Ultra violet transmittance test

ULTRA VIOLET TRANSMITTANCE TEST DOCUMENT NAME: UV TEST What is Ultra Violet Transmittance? Ultra Violet Transmittance is the measurement of light on a specified wavelength, as it passes through a given amount of product The reading are based upon the absorbance or transmittance of UV light Ultra violet light for our testing purposes are given in the ranges of 200 upto 350 nm (nanometer) Typical points of measurement are 220 nm 269 nm - 275 nm 350 nm How is the test performed? A sample of the cargo (wall wash or bottom or foot sample) is placed with a blank and run through a spectrophotometer The spectrophotometer sends a ultra violet light through the sample and the blank with a double beam Any impurity shown in the cargo sample will block the passage of this light Results are given in transmittance (light allowed to pass through) or absorbance (light trapped in the sample) Ultra violet light results in a percentage readout that can be translated to a PPB (Parts Per Billion) reading on impurities Are all cargo equal in their specification? No! Each product is variable, also the sales specs of producer and / or receiver quite often vary Here are some typical products and their specification: Mono Ethylene Glycol UVTransmittance” at (350 nm, cm) = mm 98% at (275 nm, cm) = mm 90% at (220 nm, cm) = mm 70% Methanol UV Absorbance” at (250 nm, cm) = max 0,35 at (268,5 nm, cm) = max 0,0 17 Ethanol Petrobas Santos UV Absorbance at (200 nm, cm) = 0,22 at (250 nm, cm) = 0,02 at (270 nm, cm) = 0,01 ULTRA VIOLET TRANSMITTANCE TEST What are the UV transmittance/ absorbance reading telling us? The majority of products have a specified absorbance or transmittance in the ultra violet region Therefore any “pick up” of other products or impurities in the wall wash or foot sample will show very dirty What products will influence the UV test? AII ”aromatic products” e.g Benzene, Toluene, Xylene Solvent Naphtas etc Chlorinated Hydrocarbons, e.g Ethylene Chloride Perchloroethylene, Carbonetrachloride, Chloroform etc Petroleum products with high aromatic count, such as Naphta, Kerosene, Gasoline, Gasoil, White spirit All inhibited products, e.g Acrylonitrile, Methyl Methacrylate Monomer, Ethyl Acrylate Styrene Monomer etc What does this mean in practice? As can be noted from the mention list of last cargoes that will affect the UV test, a lot of these products are also used for tank cleaning purposes E.g should we toluene steam a cargo tank, followed by a fresh water wash, and get the wall wash testing results are Chlorides - Hydrocarbon free PTT 50 We should then feel very happy with our self, as this type of result is acceptable in most cases, however this can give a very negative result on the UV test Why? The UV test may pick up traces of the toluene even though it has been evaporated and washed with fresh water How can we meet such requirements? We must utilize a neutral solvent for the final flushing of the tank!! What can be considered as neutral solvents, that can also be utilized as flushing materials??? None aromatic hydrocarbons such as Alcohol’s, e.g high grade ethanol, methanol Ketones, acetone, MIBK, MEK -Should you encounter such testing methods, please keep us informed Note that flushing with products with flash point below 60C requires an inerted atmosphere tank  .. .ULTRA VIOLET TRANSMITTANCE TEST What are the UV transmittance/ absorbance reading telling us? The majority of products have a specified absorbance or transmittance in the ultra violet. .. affect the UV test, a lot of these products are also used for tank cleaning purposes E.g should we toluene steam a cargo tank, followed by a fresh water wash, and get the wall wash testing results... result is acceptable in most cases, however this can give a very negative result on the UV test Why? The UV test may pick up traces of the toluene even though it has been evaporated and washed with