Welded steel tube is seamed steel pipe, also known as welded pipe. Its production is the process of bending the tube blank (steel plate and steel strip) into a tube with the required cross-sectional shape and size by various forming methods, and then welding the welds together by different welding methods to obtain a steel tube. Compared with seamless steel pipe and welded pipe, it has the characteristics of high product precision, especially wall thickness precision, simple main equipment, small footprint, continuous operation in production, flexible production, and wide product range of the unit. Welded steel pipe has simple production process, high production efficiency, many varieties and specifications, and less equipment investment, but its general strength is lower than that of seamless steel pipe.
Welding procedure specification requirements and welding inspection
1. Welder qualification
Welders must undergo specialized training in basic theory and operational skills, pass the examination and obtain a welder qualification certificate for grid steel pipe structures.
2. Welding materials for welded pipes
The use and management of welding materials shall be carried out in accordance with JB/T 3223.
3. Weld quality grade
(1) The quality grade of welds shall be determined according to the requirements of drawings and design documents. The requirements for weld quality grades are as follows:
a. Circumferential butt welds and welds connecting the hanger plates shall meet the first-class weld quality requirements.
b The weld seam connecting the cross arm and the main pipe shall meet the quality requirements of the secondary weld seam.
c Rigid pipe intersecting welds, lap fillet welds connecting steel pipes and neck flat welded flanges, circumferential fillet welds connecting steel pipes and flat flanges,the longitudinal butt weld of the steel pipe shall meet the appearance quality requirements of the secondary weld.
d Other welds shall meet the quality requirements of Class III welds.
(2) The longitudinal welds of the tower body or the main pipe of the cross-arm should be arranged in the direction outside the diagonal line of the structural section.
4. Welding process requirements
(14) Measures must be taken when the following situations occur in the welding workplace, otherwise welding is prohibited.
a When the wind speed in the welding operation area of electrode arc welding exceeds 8m/s, and the wind speed in the welding operation area of gas shielded arc welding and flux cored wire arc welding exceeds 2m/s; when there is draft or blower in the welding operation area of the production workshop
b The relative humidity is greater than 90%;
c When welding steel pipes of steel grades below Q345, the ambient temperature is lower than -10°C; when welding Q345 steel, the ambient temperature is lower than 0°C; when welding steel grades above Q345, the ambient temperature is lower than 5°C.
(2) The groove type and size of the weld should be designed based on the relevant regulations of GB/T 985.1 and GB/T 985.2, and the groove shape and size of the special requirements of the drawings should be determined according to the drawings and combined with the welding procedure evaluation .
(3) Groove processing should preferably be done by mechanical processing, and can also be prepared by automatic or semi-automatic gas cutting, plasma cutting, or manual cutting. However, it should be ensured that the groove of the weld seam is smooth and free of burrs, and there must be no scale, rust, oil, etc. within 50mm on both sides of the groove, and there must be no defects such as cracks and gas cutting tumors.
