material;
(3) Specification, category and model of filler metal;
(4) Welded joint form, groove form, size and allowable deviation;
(5) welding position;
(6) Type and polarity of welding power supply;
(7) cleaning the roots;
(8) Welding process parameters (welding current, welding voltage, welding speed, welding layer and weld distribution);
(9) Temperature range between preheating temperature and track;
(10) post-welding stress relief treatment process;
(1 1) Other necessary regulations.
Second, the welding operating conditions
3. When welding, the ambient temperature, relative humidity and wind speed in the operation area shall meet the following requirements. When welding needs to exceed this requirement, a special scheme shall be prepared:
(1) The operating environment temperature should not be lower than-10℃;
(2) The relative humidity in the welding operation area should not be greater than 90%;
(3) In manual arc welding and self-shielded flux-cored wire arc welding, the maximum wind speed in the welding operation area should not exceed 8m/s, and in gas shielded welding, the maximum wind speed in the welding operation area should not exceed 2m/s. ..
4. A stable operating platform and protective shed shall be set for on-site high-altitude welding.
5. Before welding, steel wire brushes, grinding wheels and other tools should be used to remove impurities such as scale, rust and oil stains on the surface of the parts to be welded. Weld groove shall be inspected according to the current national standard "Code for Welding of Steel Structures" GB5066 1.
6. Welding operation must be evaluated according to welding process parameters.
7. When the ambient temperature of welding operation is lower than 0℃ and not lower than-10℃, heating or protective measures should be taken. Before welding, the base metal of the welded joint and the welding surface in all directions should be heated to the specified minimum preheating temperature, and not lower than 20℃.
Ⅲ tack welding
8. The thickness of the positioning weld should not be less than 3mm, and should not exceed 2/3 of the design weld thickness; Length should not be less than 40mm and 4. Multiplied by the thickness of the thinner part of the joint; The spacing should be 300 mm ~ 600 mm.
9. The tack weld and the formal weld shall have the same welding process and welding quality requirements. The ends of multi-pass locating welds shall be stepped. For welded joints with steel backing plates, tack welding shall be carried out in the joint groove. The preheating temperature of tack welding should be 20℃~50℃ higher than that of formal welding.
Ⅳ Arc striking plate, lead-out plate and gasket plate
10. When the arc striking plate, lead-out plate and backing plate are made of steel, steel with yield strength not greater than the nominal strength of welded steel shall be selected, and the weldability shall be similar.
1 1. Arc striking plate and lead-out plate shall be set at the weld end. The lead-out length of covered electrode arc welding and gas shielded welding shall be greater than 25mm, and that of submerged arc welding shall be greater than 80mm. After welding is completed and completely cooled, the arc striking plate and the lead-out plate can be removed by flame cutting, carbon arc gouging or mechanical methods, and should be polished and leveled. It is forbidden to knock them down with a hammer.
12, the steel backing plate should be closely connected with the base metal of the joint, and the gap should not be greater than 1.5mm, and should be fully fused with the weld. In manual arc welding and gas shielded arc welding, the thickness of steel backing plate should not be less than 4 mm; When submerged arc welding, the thickness of steel backing plate should not be less than 6 mm; When electroslag welding, the thickness of steel backing plate should not be less than 25mm.
ⅴ preheating and temperature control between tracks
13. The preheating and temperature control between tracks should adopt heating methods such as electric heating, flame heating and infrared heating, and adopt special temperature measuring instruments for measurement. The preheating and heating zone should be located on both sides of the welding groove, and the width should be greater than 1.5 times the thickness of the welding piece and should not be less than 100 mm. When the temperature measuring point is a non-enclosed space component, it should be at least 75mm away from both sides of the welding groove on the back of the heating surface of the welding piece. When it is a closed space component, it should be located at the front side not less than100 mm away from both sides of the welding groove.
14. The preheating temperature and interlayer temperature of welded joints shall comply with the relevant provisions of the current national standard "Code for Welding of Steel Structures" GB5066 1; When the preheating temperature selected by the process is lower than the relevant provisions of the current national standard "Code for Welding of Steel Structures" GB5066 1. It shall be determined by process qualification test.
ⅵ Control of welding deformation
15. The welding process and welding sequence adopted should minimize the deformation and shrinkage of components, and the following welding sequence can be adopted to control the deformation:
(1) Butt joints, T-joints and cross joints shall be symmetrically welded on both sides when the placement conditions of components permit or are easy to overturn; The members with symmetrical sections are symmetrically welded to the neutral axis of the members; Nodes with symmetrical connecting rods shall be symmetrically welded to the joint axis at the same time;
(2) For asymmetric double-sided groove weld, it is advisable to weld a part of the deep groove side first, then fill in the shallow groove side, and finally complete the deep groove side weld. For ultra-thick plates, it is advisable to increase the number of cycles of symmetrical welding in turn;
(3) For the long weld, sectional back welding, skip welding or multi-person symmetrical welding should be adopted;
16, when welding components, reserved welding shrinkage allowance or preset anti-deformation method should be adopted to control shrinkage deformation, and shrinkage allowance and anti-deformation value should be determined by calculation or experiment.
17. When assembling welded components, the joints with large shrinkage should be welded first, and then the joints with small shrinkage should be welded, and the joints should be welded under less constraints.
ⅶ stress relief after welding
18, when there is a requirement for stress relief after butt welding in design documents or contract documents, butt joints or joints or components with dense welds in the structure that need to be checked for fatigue should be annealed locally by electric heater and integrally by heating furnace. When the structural size is only stable, vibration method can be used to eliminate stress.
19. the post-weld heat treatment shall comply with the relevant provisions of the current industry standard "post-weld heat treatment method for welded components of carbon steel and low alloy steel" JB/T6046. When the electric heater is used for local stress relief heat treatment of welded components, it shall meet the following requirements:
(1) heating equipment equipped with automatic temperature controller shall be used, and its heating, temperature measurement and temperature control performance shall meet the use requirements;
(2) The width of the heating plate (belt) on both sides of the component weld should be at least 3. The thickness of the steel plate, and not less than 200mm；;
(3) Except for the heating plate (belt), both sides of components shall be covered with heat insulation materials.
20. When hammering to eliminate the stress of the intermediate welding layer, a round-headed hand hammer or a small vibration tool should be used, and the base metal of the root weld, the cover weld or the weld groove edge should not be hammered.
2 1. When the vibration method is used to relieve stress, the selection of process parameters and technical requirements of vibration aging should comply with the relevant provisions of the current industry standard "Selection of process parameters and technical requirements for vibration aging of welded components" JB/T 10375.
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