ASTM G1 :- Preparing, Cleaning, and Evaluating Corrosion Test Specimens

This practice covers suggested procedures for preparing
bare, solid metal specimens for tests, for removing corrosion
products after the test has been completed, and for evaluating
the corrosion damage that has occurred.

 Significance and Use

The procedures given are designed to remove corrosion
products without significant removal of base metal. This allows
an accurate determination of the mass loss of the metal or alloy
that occurred during exposure to the corrosive environment.

Reagents and Materials

Purity of Reagents—Reagent grade chemicals shall be
used in all tests. Unless otherwise indicated, it is intended that
all reagents conform to the specifications of the Committee on
Analytical Reagents of the American Chemical Society where such specifications are available.4 Other grades may be used,
provided it is first ascertained that the reagent is of sufficiently
high purity to permit its use without lessening the accuracy of
the determination.

Purity of Water—Unless otherwise indicated, references
to water shall be understood to mean reagent water as defined
by Type IV of Specification D1193

 Methods for Preparing Specimens for Test

•  For laboratory corrosion tests that simulate exposure to
  service environments, a commercial surface, closely resembling the one that would be used in service, will yield the most
  meaningful results
• It is desirable to mark specimens used in corrosion tests
  with a unique designation during preparation. Several techniques may be used depending on the type of specimen and
  test.
• Stencil or Stamp—Most metallic specimens may be
  marked by stenciling, that is, imprinting the designation code
  into the metal surface using hardened steel stencil stamps hit
  with a hammer. The resulting imprint will be visible even after
  substantial corrosion has occurred. However, this procedure
  introduces localized strained regions and the possibility of
  superficial iron contamination in the marked area.
• Electric engraving by means of a vibratory marking
  tool may be used when the extent of corrosion damage is
  known to be small. However, this approach to marking is much
  more susceptible to having the marks lost as a result of
  corrosion damage during testing.
• Edge notching is especially applicable when extensive
  corrosion and accumulation of corrosion products is anticipated. Long term atmospheric tests and sea water immersion
  tests on steel alloys are examples where this approach is
  applicable. It is necessary to develop a code system when using
  edge notches.
• Drilled holes may also be used to identify specimens
  when extensive metal loss, accumulation of corrosion products,
  or heavy scaling is anticipated. Drilled holes may be simpler
  and less costly than edge notching. A code system must be
  developed when using drilled holes. Punched holes should not
  be used as they introduce residual strain
• When it is undesirable to deform the surface of
  specimens after preparation procedures, for example, when
  testing coated surfaces, tags may be used for specimen identi�fication. A metal or plastic wire can be used to attach the tag to
  the specimen and the specimen identification can be stamped
  on the tag. It is important to ensure that neither the tag nor the
  wire will corrode or degrade in the test environment. It is also
  important to be sure that there are no galvanic interactions
  between the tag, wire, and specimen.

 Methods for Cleaning After Testing

1. Corrosion product removal procedures can be divided
   into three general categories: mechanical, chemical, and electrolytic
2. An ideal procedure should remove only corrosion
   products and not result in removal of any base metal. To
   determine the mass loss of the base metal when removing
   corrosion products, replicate uncorroded control specimens
   should be cleaned by the same procedure being used on the test
   specimen. By weighing the control specimen before and after
   cleaning, the extent of metal loss resulting from cleaning can
   be utilized to correct the corrosion mass loss.
3. The cleaning procedure should be repeated on specimens several times. The mass loss should be determined after
   each cleaning by weighing the specimen.