until considerable experience has been gained. Such cracks appear as a blur with one side of heavy density fading out
toward the other edge. Since cracks frequently do not extend to the surface, they may not be found by visual inspection
of outside areas. Cracks normal or nearly normal to the line of radiation cannot be seen.
Lack Of Root Penetration.
This will appear on the radiograph as a straight wide line through the center of the weld.
Lack Of Root Bead.
Frequently penetration will barely have been completed or will be lacking very slightly of complete penetration and no
root bead will have been formed. In such instances the radiograph will show total absence of the root bead as indicated
by the superimposed band, but will not reveal the line mentioned above for lack of penetration.
Lack Of Fusion.
Lack of fusion will appear as a blur similar to the angular crack but will have considerably more definition. Frequently
this condition will exist in connection with lack of penetration. In such instances the line mentioned above will have a
blurred edge on one or both sides. The extent of this blur will indicate the depth of the unfused area. Since this blur is
a horizontal projection of an angular plane, the depth of the unfused area will be several times as great as the width of
Incomplete penetration may occur in a fillet weld. This will show on a radiograph as dark lines along one side of weld
This will appear on the radiographs a relatively large round or oblong area in the root area. Where such an area is
indicated merely by a circle with possibly a light area in the center the second pass has filled the original defect. When
this appears as a dark area, the radiographer can be sure that a void of some magnitude exists. Frequently an area will
appear only slightly darker than the weld density, but will contain a very black line in the center. This indicates that
the second pass filled the original hole in the root pass but that a shrinkage crack has developed at this point. Such
shrinkage cracks may extend entirely through the second pass. These are potential stress points. The following Figure
6-45 shows radiographic examples of welds.