Page 99 - Quick Guide to Welding and Weld Inspection by S.E. Hughes, Clifford Matthews
P. 99

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

                                   83


               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
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