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To know the procedures used to perform etch tests and the results derived from the test.
The etch test consists of cutting a specimen
transverse to the weld axis, applying an etching
solution and inspecting the exposed surface.
This form of destructive testing is an excellent
method of determining the soundness of weld
metal and the metallurgical structure produced
by the weld.
The test outlines or defines the weld structure
in relation to the base metal. The etched
surface provides a contrast between the weld,
heat affected zone and base metal. This
form of testing is commonly referred to as
MACROETCH TEST .
The macroetch test is commonly used to
qualify fillet weld procedures and welders.
In this test, the coupon is cut transverse to the
weld axis in one or more locations.
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- Stainless Steelsz“
0 Nickel Alloys:
Acetic and Nitric Acid
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The weld specimens are ground smooth. In
the case of carbon steel, the surface can be
etched with a solution of one part ammonium
persulphate and nine parts water or a solution
of diluted hydrochloric acid.
Safety precautions must be considered when
working with etchants such as hydrochloric
acid. Some acids can cause serious burns
through contact with the skin. The type of
etchant will depend on the metal.
The etchant is normally applied at room
temperature using a cotton swab or similar
applicator. Etching begins the instant the
solution is applied. However, it may be
necessary to continue rubbing the surface until
there is a clear definition of the weld structure.
After the surface is completely etched, it
is washed in clean water and dried. When
handling the specimen, the tester must be
careful not to touch the etched surface. The
etched surface can be preserved by applying
a thin coat of clear lacquer.
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X = Magnification ’
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4* Qualify fillet-welding
- Qualify welders
- Evaluate soundness
- Evaluate penetration
The macrospecimen is inspected by looking
at the etched surface without magnification or
with magnification less than ten X.
The X means the number of times larger the
area appears under a magnifying lens. Ten
X means that the area will appear ten times
larger than normal.
The etched surface is examined to determine
weld soundness. Discontinulties such as
cracks, porosity, incomplete fusion, slag
inclusions and lack of penetration are
The number of weld passes is also visible
, which helps determine where the problems
occur and how the procedure can be modified
to solve them.
Published welding codes provide a standard
of acceptability for evaluation of macroetch
specimens to qualify welding procedures and
The results are recorded on qualification
reports or the quality control documents.
The microspecimen is inspected by examining
the etched surface through a microscope with
a magnification greater than ten X.
-‘ Carbon‘ Steel: .
Nital - 5% Nitric Acid
The microspecimen is prepared similar to
the macrospecimen. _ However the surface is
carefully ground and polished to a mirror—like
finish to remove all scratches. '
A metallographic etching solution is applied to
the surface. Nital solution is commonly used
on carbon steel which consists of 5% nitric
acid in methyl alcohol.
The etched surface is then viewed through a
microscope at high magnifications. Usually
a picture (micrograph) is produced. The
metallurgical structure of the weld metal, fusion
zone and heat affected zone are analyzed for
characteristics such as grain size, carbon
content, and ferrite content.
Few codes requirethis detailed an examination.
However, it is helpful _ln evaluating solutions to
welding problems on ferrous and nonferrous
The microexamination requires a trained
metallographer with skill in metal preparation, '
knowledge of the test procedure and necessary
experience to interpret results.
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1. Explain the difference between macroetch test and microetch test.
2. List the steps required to perform macroetch examination in the proper order in the
Grind macrospecimen _________________________
Apply lacquer *___
Apply etchant to macrospecimen
3. What is the primary use of macroetch testing?
4. What is the primary use of microetch testing?