278
Gas Tungsten Arc Welding Handbook
For all other types of metal, use small rotary
tungsten carbide tools to remove the crack.
Do not use grinding wheels on nonferrous
material. When repairing, add only suffi cient
fi ller metal to match the adjacent weld contour.
• Undercut at the edges of the weld,
Figure 18-28. Dirt, scale, and oxides may be
present in the undercut area. These impurities
can cause further defects if not removed prior
to weld repair. Remove these impurities by
grinding or routing as previously described.
Be careful not to remove base metal adjacent
to the undercut. Since the repair will widen
the original crown size, use lower currents and
suffi cient wire to prevent additional undercuts
and underfi ll.
• Porosity, or pores in the weld, Figure 18-29.
Remove isolated or single pores with a rotary
tool for weld repair. Remove multiple and
linear (aligned in a row) pores by grinding
or machining. Then reinspect the weld by
radiographic or ultrasonic inspection to ensure
that the porosity has been completely removed
before repairs are started. For weld repair,
always fi ll the deepest part of the recessed area
fi rst. Keep each layer of weld level until the
area is fi lled.
• Cold laps, Figure 18-30, are areas of the weld
that have not fused with the base metal. Cold
laps can occur on fi llet welds or butt welds,
usually as a result of a travel speed that is too
slow. Since the extent of the overlap cannot
be determined by NDT, remove the entire
Figure 18-27. A cutting or grinding wheel can be used to
remove cracks from the weld. (Mark Prosser)
Undercut
Undercut
Figure 18-28. Undercut on fl at groove welds can occur
on either edge of the weld. Groove and fi llet welds made
in the horizontal position will usually have undercut on the
upper part of the weld.
Linear
porosity
Scattered
porosity
Fillet weld
Groove weld
Figure 18-29. Isolated pores can occur in any portion of
the weld. Linear (aligned) pores usually are found near the
bottom, along the sidewall, or at weld intersections.