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Non-destructive and Destructive Testing
Figure 6.12 Macro sample
the test surface and the support of the test piece during the
test.
Macro samples
Macro tests (Fig. 6.12) are used to check the internal weld
quality of a welded test coupon and so are used in welder
performance qualification tests (welder approval tests). A
section is removed from the test coupon and then the surface
to be inspected is made smooth and polished by lapping to a
finish of approximately 600 grit before etching it with ‘nital’
(a mixture of around 10% nitric acid in industrial alcohol).
The mixture will depend on the material being tested.
The macro specimen is then inspected at a magnification of
5– 10 for welder-induced imperfections such as porosity,
slag inclusions, cracks, lack of fusion etc. It is common for
the macro to be taken at a stop/start location (particularly in
the root runs) as this is where defects are most likely to be
found. Obviously any stop/starts in root or hot passes would
have to be marked on the sample by an inspector before
subsequent runs obscured them.
The sample should also be inspected when it is first
removed to check for any imperfections which may then be
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Woodhead Publishing Ltd – A Quick Guide to Welding and Weld Inspection
Data Standards Ltd, Frome, Somerset – 17/9/200906QG Welding chap6.3d Page 83 of 87