Different quality grades shall be selected according to the importance of the structure, load characteristics, weld form, working environment and stress state, etc., according to the following principles:
1. In the components requiring fatigue calculation, all butt welds should be fully welded, and their quality grade is:
1) For transverse butt welds or t-shaped butt and corner welds where the force is perpendicular to the length direction of the weld, they shall be grade ONE under tension and grade two under compression;
Longitudinal butt welds with 2 forces parallel to the length of the weld shall be secondary.
2. In the component that does not need to calculate fatigue, the butt weld that requires the same strength as the base metal should be welded through, and its quality grade should not be lower than two when it is under tension, and two when it is under pressure.
3. For heavy-class working system and lifting weight Q≥ 50T, the weld of t-shaped joint between the web and L flange of the crane beam and between the upper chord of the crane analysis frame and the joint plate shall be thoroughly welded. The weld form is generally a combination of butt and corner weld, and its quality grade should not be lower than two.
4. Fillet welds or partially penetration butt and fillet combination welds used for "I" joints that do not require penetration, and fillet welds used for lap joints, whose quality grade is:
1) For structures directly bearing dynamic loads and requiring fatigue checking and intermediate working crane beams whose lifting weight is equal to or greater than 50T, the appearance quality standard of welding seams shall conform to grade II;
2) For other structures, the weld appearance quality standard can be grade II.
Visual inspection is generally used for appearance inspection, crack inspection should be supplemented by 5 times magnifying glass and carried out under appropriate lighting conditions, if necessary, magnetic particle inspection or penetration inspection can be used, and dimension measurement should be applied with measuring tools and calipers.