Various cases and analysis of incomplete penetration

July 17, 2019

Various cases and analysis of incomplete penetration

Incomplete penetration refers to defects caused by the fact that the base metal does not melt and the weld metal does not enter the joint. According to the welding method of the welded parts, the roots are not welded and the middle is not welded.

The root is not welded because the liquid weld metal does not enter the blunt edge of the root, and most of it exists in the single-sided welding of the V-shaped or U-shaped groove. The middle is not welded because the liquid metal does not enter the middle blunt edge, and most of it exists in the double V-shaped or double U-shaped groove double-sided welding.

(The weld is not welded to the defect)

The lack of penetration in the weld will reduce its effective area and seriously reduce the mechanical properties such as the strength of the welded parts. Incomplete penetration will also cause stress concentration and severely reduce the fatigue strength of the weld. In addition, when the welded part is under load-bearing stress, it may develop into a crack if it is not welded, and may eventually cause the weld to crack. The incomplete penetration is more harmful than the defects such as pores, slag inclusions and tungsten traps, which are harmful defects. The following two figures show the submerged arc welding seam of the base material thickness of 8-15mm, and the overall gouging weld seam is not welded.

(not welded in the weld)

Causes of incomplete penetration:

1) The welding current is small and the melting depth is shallow;

2) The groove and gap size are unreasonable, and the blunt edge is too large;

3) magnetic biasing effect;

4) The eccentricity of the electrode is too large;

5) Poor cleaning between layers and roots.

Using a larger current for soldering is the basic method to prevent under penetration. In addition, when welding the fillet weld, replace the direct current with alternating current to prevent magnetic partial blow, rationally design the groove and strengthen the cleaning, and use short-arc welding and other measures to effectively prevent the occurrence of incomplete penetration.

Unwelded film image features

(1) The typical image that is not penetrated is a thin straight black line. The contours on both sides of the defect are neat, which is the machining mark of the blunt edge of the groove. The width of the unwelded image is just the width of the gap of the blunt edge.

(the root is not penetrated)

(2) Sometimes the blunt edge of the bevel is partially melted, the outline of the image becomes less tidy, and the width and blackness of the defect image are locally changed. However, as long as it can be judged to be a linear defect at the root of the weld, it is determined to be unwelded. through.

(not welded)

(3) The position of the projection on the base of the weld is not penetrated. Generally, in the middle of the weld, it may be biased to one side due to the reasons of transillumination and welding.

(4) The incomplete penetration is intermittent or continuous, and sometimes it can penetrate the entire negative film.

The following is the actual working radiation detection film image

(not penetrated and rounded defects)

As shown in the above figure, the non-penetration defect has a straight black line in the film and is at the center of the weld, which can be surely determined to be a defect of incomplete penetration.

(not penetrated and rounded defects)

As shown in the above figure, it can be clearly seen from the figure that there are many circular defects (circular vents) in the center of the weld. It can be seen carefully that a black line at the center of the weld connects the circular defects together. The black line is the unpenetrated image.

The information from Another source

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