Colour Compare Test
Certain impurities result in discoloration of the wall wash sample. The colour of the wall wash liquid is compared with unused wall wash solvent. Mostly the so-called Alpha colour is measured.
Acid Wash Test
The Acid Wash Test Method is used to determine the presence of Benzene, Toluene, Xylenes, refined Solvent Naphthas, and similar industrial aromatic hydrocarbons. This test is also used for detecting of impurities in methanol. Compounds which cause darkening in the presence of concentrated sulphuric acid due to carbonization can be detected with this test. In Methanol analysis this is often referred to as Carbonizables.
Testing Procedure for Chlorides
The Chloride test is used to judge the presence of chlorides on bulkheads etc. Chloride levels vary from 0.1 ppm to 5 ppm depending on the requirement of the charterer. Chlorides will react with Silver Nitrate/Nitric Acid solution forming Silver Chloride (AgCl) which makes the solution turbid. By comparing the sample solution with the various prepared standard solutions one can establish the ppm chlorides in the wall wash.
Using the same tube in which the water miscibility test was done (if no hydrocarbons were found), add 5 drops of Nitric Acid solution and check for turbidity. Provided sample remains clear, add 5 drops of 10% Silver Nitrate solution. Stopper and invert the tube to mix and observe if any turbidity is formed. To do this, compare the turbidity of the sample with the standard by looking down through the liquid against a black background. Comparison of wall wash samples to a standard should be done in a darkened room, by looking down through the tubes using a wide beam flashlight held about one foot from the side of the tubes. A standard solution for varying amounts of chloride levels may be prepared from the standard chloride solution which should be included in the Methanol Test Kit. As chloride levels vary from 0.3 PPM from various charterers / suppliers, it will be necessary to gauge cleaning with regard to various chloride levels.
The most effective method for reducing chloride levels is to flush with copious amount of chloride free water. In Vancouver, for instance, this is not a critical problem as dock water is virtually chloride – free. However, in Kitimat there is no fresh water lines on the dock and fresh water can only be supplied by tank truck in 10 ton loads. i.e. very expensive and time consuming. In Al Jubail, initial indication are that there will be no fresh water available.
To assist in determining the chloride levels in wall wash samples, we will arrange to supply your request in Houston and Yokohama, a chloride sample. This will be delivered in quart bottles and mixed as follows. “Take 1 ML of the chloride standard and same to 25 ML of laboratory pure methanol. To this add 75 ML of deionized water. This solution will have the turbidity equivalent to 1 PPM chloride. To make a higher chloride standard, just increase above procedure accordingly. i.e. for a 2 PPM chloride solution just add 2 ML of standard to 25 ML of methanol and add 75 ML D.I. water, etc.”
Testing of Hydrocarbons
The purpose of this test is the qualitative detection of non-water-soluble contaminants. It works on the basis that many impurities are soluble in the wall wash liquid (Methanol, Acetone) but not in water. Sometimes this test is also called Hydrocarbon test. Using a clean Nessler Tube, pour 25 ML of wall wash from sample jar. To this add 75 ML of deionized water. Stopper and invert tube to mix same and allow to stand for about 20 minutes. Place the tube on a black surface. Turn off lights to darken room and shine a light through the side of the tubes while looking down through the liquid column. A wide beam flashlight should be used and kept about six inches from the columns.
Frequently, a pen light is used for this test. This is more critical due to the intensity of the beam. If this method is used on a standard (25 ML of laboratory pure methanol and 75 ML of distilled water), even in the standard there will sometimes be a faint whitish trace when using a pen light.
A standard solution, consisting of 25 ML of laboratory methanol and 75 ML of deionized water should be prepared to compare to the wall wash samples. If a bluish tint is present, there are moderate to heavy hydrocarbons. If a whitish haze is observed, this usually indicates slight hydrocarbons. Factors which could affect this test are: if the graduation numbers on the tubes are in blue, if the column is dirty, or if the bulkhead is damp!
- Regarding item #4, the hydrochloric acid/peroxide mixture is used to rinse the tube in which the permanganate time tests are done. These tubes will discolor to a color after about 3 successive time tests are run. To remove this discoloration and before using again, rinse with acid, flush 3 times with tap water, twice with deionized water, and twice with methanol. The solution should be made just prior to use and disposed of as soon as possible.
- Item # 6, filter , can be used to simulate laboratory conditions in tanks which are deemed borderline. Normally, one paper is used on each bulkhead, placed in a jar (using plastic gloves) and diluted with 50 ML of pure methanol for each filter paper. It is recommended that filter papers are tested for chlorides prior to use.
- Item #16, glass jars are for use in catching wall wash liquid to transport samples from tank to testing area.
Should you have difficulty in obtaining any of the above tested materials, please do not hesitate to contact us for assistance.
Permagnate Time Test
Permanganate-Time-Test ( oxidation test ) The Permanganate time is used to judge the presence of oxidizable materials that may be associated with contamination during distribution and to access compliance with a specification. The test is based on the ability of potassium permanganate (KMnO4) to oxidise hydrocarbon impurities that could be present in the wall wash liquid. If there is a reaction in a neutral solution, the potassium permanganate is reduced and changes its colour from pink-orange to yellow-orange. The more impurities the faster a change in colour occurs.
Of all the tests performed on board, this one is subject to error due to its complexity. Ideally, Nessler Tubes, used for testing, will have been thoroughly cleaned with hydrochloric acid and rinsed 3 times with tap water, twice with deionized water and twice with methanol. Then 50 ML of wall wash should be added to the previously labeled test tubes. To this, add 2 ML of the previously mixed permanganate solution. The pipette used for this should be thoroughly rinsed prior to use. As dispensette ( a bottle with a pump top, calibrated for 2 ML delivery) is the best method for introducing the solution: however a cleaned pipette is amply good. The preparation of a new permanganate solution (.1 gram of potassium permanganate to ½ liter of distilled water should ) should be done every 3 days. This solution should be stored in an amber-colored bottle in a cool, dark place.
Before adding the permanganate solution, fill the tubes to the 50 ML level with wall wash and place in a water bath which is maintained at 15 degrees Celsius(+/- 1 degree Celsius) for ten minutes. Then add 2 ML of solution to each tube, stopper and invert once to mix, nothing the exact time. The tubes containing wall wash to which 2 ML of permanganate solution is added should have their stoppers rinsed with methanol before inverting to mix the solution. A dirty stopper could affect the time test. Place the tubes in the bath in a dark place which is being maintained at 15 degree Celsius. Determine the intensity of the pink color at 10 minute intervals. Report the minutes elapsed between the time the permanganate was added and the time the pink color matches the standard.
It is helpful to make a standard solution to be run with each group of test tubes. This is made up by using 50 ML of lab. Methanol ( used for the wall washing) and 2 ML of the permanganate solution and run simultaneously with the other tubes. Therefore, if the standard fades at less time than you are testing for, it is an indication of a problem with either the lab. Methanol, the permanganate solution, or the testing containers. Under the purest conditions, the permanganate time test will run 120 minutes.
Wall Wash Procedure
Suggest using a plastic bucket to transport material for obtaining wall wash samples. Carry in bucket, plastic spray bottles, plastic gloves, funnel and jars for the number of tanks to be sampled. Items in bucket are to be rinsed with methanol after entering tank and before taking wall wash. Mark each bottle with tank number. Random select one spot on each bulkhead for methanol rinse. Holding funnel and sample jar in one hand, use spray bottle to wash an area directed at a minimum of three feet above funnel and jar ( four to five feet is preferable). By collecting about 25 ML if wash for each bulkhead, you will have enough to use for testing. It is extremely important that surfaces to be methanol washed are dry. If the laboratory area us neat and orderly, it will greatly facilitate testing. Ideally, if a refrigerator is nearby, it can be set to 15 degree Celsius for permanganate testing. There must also be a sink for rinsing material.
Used to determine if there are non-volatile impurities on the tank surface. A defined quantity of the wall wash liquid is evaporated. The weight of the residue, the so-called NVM (Non Volatile Matter), is detected by weighing. This is then divided by the original weight of the sample. The NVM content must not exceed the value specified by the loader
The UV-Test is used to identify certain hydrocarbons and chemicals. Many hydrocarbons and chemicals have the ability to absorb UV-light when they are exposed to such light. Certain molecular electrons will get exited if exposed to light. This exitation results in absorbance of light which can be measured. Absorbance at a specific wavelength is a measure for concentration of specific compounds. In a special apparatus called Spectrometer a sample (containing hydrocarbons) and a reference sample (containing just a solvent such as methanol) are exposed to a UV light source.