1、 Preparation before installation and welding of steel structure

The test steel includes q345gjc-z15 (wall thickness of 70 mm), q345gjc-z15 (wall thickness of 40 mm), Q345 C (flange thickness of 28 mm), and the welding positions are column to column transverse welding, column to beam flat welding (including truss beam upper and lower flange flat welding), and T-shaped angle vertical welding.Groove form and size shall be in accordance with design requirements.Mechanical and physical tests were carried out after the appearance and ultrasonic inspection were qualified.

The test results show that the tensile strength of the joint reaches the standard value of the tensile strength of the base metal, and the joint bends 180 ° without cracks.The adopted welding materials and technical conditions of welding equipment shall meet the national standards with excellent performance.Slag cleaning, air gouging, electrode drying and heat preservation devices shall be complete and effective.

2、 Materials and equipment for manual arc welding and CO2 gas shielded welding

(1) The welding rod shall be dried in a high-temperature drying box, and the drying times of welding rod shall not exceed twice.

(2) The packaging of welding wire shall be in good condition. If the welding wire is damaged and causes pollution, bending or disorder, part of it shall be discarded.

(3) The purity of CO2 gas shall not be less than 99.9% (volume ratio), the water content shall be less than 0.05% (weight ratio), and the use shall be stopped when the high pressure in the bottle is less than 1MPa.

(4) The voltage of the welding machine shall be normal, the ground wire shall be firmly pressed, the contact shall be reliable, the cable and welding tongs shall not be damaged, the wire feeder shall be able to feed the wire evenly, and the air pipe shall be free of air leakage or blockage.

3、 Installation welding procedure and general regulations

The general welding sequence is: inspection before welding → preheating and derusting → installation and welding of base plate and arc strike plate → welding → inspection 

　　1Before welding, check the groove angle, blunt edge, gap and stagger amount, and remove the rust spot, oil stain and oxide scale in the groove and on both sides.

　　2. warm up.Before welding, use gas welding or special baking gun to evenly heat the base metal within 100mm of the groove and both sides, and use surface thermometer to measure the temperature to prevent the temperature from not meeting the requirements or local oxidation of the surface, preheating temperature.

　　3. recheck the preheating temperature. If the temperature is not enough, reheat it to make it meet the requirements.

　　4. for the installation and welding of base plate and arc strike plate, the surface cleanliness requirements are the same as that of the groove surface, the base plate and base metal shall be close, and the arc strike plate and base metal shall be firmly welded.

　　5. welding: the weld bead of the first layer shall seal the connection between the base metal and the base plate in the groove, and then weld layer by layer to fill the groove. After each weld is welded, the welding slag and spatter must be removed, and the welding defects shall be timely removed and repaired.

　　6. an interface must be continuously welded. If it is necessary to stop welding in the middle of the process, heat preservation and slow cooling treatment shall be carried out. Before re welding, heating shall be carried out again as required.

　　7.In case of rain or snow, the welding shall be stopped. There shall be a wind and rain shed around and above the component welded junction. When the wind speed is greater than 5m / s, the welding shall be stopped.When the ambient temperature is lower than zero, preheating and post heating measures shall be taken according to the regulations.

　　8. the carbon structural steel shall be subject to the weld flaw detection inspection 24 hours after the weld is cooled to the ambient temperature and the low alloy structural steel is completed.

　　9. welders and inspectors shall carefully fill in the operation record form.