Steel Structure Construction
Preparation before installation and welding of steel structure:
The test steels included Q345GJC-Z15 (wall thickness 70mm), Q345GJC-Z15 (wall thickness 40mm) and Q345C (flange thickness 28mm), and the steel structure construction welding positions are column to column transverse welding, column to beam flat welding (including flat welding of upper and lower flange of truss beam) and T-shaped corner welding. Groove type and size are based on the design requirements. The mechanical and physical tests will be carried out after the weld appearance and ultrasonic inspection are qualified.
Manual arc welding and CO2 gas protection welding materials and equipment:
(1) The electrode shall be dried in the high temperature drying box, and the electrode shall not be dried more than twice.
(2) The packaging of the welding wire should be in good condition. If damaged package leads to contamination, bending and disorder of the welding wire, it should be partially abandoned.
(3) The purity of CO2 gas should be no less than 99.9% (volume ratio), the water content should be less than 0.05% (weight ratio), and the use should be stopped when the pressure in the bottle is lower than 1MPa.
(4) The voltage of the welding machine should be normal, the ground wire is firmly pressed, the contact is reliable, the cable and the welding pliers are intact, the wire feeder should be able to evenly feed the wire, and the gas pipe should be free of leakage or blockage.
Installation welding procedures and general regulations
The general order of welding is as follows: pre-welding inspection → preheating and rust cleaning→ welding pad and arc guide plate → welding → inspection
(1) Before welding, check the groove Angle, blunt edge, crack and unfitness of butt weld, rust spot, oil stain and oxydic iron sheet inside and on both sides of the groove should be cleaned up.
(2) Preheat. Before welding, gas welding or special roasting gun preheat temperature by evenly heating the base material within 100mm on the groove and both sides, and measuring the temperature with a surface thermometer to avoid the temperature doesn’t meet the requirements or local surfaces are oxidized.
(3) Recheck the preheating temperature, If the temperature is not enough, it should be reheated to meet the requirements.
(4) The surface cleaning degree of the welding pad and arc plate is the same as that of the groove surface. The underboarding and the base material should be tight, and the arc plate and the base material should be solidly welded.
(5) Steel structure construction welding: The welding passage of the first layer should seal the connection between the base material and the underboarding in the groove, and then be welded layer by layer to fill the groove. After each weld is finished, welding slag and splash must be removed, and welding defects should be rub out and mend in time.
(6) An interface must be welded continuously. If it is forced to stop welding halfway, it should be treated with thermal insulation and slow cooling. Before welding, it should be reheated according to the regulations.
(7) Steel structure construction welding should be stopped in rainy and snowy days. There should be a wind shield and canopy around and above the welding joint of the component. Welding should be stopped when the wind speed is greater than 5m/s. When the environment temperature is below zero, preheating and post-heating measures should be taken in accordance with the regulations.
(8) Carbon structural steel should be conducted the weld inspection when weld cools to the environment temperature, low alloy structural steel should be conducted after the weld inspection completed 24h .
(9) Welders and inspectors should fill out the job record form carefully.
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