The main defects of welded seam appearance of welded pipe

The main defects of welded seam appearance of welded pipe

Submerged arc welding is a welding method in which an arc burns under a layer of flux. Submerged arc welded pipe mainly includes straight seam submerged arc welded pipe (LSAW) and spiral submerged arc welded pipe (SSAW).

1. Undercut
The reason why unilateral undercut defects are prone to appear during the welding process of welded pipes is that the gap between the forming seams changes too much, there are small burrs or small gaps on the edge of the strip, and the forming is improper. Incorrect. In this case, no major adjustments are required, and the strip edges can be machined as smooth as possible, maintaining a stable form as conditions permit. For the smooth treatment of the edge of the strip, the edge milling machine can be used instead of the disc trimming to solve the problem.
During the welding process of the submerged arc welded pipe, a single undercut will also appear on both sides. The main reasons for this situation are uneven wire diameters, rough wire joints, uneven wire hardness, uneven wire feeding, and instantaneous short circuit of the nozzle caused by metal burrs. Precautions that can be taken in this situation include: Check the diameter of the welding wire. If the contact tip is a prototype contact tip, the diameter of the contact tip should be appropriately increased. The welding wire manufacturer is required to grind the welding wire joints to ensure that the diameter and hardness of the joints are consistent. Pay attention to the trimming and milling of the board to ensure that there are no burrs, regularly empty the internal flux and perform magnetic separation.

2. Weld reinforcement is too high
Reasons for excessive weld reinforcement are:
(1) Improper matching of welding specifications, excessive current, low voltage, and slow welding speed;
(2) The reclining angle of the welding wire is too large, causing the molten pool metal to recede violently;
(3) The distance between the front and back of the welding wire is too small. The wire sticks out too much.
Prevention and control measures include:
(1) Determine reasonable welding specification matching through process test;
(2) The thick-walled steel pipe is welded by slotting, the extension length of the welding wire is reduced, the spacing of the welding wire is appropriately increased, and the eccentricity of the solder joint is appropriately increased.

3. Welding pitting and "herringbone" pattern
The causes of weld pitting and "herringbone" lines are:
(1) The oxidizing atmosphere under welding conditions is too high, that is, the base metal and welding materials contain more oil, rust, and oxidized powder, and the carbon monoxide has too many pores to precipitate, resulting in a large number of pores and surface pitting;
(2) The specificity of the flux is high, the viscosity of the slag is high, the accumulation rate of the flux is high, or the particle size of the flux is too small, so that the bubble pressure between the metal and the slag is greatly increased and pitting occurs.
Prevention and control measures:
(1) Select sintering flux with light specific gravity and low viscosity, ensure that the flux is dry and clean before use, and reduce the accumulation height of flux as much as possible under the premise of unknown arc during use;
(2) Thoroughly remove oil stains, rust and moisture on the surface of weldments and welding wires.

4. Welding bias current
Improper position of solder joints, too large or too small solder joint eccentricity or too fast welding speed, incorrect flux feeding position, asymmetric pressure of flux on molten pool, and excessive arc voltage will cause welding deflection.
Its prevention and control measures mainly include:
(1) Reasonably select the position of the solder joint according to the size of the pipe diameter and the welding specification, so that the molten pool is as close to the horizontal position as possible to complete the crystallization process;
(2) Transport the flux in the correct way to reduce the impact of the flux on the molten pool during the transport process. The flux bowl is best made into a shape with a large top and a small bottom to minimize flux flow in the front of the molten pool in the flux bowl
(3) Adjust the appropriate arc voltage

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