What are the requirements for non-destructive testing and classification of weld?

According to the importance ofthe structure, load characteristics, weld form, working environmentand stress state, different quality grades shall be selectedaccording to  following principles.

1. In the components requiringfatigue calculation, all butt welds shall be fully welded, and theirquality grades are as follows

The compression grade of buttweld or T-butt fillet weld and weld perpendicular to the weld lengthis grade II and the tensile grade is grade

If the longitudinal force isparallel to the length of the weld, the butt weld shall be class II

2. The butt weld with the samestrength as the base metal shall be fully welded. In the componentsthat do not need to calculate fatigue, its quality grade shall not belower than grade in tension and grade in compression.

3. The T-shaped weld betweenthe web and l flange of the crane beam with large working systemweight and lifting capacity Q ≥ 50t and between the upper chord ofthe crane leg and the gusset plate shall be fully welded. The weld isgenerally a combination of fillet joint and butt joint, and itsquality shall not be lower than grade II.

4. The quality grades offillet welds of "I" joints that do not require fullpenetration or combined welds of butt joints and fillet welds withpartial penetration, as well as fillet welds of lap joints are asfollows:

For structures directlybearing dynamic load and crane beams with crane lifting capacityequal to or greater than 50t, such weld quality standard shall reachgrade II.

Visual inspection is generallyadopted for appearance inspection, and crack inspection shall becarried out with 5x magnifying glass under appropriate lightingconditions. Magnetic particle flaw detection or penetrant flawdetection can be used when necessary, and measuring tools andcalipers shall be used for dimension measurement.

The appearance quality of weld shall meet the following requirements

There shall be no defects suchas incomplete penetration, root shrinkage, undercut and poor joint.The primary and secondary welds shall be free of defects such as slaginclusion, air hole, arc scratch and crack on the surface.