various tests that has to be conducted for finding igc and scc

1. TESTS FOR SUSCEPTIBILITY OF
INTERGRANULAR CORROSION
AND STRESS CORROSION
CRACKING
Presented by
Nikhil Koshy Jacob
Industrial Metallurgy
14MY33

2. CONTENTS
Intergranular corrosion
Oxalic Etch Test
Streicher test
Huey test
Strauss test
Stress Corrosion Cracking
Constant stress test
Fracture mechanics test
Slow strain rate test

3. Intergranular Corrosion
It refers to preferential corrosion along the grain
boundaries in corrosive media
It results in loss of strength and ductility
The attack is common in stainless steel , Ni and Al
alloys

4. Tests for Intergranular Stress
Corrosion
The different tests that we use are
Oxalic Etch Test
Streicher test
Huey test
Strauss test

5. Oxalic Etch Test
The oxalic acid etch test is a rapid method of screening
those specimens of certain stainless steel grades. The
test is used for acceptance but not rejection of material
In an environment of 10% H2C2O4 an anodic current of
1A is applied for 1.5 minutes at room temperature to a
polished sample.
By microscopic analysis it is determined if the
specimen needs to undergo further testing or if it is not
sensitized.
If the grain boundaries appear as ditches in , it indicates
that the sample needs further testing.

6. Test setup

7. Streicher test
This test is based on weight loss determinations and
provides a quantitative measure of the relative
performance of the material evaluated.
The procedure includes subjecting a specimen to a 120
hour boil in 2.5% ferric sulfate - 50% sulfuric acid. This
procedure measures the susceptibility of stainless steels
and nickel alloys to inter granular attack
Streicher testing is carried out on samples from finished
tubes in the as-delivered condition or on material that has
been sensitized.

8. Huey Test
The specimens are boiled for five periods, each of 48
hours, in a 65 per cent solution of nitric acid.
The corrosion rate during each boiling period is
calculated from the decrease in the weight of the
specimens.
Properly interpreted, the results can reveal whether or
not the steel has been heat-treated in the correct manner.
The Huey test environment is strongly oxidizing, and, is
only used as a check on whether the material has been
correctly heat treated.

9. Test setup

10. Strauss test
The Strauss test is a standard practice for detecting the
susceptibility of austenitic stainless steels to Intergranular attack.
In Strauss test procedure, the samples are boiled in a solution of
6% copper sulphate and 16 % sulphuric acid
The test time is 24 hours and the evaluation consists of a visual
examination for cracks originating from intergranular corrosion
attacks.
The samples are usually bent before examination. If cracks are
suspected to arise from poor ductility, even in unsensitized
samples, a similar but unexposed sample should be used for
reference.
This test is based on a visual examination of the bent specimen.

11. Stress Corrosion Cracking
Failure of metal resulting from joint action of
◦ Stress
◦ Chemical attack
Initiation and propagation of cracks without
any outside evidence of corrosion
Sudden and unpredictable failure:
Catastrophic

12. Stress corrosion cracking in stainless steel

13. Tests for Stress Corrosion Cracking
Constant stress test
Fracture mechanics test
Slow strain rate test

14. Constant stress test
Constant stress or constant displacement tests essentially
describe a specimen and a loading method that stresses
the specimen while exposed to the solution.
The susceptibility to SCC is then assessed by the time
taken for failure of the specimen, or the development of
cracks in the surface of the specimen.
A common constant displacement test use a U-shaped
specimen, produced by bending a flat plate, and then
stressed by drawing the arms of the U together with a
loading bolt (known as a U-bend test).

15. Fracture mechanics test
Fracture mechanics tests use a specimen with a pre
existing crack.
The tests may be evaluated simply by recording the time
to failure, but it is more common to measure the change
in length of the crack with time, and thereby derive a
graph of crack growth rate as a function of stress

16. Slow strain rate test
The slow strain rate test, or, more accurately, the
constant extension rate test, applies a slow rate of
extension to a specimen.
This ensures that there is a continuing plastic strain at
the surface of the specimen, and encourages the
initiation and growth of stress corrosion cracks.
The result of the test is evaluated in terms of the time
taken for failure to occur, or the appearance of the
fracture surface.
The slow strain test is normally applied to smooth
tensile specimens, although pre-cracked samples may
also be used

17. Reference
Zaki Ahmad, Principles of corrosion
engineering and corrosion control, Sept
2006, Elsevier science and technology
books.
www.tcreng.com