Control Measures of Weld Reinforcement of Welded Pipe

Weld reinforcement refers to the height of the part of metal on the connecting line between the two welding toes on the weld surface. Generally speaking, reinforcement refers to the part protruding from the base metal surface or the deposited metal above the connecting line at the end of fillet welding (i.e. welding toe).

Advantages and disadvantages of weld reinforcement

Advantages: there should be weld in the welding process, because this layer plays a role of heat preservation and slow cooling, which has a great role in refining grain and reducing welding stress, and it is also the accumulation area of impurities such as pores. Disadvantages: the pressure vessel does not want to have mutation, which leads to local stress concentration. In addition, the reinforcement has defects, which may be the core of fatigue crack, crack source → fatigue propagation The test shows that the service life of the equipment with reinforcement is 2.0-2.5 times shorter than that of the equipment without reinforcement after grinding.

control measures

1. The steel pipe with larger wall thickness should be beveled: for the steel pipe with wall thickness greater than 14.3mm, the X-shaped groove should be beveled and pre welded. If the pre welding condition is not mature, the outer weld should be processed into U-shaped groove before welding by air gouging, grinding wheel automatic grinding or milling.

2. Adjust the welding line energy: check whether the welding line energy is appropriate. Generally, the acid corrosion sample of the welding joint is used to check. One is to check the overlap degree of the internal and external welds, and the other is to check the width of the weld bead waist. The overlap amount is generally greater than 1.5mm, but the overlap amount of the internal and external welds is 1.3 ~ 3.0mm, higher than 3.0mm means that the line energy is large

The larger the welding line energy is, the more welding wires are melted per unit time. For high-strength steel, the welding line energy should be strictly controlled. In order to reduce the line energy of each layer, multi pass welding (more than 2 passes) is generally adopted when welding high-strength steel plate, and the welding line energy should be strictly controlled The shape factor should be within 1.3-2.0 mm.

3. When using multi wire welding, it is better to use thinner front wire: if the diameter of the original external welding three wires is 4mm + 3.2mm + 3.2mm, it is better to change the front wire to Ф 3.2mm, because under the same current, the depth of fusion of the wire with Ф 3.2mm is greater than that of the wire with Ф 4mm, that is to say, the wire with Ф 3.2mm can reach the same level when using the wire with Ф 4mm, even if some line energy is reduced This is because the current density of fine wire is higher than that of thick wire.

Experience has proved that, under the condition of other conditions unchanged, the penetration depth of the front wire with diameter of 3.2mm is about 20% greater than that of the front wire with diameter of 4 mm, which is more obvious when the groove is not opened or the groove is not planed. However, when the welding wall thickness is greater than 14.3mm and the current of the front wire is about 1000 a, the front wire with diameter of 4mm should be used, otherwise the stable combustion of the arc may be affected.

4. Screw welding needs to adjust the position of internal and external welding head: during the internal welding of submerged arc welded pipe, the position of internal welding head should be adjusted to reduce or remove the "saddle" internal weld as far as possible. During the external welding, the spatial position of welding head should also be adjusted to reduce or remove the "fish back" external weld as far as possible. This is mainly realized by adjusting the eccentric center value of the external welding point. Screw welding with different diameters Pipe, the center value of the external welding spot is different, the above introduces the control measures of weld reinforcement of welded pipe, hoping to help you.