Welding related knowledge

1. There shall be no defects such as cracks and weld bead on the surface of the weld. The first and second level welds shall not have defects such as surface pores, slag inclusions, crater cracks, arc scratches, etc. And the first-level welds are not allowed to have defects such as undercuts, incomplete welds, and root shrinkage.

Note: Due to the importance of the primary and secondary welds, there should be specific requirements that are not allowed for surface pores, slag inclusions, crater cracks, and arc abrasions. Defects such as undercuts, incomplete welds, and root shrinkage affect dynamic loading. The impact is great, so the first-level weld must not have such defects.

2. For welds that require pre-welding or post-welding heat treatment, the pre-heating temperature or post-heating temperature should meet the requirements of the current relevant national standards or be determined through process tests. The preheating zone is on both sides of the weld bead, and the width of each side should be more than 1.5 times the thickness of the weldment, and should not be less than 100 mm; the post heat treatment should be carried out immediately after welding, and the holding time should be based on the plate thickness per 25 mm plate. The thickness is determined for 1h.

Note: Welding preheating can reduce the cooling rate of the heat-affected zone and play an important role in preventing the occurrence of delayed welding cracks. Post-weld heat treatment is mainly to dehydrogenate the weld to prevent cold cracks. The timing and timing of post-heat treatment The holding time directly affects the effect of post heat treatment, so it should be carried out immediately after welding, and the treatment time should be appropriately increased according to the plate thickness.

3. The external quality standards of the secondary and tertiary welds shall meet the requirements. The third-level butt weld shall be subject to appearance quality inspection according to the second-level weld standard.

4.The allowable deviation of weld size should meet the requirements

Note: Defects such as under-welded, undercut, arc scratches, etc. are strictly forbidden for the dynamic load structure, and should be restricted to a certain range in the second and third level welds. Outer dimension deviations such as butt weld reinforcement, misalignment, partially penetrated butt and fillet welds, and fillet weld leg size and reinforcement will also affect the load-bearing capacity of steel structures.

5. When a concave fillet weld is welded, there should be a gentle transition between the weld metal and the base metal; the concave fillet weld must not leave a cut mark on its surface.

Sixth, the sense of weld seam should reach: uniform shape, good shape, smooth transition between weld bead and weld bead, weld bead and basic metal, and weld slag and spatter are basically removed.