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Gas Tungsten Arc Welding Handbook
into cross sections, which are then polished, etched, and
examined visually or with specialized testing equip-
ment. Cross section tests include the following types:
• Macrotest. Polished sections of the weld are
prepared for viewing with the naked eye
or a magnifying glass (low magnifi cation).
Increased defi nition of the weld layers and
passes can often be obtained by etching the
sample with a suitable etchant.
• Microtest. Very highly polished sections of
the weld are prepared for viewing with high-
power microscopes. This type of test is used to
determine grain size, content, and structure.
• Microhardness test. Very highly polished
sections of the weld are tested on special
machines to determine the hardness of
a very small area. The results can then
be evaluated to determine the hardness
variations within the grain structures and the
weld zones.
Nick-Break Test
Nick-break tests are destructive tests that are
very simple to make. They are used to determine the
internal quality of a weld with regard to porosity, lack
of fusion, and slag. Notches are cut in the sides of a
weld coupon in the weld area. The coupons are then
laid across a support on each end and force is applied
with a hammer to try to break the weld sideways for
a simple internal inspection. A nick or groove cut
into the weld helps the specimen break when force is
applied.
A section of the weld to be tested is removed from
the weld and prepared as shown in Figure 18-17. The
coupon is then placed into a vise, Figure 18-18, and
broken with a sharp blow to the upper section. Defects
can then be observed in the broken areas.
Figure 18-16. The impact test machine arm swings
downward to break the coupon at impact. The results are
shown on the gauge in foot-pounds. (Photo courtesy of
Tinius Olsen)
1/8″ (3.2 mm)
Approximately 1″ (25.4 mm)
Do not remove crown and penetration
Cut slot with hacksaw
or oxyacetylene torch
1/8″ (3.2 mm)
Figure 18-17. Nick-break test dimensions.
Vise
Figure 18-18. Nick-break test setup.