I. Conditions for welding operations
1.Operating personnel
There are two types of welding operators: equipment operators and welders. The former must undergo professional technical training and obtain relevant qualification certificates before performing steel pipe welding operations, while the latter must pass relevant technical inspections and obtain professional certificates before being employed. Safety protection equipment must be prepared during construction to ensure the safety of construction personnel.
2.Operating tools
After the personnel are ready, they need the assistance of material conditions. This includes drawings, grinders, wire brushes, lifting equipment, anti-blocking agents, flat shovels, weld gauges, etc.
II. Steps of welding operations
Preliminary preparation
(1) Understand the requirements of the drawings and ensure the quality of the tool parts.
(2) Repeatedly check whether the overall specifications of the assembled steel pipe joints or components meet the requirements of the drawings, and whether the welding materials and welding grooves meet the quality requirements of the drawings and process standards.
(3) Check whether the equipment, tools and power supply required for the operation are complete.
(4) Pay attention to the environment of the welding area:
① Ambient temperature: When the working environment temperature is -10°C < x < 0°C, the base metal within a range greater than or equal to twice the thickness of the steel plate and not less than 100mm in all directions of the assembled joint welding area should be heated to above 20°C before construction. When the temperature is lower than -10°C, welding operations are not advisable. Construction can only be carried out strictly in accordance with the construction plan after formulating a special plan that can ensure the welding quality.
② The ambient humidity should be greater than 90%.
Implementation process
(1) Use lifting equipment to lift the components onto the tool rack and make the welding points in the flat welding position as much as possible. For positions with few welds, horizontal welding and vertical welding can be used for connection.
(2) Check the oil stains, rust, moisture and other sundries within 20mm of the component welding area.
(3) Select welding materials according to the engineering welding process requirements and adjust the welding parameters.
(4) Before welding, carry out corresponding preheating according to the welded material and ambient temperature.
(5) The main structure welds with a thickness greater than 40mm and materials of Q235 and above.
(6) When the welding environment temperature is lower than 0°C and not lower than -10°C, the base metal of the welding area of the assembled joint should be heated to 20°C, which is greater than or equal to twice the welding temperature. The thickness of the steel plate is not less than 100mm. Welding can be carried out after the above steps; when the minimum preheating temperature of the base metal is higher than 20°C, a higher preheating temperature should be used for preheating.
(7) When welding the square rectangular pipe sections to the diaphragm, the welding sequence must be strictly controlled. The welding of the arc transition section can adopt the vertical upward welding position, and the starting and ending positions of the arc transition section should extend a certain distance to both sides. When welding the joints, vertical and horizontal welding can also be used for the joints.
(8) Strictly abide by the welding process regulations of specific projects during the welding process and control the temperature between passes to reduce welding stress and deformation. Measures such as "C" clamps can be used for overall assembly welding to reduce welding deformation. During the welding process, it is necessary to continuously observe the welding status and weld quality and make timely adjustments in case of any abnormalities. The thickness of each weld should not be greater than 5mm, and the width of each weld should not be greater than 15mm. When a single-pass weld cannot meet the requirements of the weld size, multi-layer and multi-pass welding is required, and the interlayer temperature must be strictly controlled. The interlayer temperature should not be lower than the minimum preheating temperature or higher than 230°C.
(9) After the part welding is completed, use a flat shovel and a grinder to process the burrs, welding slag and poor welds on the surface of the steel parts. If there are any defects, they should be repaired. After the welds are completely cooled and meet the non-destructive testing conditions, non-destructive testing should be carried out on the full penetration welds. If there are excessive defects detected, air carbon arc gouging or a grinder can be used to remove the defects and carry out repair welding.
