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Determining water contamination in chemical cargo - Chemical tankers procedure

The range of chemicals shipped in bulk now has been increased enormously and to maintain product quality any contaminants in the chemical cargo need to be observed.

Presence of free water in non water-soluble products can, very roughly be determined on board by the following simple methods.

i) Warm a sample of the product in a test tube or in a bottle.Water will then collect at the bottom of the tube and can be seen after some time.

ii) Drop a little of the product on to an electric hot plate. A crackling sound indicates that water is present. Can be used on lubrication oils etc.

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Other methods for non water-soluble products are:

i) The product is kept at a temperature slightly above 100 degr. C for a period of time and is accurately weighed before and after heating (for products with a boiling point above about 125 degr. C).

ii) Use a centrifuge and see if there is any water at the bottom of the test tube.

iii) A distillation method according to ASTM D 95-62 (Dean Stark) is often used for oil products with relatively high boiling points (fuel oils, gas oil, asphalt, creosote). A sample is dissolved in xylene and the solution boiled in a glass retort. The vapours pass through a condensor. The water condenses and can be measured in a graduated tube.

An accurate determination of water contents can be made with a "Karl- Fischer" - reagent. This method is suited for laboratory work only.

Very small amounts of water in some products can be observed as a turbidity in a clear liquid when a sample is cooled down to a low temperature (cloud point). As a reference calibrated samples are used with known water contents at defined temperatures. The method is used primarily for chlorinated hydrocarbons such as carbon tetrachloride and trichlorethylene where water might be a severe contaminant also in minute concentrations (example: for trichlor ethylene a max water contents of e g 0, 006 %). (Remark: "cloud point'' also means the temperature at which wax needles may form in certain oils, e g in gas oil, upon cooling. Ref: ASTM D 2500-66).

Related Info:

Determining water contamination in chemical cargo

Chloride contamination in chemical cargo - how to resolve?

Varoius product contamination in chemical cargo - how to resolve?

Using acid wash method for a cargo of aromatics contaminated by a previous oil cargo

APHA (Hazen) method for determining color of very light chemical products

Use of Oxygen analysers

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