Types of Wall Wash Test (WWT)
Hydrocarbon (HC)/Water Miscibility Test
1. For making a standard or reference solution: Add 10ml
of the laboratory grade methanol and 90ml of Deionised
water(D.I. Water) laboratory grade in a sample/nessler
tube.
2. To make a test solution: Add 10 ml of the tank sample
and 90 ml of Deionised water (D.I. Water) laboratory
grade in a sample/nessler tube.
Note: Adding more methanol to DI water makes the
hydrocarbon test progressively stricter. The dilution ratio
depends on the company and load ports. Other commonly used
ratios include (25:75, 33:67, and 50:50)
1. Shake or Invert the nessler tube once or twice to mix the
D.I. water and methanol.
2. Now leave the sample/nessler tube and wait for 20
minutes.
3. Place the tube on a black surface and switch off the
lights. Use a penlight to shine through the side of the
tubes while looking down through the liquid column.
4. If a bluish tint is observed, it indicates slight
hydrocarbons are present. If a whitish haze is observed,
this usually indicates moderate to heavy hydrocarbons
are present.
5. If the sample is clear, this means no hydrocarbons are
present.
6. To check for specific hydrocarbons and chemicals, you
can expose both the reference sample and the test
sample to the UV light source in the spectrometer.
7. A reading of 0 in the spectrometer indicates that the test
has passed and no hydrocarbons are present.
8. Factors that could affect this test are:
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Hazy test samples
Dirty Column
Damp bulkhead
Sweat
Chloride (Cl) Test
1. Using the same sample/nessler tube in which the
hydrocarbon (HC)/water miscibility tests were conducted
(if no hydrocarbons were found), add 5 drops of a 10%
silver nitrate solution, and then add 5 drops of a nitric
acid solution or use 5 drops of acidified silver nitrate
solution
2. Stopper the tube and invert it to mix the contents and
wait for 15 minutes.
3. Observe if any turbidity is formed by comparing the
sample with the standard. Look down through the liquid
against a black background to assess the turbidity.
4. The comparison of wall wash samples to a standard
should be performed in a darkened room by looking
down through the tubes using a wide-beam penlight
held about one foot from the sides of the tubes.
5. For preparing a standard solution for the chloride
solution:
6. Now we have both the standard solution and the wall
wash sample ready to run into the spectrometer.
Permanganate time test(PTT)
1. Thoroughly clean the sample/Nessler tubes with
hydrochloric acid and rinse them three times with tap
water. After that, rinse the tubes twice with deionised
water and twice with methanol.
2. Label the test tubes and add 50 ml of wall wash to each
tube.
3. Mix the permanganate solution by combining 0.1 grams
of potassium permanganate with 500 ml of Deionised
water(D.I. Water). Prepare a fresh solution every 3 days.
4. Before adding the permanganate solution, fill the tubes
to the 50 ml level with a wall wash.
5. Place the tubes in a water bath maintained at 15°C±1°C
if methanol is used, 25°C±1°C if acetone is used for ten
minutes.
6. Add 2 ml of the permanganate solution to each tube,
stopper the tubes, and invert them once to mix.
7. Prepare a standard solution using 50 ml of lab methanol
and 2 ml of the permanganate solution to run
simultaneously with the other tubes.
8. Place the tubes in the water bath in a dark place
and maintain the temperature.
9. Observe the colour at 10-minute intervals and make a
note of the times when the colour changes from deep
purple to pink and when it fades to a pale, watery yellow
and brown.
10.
If the standard fades at a shorter time than the test
sample, it indicates a problem with the lab, methanol,
permanganate solution, or testing containers.
11.
Now run the test in a spectrometer. For samples
with a reading above 32.0%, they will show a pink colour
and pass the test. For samples with a reading below
32.0%, they will appear brown in colour and fail the test.
Note: Permanganate time test(PTT) must be > 50 min.s
In addition to the aforementioned wall wash tests, other
important tests are also carried out, such as
Visual Test: This test involves visually inspecting the sample
under suitable lighting conditions to detect the presence of
any suspended particles or visible impurities.
Odour Test: The odour test is performed to identify any
persistent foreign odour that might contaminate the cargo.
Filter papers are dipped into both the sample and the
standard solution, and immediate smell detection is
performed. It is crucial to avoid directly smelling from the
tube, particularly if the previous cargo contained toxic
substances.
Non-volatile Matter (NVM) Test: The NVM test aims to
determine the presence of non-volatile impurities on the tank
surface. A specific quantity of the wall wash liquid is
evaporated, and the resulting residue (Non-volatile Matter) is
weighed. The weight of the residue is then divided by the
original sample weight to calculate the non-volatile matter
content.