2. Introduction
• Corrosion tests are important as their
application of the test result is important in
corrosion engineering.
• These tests are done in order to select the
material of construction for equipment in the
process industries.
• It is important for the duplicate the actual
plant service conditions.
3. Classsification
• Laboratory tests – small specimens, small vol
solution. screening test to determine material
warrants further investigations.
• Pilot-plant or semiworks tests – test is made in a
small scale plant which duplicates the large plant.
Most desirable test.
• Plant or actual service tests
• Field test
• The last two tests are done when an operating plant
is available. Evaluate the corrosion behaviour of
existing materials as processed conditions change.
4. Purpose of test
• Evaluate and select materials for a specific
environment or a given application.
• Evaluate new or old metals and alloys to
determine the environments in which metals
and alloys are suitable.
• Control of corrosion resistance of materials or
corrosiveness of environment.
• Study the mechanism of corrosion.
5. Steps in corrosion testing
• Materials and specimens- information about the specimen. Size for a
laboratory test is 1/16 to ¼ in thick and 1 in wide and 2 in long. Plant
and field test specimens are of same size or larger.
• Surface preparation-polishing by abrasive cloth or paper, chemical
treatments or passivating pretreatments.
• Measuring and weighing: surface area is calculated.
• Exposure techniques : support the specimen for exposure to
corrosive environment.
• Duration: proper selection of time and number of periods of
exposure.
• Planned interval tests
• Aeration
• Cleaning specimen after exposure: mechanical, chemical, electrolytic
8. • 1st test:
• This is the laboratory equipment for this test.
• The liquid or slurry in glass lined tank is
recirculated and pumped directly into the face
of rotating disk of the specimen.
• The specimen are hung in the tank to know the
btw low and high velocity.
• Dis: open tank not suitable for toxic vapours.
• Box interchangable is used has 2
compartments with orifices in the separating
wall. Jets of fluids will impinge the specimen
9. • 2nd test:
• Closed metal surface in fuming HNO3 ,
• Specimens are hung in a tank, placed in a bracket,
so that return of pipe impinges the specimens
• Here even the pumps, valves, elbows etc can also
act as specimens,
• Even galvanic corrosion can be tested by joining
pipes or flanges of different metals
10. • 3rd test:
• Loop test under closely anticipated actual
operation conditions.
• Lacque centre for corrosion technology in
wrightrsville beach, north carolina does actual sea
water test by pumping it for a long periods
through pipes ,
• Effect of velocity is studied here , it uses a 5 in
disks attached at end of rotating spindles.
• Disks are rotated at a 1140rpm in a wooden tank
and sea water enters , flows through another
pipe.
11. • 5th test :
• Materials technology institute project was to test
the effect of flow rate, geometry, O2conc , pH
• They created 3 systems 1. a flow through a pipe
system, 2. annular flow system, 3. rotating
cylinder system.
• they found that the rotating cylinder system was
more effective, due to its simplicity, compactness,
convenient for testing.
12. Crevice corrosion
• 1st test:
• Gasket materials are held between bolted strips
of type 316 SS. Duplicate gaskets are used, they
are seperated by a third strip btw the 2 outer
strips.
• Tests is evaluated by estimating the percentage
of area attacked, measuring depth of pits,
gasket condition.
13. • 2nd test:
• 2 disks are held together by a bolt and nut of
same mtl .
• Make a tight center joint by tapering, a crevice
is created at the center .
• 3rd test:
• Laying on a horizontal metal specimen a small
pile of sand, slugde or piece of rubber, gasket
mtl. This is placed in corrosive environment.
• 4th test:
• Merely wrapping the specimen with a string,
cord or rubber band.
14. • 5th test :
• Specimen consists of rods containing a male thread
and female thread,
• These are screwed together with gaskets or
without or spacers.
• 6th test:
• Ohio test –the test specimen are prepared as ½ * 4
in strip is bent downwards on a large radius
• The bend causes the tips to spring back slightly
result in a crevice.
15. • 7th test:
• New multiple crevice corrosion test that allows
comparison between alloys
• Two grooved delrin washers are pressed on
each side of specimen with a threaded rod.
• Test offers a probability of crevice attack of
alloys.
16. Intergranular corrosion
• Any corrosion test an be used as a test for
intergranular as specimens are exposed to
localised attack.
• 1st test: Huey test for SS (ASTM-A262)
• Exposure to boiling 65%HNO3 for five 48hrs.
• Sensitized mtl exhibits high corrosion rates.
• Useful to know the CR of mtl .
• Even Maleic acid, lactic acid , CuSO4-H2SO4
acid, FeSO4-H2SO4 , can also be used.
17. • 2nd test: Streicher test for SS
• Oxalic acid screening test (ASTM A-262-55T)
indicates sensitized mtl and reduces by 90% the
number of Huey tests.
• It consists of polishing a small specimen
through No. 000 paper, etch with oxalic acid
10%, for 1.5 min under current density
1A/cm^2, examine under the surface at 250x to
500 x.
• Step structure then properly ht, if it is a ditch
structure then it is intergranular corroded.
18.
19. • 3rd test :
• Type 316L when sensitized for 1hr at 1250C ,it
forms a sigma phase , this phase is high corrosion
rates fails in huey test.
• Warren test is done where 10% HNO3 -3% HF at
70-80C to evaluate 316L.
• It is done for 2hrs or five ½ hrs.
• Then the mtl is severely attacked .
• If ratio cr of sensitized mtl by quench annealed is
less than 1.5 the steel is acceptable.
20. Pitting
• Expose the specimen as large as possible for a
long time as possible
• We measure the max pit depth, no of pits per
unit area , avg depth.
• Max pit depth is very imp.
23. • in the before 2 figures fig.4.9 shows a bracket
and specimen used in Stress corrosion test.
• The fig.4-10 shows an autoclave where the
chloride containing waters are placed in it.
• Condensation from the top the autoclave drip
on the specimen
• This an excellent test for stress corrosion
24. • Specimen are stressed in 2 ways :
• Constant strain , constant load
• Variety of sizes, shapes, method of stressing the
specimen.
• Shape common: u bend or horseshoe type
• Here a bolt is placed through the holes in the
legs of specimen and it is loaded by tightening a
nut or bolt.
• Dis: might be a galvanic corrosion, specimen
should be stress relieved.
25. • Surface stress is calculated of the flat strip
specimen by formula of Eulers:
26. • 2nd test:
• Constant load test:
• Suspended dead weights on specimens with or
without levers pulling longitudinally
• Stresses are high as 50 to 100%Y.S.
• Precracked specimens are also used sometimes
to avoid the time for crack initiation,
28. • 1st method:
• Used to monitor the corrosion under variety of
environment
• Technique is simplified no need of A.E. since
measurements need a few minutes only the
corroding material itself acts as a reference.
• Counter to A.E. need be noble.
• Fabricate the 3 electrodes with same mtl in a
compact test probes screwed into pipelines
29. • 2nd method: reference electrode is removed.
Polarisation is done in both anodic and cathodic
directions.
• Dis: not accurate
• Linear polarisation to be done by measuring no of
data points within 5 mv to max accuracy,
• It should be compared with other corrosion tests.
31. • LCCT does many types of tests housed in a
building including erosion corrosion, corrosion
fatigue, galvanic couple etc.
• Test equipment like pumps on docks, anodes
and other specimens are suspended in sea
water.
• Complete facilities like welding, machining,
equipment , computer, data acquisition
• At Kure beach , atmospheric exposure racks of
80ft to 800ft from the ocean are located nearby
beach, thousands of panels of metals & alloys,
paint metallic coated specimens are exposed for
a certain time or years.
