In winter, the ambient temperature is low. If there are no protective measures for welding steel components, it will have a major impact on the welding quality of steel components.
If welded at low temperature, the steel will be brittle, and the cooling rate of the weld and the heat-affected zone of the base metal will be accelerated, and the hardened structure will be easily produced, and the brittleness will increase. Q345) welding is very harmful.
Therefore, the welding construction in winter must be carried out in strict accordance with the process requirements, and blind welding is not allowed.
Welding Consumables Requirements
1. Strictly manage the welding material warehouse. The welding rod must be dried according to the standard. The number of drying times should not exceed 2, and the exposure time in the air should not exceed 2 hours. If there is no oven on site, you must apply for equipment in time, and arrange special personnel to bake and distribute.
2. The welder holds the heat preservation bucket to receive the welding rod, and the one-time use shall not exceed half a day’s usage; the heat preservation bucket cover must be covered during the welding process, and the heat preservation bucket shall be kept energized; only one rod shall be taken at a time during tack welding; one time shall be taken during welding No more than 3 roots. It is strictly forbidden to expose the welding consumables to damp, and if the welding consumables are found to be damp, they must not be used again.
3. If the welding wire is not used up within four hours, it should be returned to the first-level welding consumable warehouse for storage, and it is not allowed to stay on the wire feeding reel.
4. The purity of carbon dioxide used in gas shielded welding should not be lower than 99.9% (volume ratio), and the water content should not exceed 0.005% (weight ratio).
When using a new bottle of gas, it must be turned upside down for 24 hours and then the valve must be opened to drain the water before use to prevent freezing. When the high pressure of gas in the bottle is lower than 1MPa, stop using it. Before welding, check the indication on the gas pressure gauge, then check the gas flow meter and adjust the gas flow. When in use, the mouth of the bottle must be connected to a heating device.
5. Gas cylinders must be stored in an environment above 0°C. When using bottled gas, stop using it when the gas pressure in the bottle is lower than 1N/mm2. When using below zero, check whether the bottle mouth is blocked by freezing.
General requirements before welding
1. Remove water, scale, rust and oil on the surface of the steel to be welded.
2. The relative humidity in the welding operation area shall not exceed 90%.
3. When the surface of the weldment is wet or covered with ice and snow, heating and dehumidification measures should be taken.
4. Both ends of the main welds of T-joints, cross-shaped joints, fillet joints and butt joints must be equipped with arc-starting plates and lead-out plates. Similarly, it is forbidden to use materials of other materials as the arc strike plate and lead-out plate.
5. The lead-out length of the weld seam for manual arc welding and gas shielded arc welding should be greater than 25mm. The width of the arc starting plate and lead-out plate should be greater than 50mm, the length should be 1.5 times the thickness of the plate and not less than 30mm, and the thickness should not be less than 6mm;
The lead-out length of the non-manual arc welding seam should be greater than 80mm. The width of the arc starting plate and lead-out plate should be greater than 80mm, the length should be twice the thickness of the plate and not less than 100mm, and the thickness should not be less than 10mm.
6. After the welding is completed, use flame cutting to remove the arc starting plate and lead-out plate, and grind them to make them smooth. Do not use a hammer to drop the arc strike plate and lead-out plate.
Welding measures in winter (welding ambient temperature below minus 5°C)
1. Set up the shelter:
In outdoor construction, when the ambient temperature is lower than -5°C, a protective shed must be set up in the welding area to increase the welding ambient temperature and prevent wind and rain.
2. Preheating before welding:
The weld seam should be preheated before welding, and the preheating area should be on both sides of the welding groove. If necessary, the accompanying preheating method should be used to ensure the preheating temperature and interlayer temperature.
The heating temperature is 80-150°C, and the preheating range is 1.5t on each side of the weld (t is the plate thickness), and not less than 100mm.
A far-infrared thermometer is used for temperature measurement, and the temperature measurement point is 75mm from the edge of the groove, on two straight lines parallel to the center of the weld.
2.1. Weld preheating temperature
Note: The preheating temperature of Q345GJ refers to Q345; the preheating temperature of Q390 and 420 refers to Q460; when the plate thickness t=100~110mm, the minimum preheating temperature of Q420, Q460 and steel castings is 180℃.
2.2. The preheating temperature of tack welding is 30~50 degrees higher than that of formal weld.
Welding speed and bead layout
The welding speed of manual arc welding flat, horizontal, and overhead welding is to specify the length of the weld seam welded by each electrode; gas shielded welding is not allowed to swing in a single-pass weld seam, and the thickness of the welding layer is controlled at 5-6mm. The welding rod (torch) and the workpiece clamp The angle is not less than 30°. Allowable maximum swing width during vertical welding: 15mm ~ 20mm.
Slow cooling after welding
After the welding of thick steel plates below zero temperature is completed, measures should be taken to keep warm and cool within the range of 2-3 times the thickness of the plates on both sides of the weld, and the weld should be cooled slowly. The cooling rate should not exceed 10°C/min.
6 Special welding requirements for Q460 steel
6.1 The welding of Q460E steel shall be performed by welders who have passed the welding examination.
6.2Q460E steel shall not be welded below 0°C. If it must be welded, a heat preservation shed must be set up to ensure that the ambient temperature in the heat preservation shed is above 0°C.