As the molten pool is located below the weldment, the higher the temperature, the gravity of the molten metal of the electrode will hinder the excessive falling. The larger the volume of the molten pool, the smaller the surface tension of the molten pool, and the molten pool metal will fall under its own gravity. Therefore, during overhead welding, the back of the weld is easy to sag, and there will be weld beading on the front, which is difficult to form a weld bead

We should understand it dialectically, which is mainly reflected in the heating stage and crystallization stage.

Arc striking is the process of igniting and generating stable arc. There are two arc striking methods: direct arc striking method and scratcharc striking method. Directarc striking method: first align the electrode with the part to be welded of the weldment, touch it gently, and then lift the electrode for 2-3mm to ignite.

1、The quantity, type and distribution of non-metallic inclusions are the essential causes of laminar tearing and the origin of the opposite sex and mechanical properties of steel.

Residual stress and deformation after welding generally exist at the same time. In the welding structure of low carbon steel, the influence of welding deformation on the welding structure is generally greater than the welding stress

From the analysis data of welded pipe scrapping, it can be seen that roll adjustment process plays a very important role in welded pipe production. That is, in the production process, if the roll is damaged or seriously worn, part of the roll shall be replaced in time in the unit, or a certain type of welded pipe shall be produced continuously and fully, and the whole set of roll shall be replaced.

Residual stress and deformation after welding generally exist at the same time. In the welding structure of low carbon steel, the influence of welding deformation on the welding structure is generally greater than the welding stress.

Slagremoval. Carefully clean the slag at the included angle of the basemetal and the bottom weld on both sides of the groove, and the slagat the overlap of welding joints.

Incomplete penetration refers to the defect that the base metal is not melted and the weld metal fails to enter the root of the joint. According to the welding method, it can be divided into intermediate incomplete penetration and root incomplete penetration.

In the welding process, if the interlayer temperature is too high,the grain will grow and T8 / 5 will increase. During on-site welding,normalizing treatment cannot be carried out and the original strengthand toughness of the steel will be lost. Therefore, the interlayertemperature must be strictly controlled in the welding process toprevent grain growth.