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Common defects and solutions of pipeline welding

Views : 2426
Author : PARIS-Terry Ding
Update time : 2020-08-31 16:11:37
There are many kinds of welding defects, which can be divided into external defects and internal defects according to their position in the weld. External defects are also called appearance defects.
The external defects are located on the surface of the weld, which can be observed by naked eye or macroscope.
The internal defects are located in the inner part of the weld, which must be detected by destructive inspection or special non-destructive testing method

As shown in Fig. a b , the weld shape is uneven, the weld bead width is uneven, the weld reinforcement is too large or too small, the weld width is too wide or too narrow, and the transition between the weld and the base metal is not smooth.

Cause analysis
(1) The angle, width and assembly clearance of weld groove are not uniform.
(2) Improper selection of electrode diameter results in too high filling layer, loss of groove contour line, different cover width, too high weld seam and coarse ripple.
(3) The quality of back gouging and gouging is poor, and the weld bead width is different.
(4) The welding current is too large or too small, the welding method and angle are improper, and the welding speed is uneven.

2. Harmfulness
If the size of the weld is too small, the strength of the welded joint will be reduced; if the size of the weld is too large, it will not only waste the welding materials, but also increase the deformation of the welding structure. If the transition between weld metal and base metal is not smooth and sharp angle appears, it will cause stress concentration and reduce the bearing capacity of welded structure.
preventive measure

(1) Use automatic and semi-automatic cutting machine or planer to process groove.
(2) The welding seam assembly clearance should be controlled within the value required by the standard specification. After the back side is cleaned by carbon arc air gouging, the groove and carbonization layer are trimmed with grinding wheel to make the groove width consistent.
(3) Select appropriate welding current and electrode diameter, abide by welding process, master operation technology skillfully, and keep welding speed uniform; manual welding operators should master the speed and angle of welding rod skillfully to obtain beautiful weld.
5. Treatment method
If the weld reinforcement is too high, the grinding wheel shall be used for dressing. If the width is different or the height is not enough, repair welding shall be carried out again, and the welding joint shall be smooth.
 
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