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Gas Tungsten Arc Welding Handbook
the weldment has been in service. This comparison
can help engineers identify areas of the weldment that
are stressed by service.
Destructive Tests
Destructive tests are used for welder qualifi cation
and certifi cation, as well as welding procedure qualifi -
cations. In large production runs, destructive tests are
often made by pulling apart sample units. It is often
less expensive to scrap a part to make a destructive
quality test than to test the parts using more expen-
sive nondestructive tests.
Bend Test
Bend tests are used to determine internal weld
quality. As shown in Figure 18-12, there are three
different types of bend tests:
• face bend (face of the weld is tested)
• root bend (root of the weld is tested)
• side bend (sides of the weld are tested)
In bend tests, a weldment is sliced into test strips,
called coupons. The weld is then bent around a die of a
specifi c size, creating a horseshoe of the coupon. This
process stretches the weld to test the weld’s integrity.
Figure 18-13 shows a radius bend testing machine.
This machine bends the prepared test coupon into a
U form over a specifi ed radius, which is dependent
on the thickness and strength of the material. After
bending, the outer surface and the inner surface of
the U are checked for cracks and other indications as
required by the weld inspection criteria. The outer
face of the bend may be examined by a visual, pene-
trant, or magnetic particle test to detect defects such as
cracks, lack of fusion, and lack of penetration.
Tensile Test
Tensile tests are used to compare the weldment
to the base metal mechanical values and specifi cation
requirements. The weldment is sliced into coupons,
and then each end of the coupon is pulled in opposite
directions until the coupon fails (breaks). A tensile
test machine is shown in Figure 18-14.
Tensile tests are made to determine the following:
• Ultimate strength of the weld. This is the
point at which the weld fails under tension.
• Yield strength of the weld. This is the point
at which the weld yields or stretches under
tension and will not return to its original
dimensions.
• Elongation. This is the amount of stretch that
occurs during the tensile test. It is measured by
placing gauge marks on the sample or coupon
before testing and comparing the after-break
distance with the original gauge marks.
Root bend
Male
die
Female die
Face bend Side bend
Figure 18-12. The three types of bend tests are shown
here. The root bend test places the greatest amount of
stress on the weld root. The face bend test places the
greatest amount of stress on the weld face. The side bend
places the greatest amount of stress along the weld axis.
Completed
test samples
Figure 18-13. A radius bend testing machine. (Mark Prosser)