The classification principle of weld quality of steel structure can be summarized as: Grade I when under tension, grade II when under compression, and grade III for the rest. Its classification requirements are based on the code for welding of steel structures, followed by the design requirements of steel structure engineering.For the inspection of weld quality, self inspection and supervision can be carried out. The following items should be paid attention to in practical inspection. 　　

 1、 For the welding seam made by steel structure processing plant, the percentage should be calculated according to each welding seam. If the percentage is calculated by the number of welding seams, this method is not correct.  

2、 For the welding seam of steel structure installation site, attention should be paid to prevent only checking the lower part but not the upper part; or only checking the easy inspection parts of climbing, not going to the easily inspected parts of climbing, only checking some flat welding, horizontal welding and vertical welding seams, neglecting the overhead welding, dead angle and other difficult parts, the inspection results are difficult to be representative. 　　

 3、 For grade I and II welds, in fact, there is no big difference in welding process and weld quality requirements. The difference between the two is mainly due to the difference in detection proportion, and according to the thickness of steel plate to be inspected, there is only a slight difference in defect parameters and quantity quantification during inspection.  

 4、 Although the fillet weld belongs to the third grade weld in most cases, when there are special requirements in some projects, the design will be improved to no less than grade II or even grade I.Such as the T-shaped connection weld between the rectangular pipe and the rectangular pipe, the rigid joint weld between the I-beam and the lateral embedded parts, the fillet weld grade of the cross beam joint plate and chord on the railway and highway steel bridges, etc.　　

 5、 Some steel structure projects are very tight in terms of construction period and construction arrangement, which will lead to the components that have just been welded in the morning, and are in urgent need of hoisting in the afternoon. This operation is also wrong. The correct way is that for class I and II steel components, the inspection should be carried out 24 hours after welding.  

For steel structure weld quality and inspection classification requirements, in addition to referring to relevant specifications, we should also carefully analyze the “general description of steel structure design” and relevant requirements of the project. If there is any contradiction or unclear, we should communicate with the designer through the owner as soon as possible.