280
Gas Tungsten Arc Welding Handbook
been located by a radiographic test, the defect can be
marked on the X-ray fi lm. The fi lm is aligned over the
weld, and a punch can be used to indent the area over
the defect. The next step is to determine the depth of
the defect from the top and root surface using ultra-
sonic testing. Routing or grinding is done from the
surface nearest to the defect.
Finding the defect in the weld by grinding or
routing requires both skill and patience. Porosity and
large areas exhibiting lack of fusion are generally easy
to locate and remove. Cracks and small areas with
incomplete fusion are more diffi cult to locate.
The following is a suggested procedure for
repairing an internal defect in a groove weld:
1. If the defect depth is known, remove metal to
within approximately 1/16″ (1.6 mm) from the
defect. During the metal-removal process, use a
magnifying glass to inspect the ground area. If
the crack is in the right plane, a light blue surface
will sometimes be found at the edge of the crack.
This is caused by overheating of the crack edge.
This is also a good situation for a dye penetrant
test.
2. Perform a penetrant test on the grooved area. If
no indication of a crack or defect is seen, remove
the penetrant.
3. Grind .010″–.015″ (.25 mm–.38 mm) deeper.
4. Penetrant test the grooved area again. Continue
penetrant testing, grinding, and retesting until
the defect is found.
5. If the defect is still not found, X-ray to determine
if the defect remains.
If the crack is not found after removing metal
halfway through the part, reweld the ground area.
Then work from the opposite surface to remove the
crack.
Never grind a slot or a hole through the part. Repairing
a slot causes excessive distortion in the adjacent areas
or shrinkage and the possibility of more defects.
The removal of defects in fi llet welds is diffi cult due
to limited access of the grinder. If the penetrant is
allowed to penetrate into the joint, it can cause many
problems during weld repair. For a fi llet weld, it is
easier to use visual inspection or radiographic tests to
ensure that the defect has been removed.
Preparing for Repair
After the defect is removed, prepare the area for
welding by removing all rough edges on the ground
area. Any oil, grease, scale, or penetrant residue must
be removed with alcohol or acetone. Do not use grit
blasting in the grooved area. Grit material can become
embedded in the ground area and become trapped in
the weld repair.
Welding for Repairs
• If possible, use stringer beads with minimum
amperage for minimum shrinkage of the
joint.
• Whenever possible, use a current-tapering
(crater fi ll) control on amperage to prevent
crater cracks.
• Clean scale and oxides from each weld pass.
• Visually inspect each weld pass after
cleaning.
• If the weld repair is deep, have an X-ray
made after two or three completed passes to
confi rm that new cracks have not formed.
This should also be done if there is any
doubt about removal of the original crack.
• Always use a backing gas if the root of the
weld may be exposed to air.
• Where possible, use the original parameters
for preheat, interpass temperature, and
postheat.
• Do not build the repair crown any higher
than is required. Each pass that is made
stresses the base of the weld due to
shrinkage.
• When the grain size must be controlled
throughout the repair, weld temper beads on
top of the weld, as shown in Figure 18-33.
These beads reduce the surface grain size
and are removed after welding.
Temper bead height (Remove after welding)
Normal crown height
Figure 18-33. Temper beads are used to obtain an even
structure throughout the top area of the weld. Since
they add signifi cant height to the crown, they are usually
removed after welding.