Measures to prevent cold cracks in pipe fittings

The prevention of cold cracks is mainly caused by reducing the diffusion hydrogen content, improving the structure, and reducing the welding stress. Specific measures are:

1.Preheating before welding and slow cooling after welding. This not only improves the metallographic structure of the welded joint, reduces the hardness and brittleness of the heat affected zone, but also accelerates the outward diffusion of hydrogen in the weld and can reduce the welding stress.

2.Choose the right welding specification. If the welding speed is too fast, the quenching structure is easily formed due to the fast cooling rate; if the welding speed is too slow, the heat-affected zone will be widened and the grain will become coarse. Therefore, the welding speed is too fast or too slow, which will promote the generation of cold cracks.

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3.Use reasonable assembly and welding sequence. Reduce the restraint stress of the welded joint and improve the stress state of the weldment.

4.Choose the right welding material. For example, an alkaline low-hydrogen electrode and a submerged arc flux with high alkalinity are used. Dry the electrode and flux before welding, and do it with you. Remove oil, rust and other contaminants from the wire to reduce the diffuse hydrogen content in the weld.

5.Before welding, carefully remove the water, oil, rust and other dirt on the basic metal surface around the groove. To reduce the source of hydrogen.

6.Dehydrogenation should be carried out immediately after welding to allow hydrogen to escape from the welded joint.

7.After welding (especially for easily hardened steel), the stress-relieving annealing treatment should be carried out immediately. This not only reduces or eliminates welding residual stress, but also improves the microstructure and properties of the joint. At the same time, it can also promote the outward diffusion of oxygen in the weld.

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