The picture below shows why a weld with a high depth to width ratio or
concave throat MAY be more subject to cracking upon cooling. Joint restraint,
heat input, root opening, and other factors may change the results. This is
usually not a problem on thinner materials. Submerged arc welding can sometime
have this problem more often than other processes.
The concave weld profile is not a problem and is often desirable on the root
pass of GTAW welded joints provided the thickness of the weld is not too great.
Flare bevel or flare groove welds can sometimes have problems associated with
bead profile.
Sometimes a line or crease appearing in the face of
a root is an indicator of complete fusion with the root. This would usually be a
single vee or single bevel groove joint welded from one side only. In highly
restrained joints, this crease or line becomes a crack.

Since 23 Mar 04