Hazards of Water in Petroleum Products and the Significance of Trace Moisture Measurement

Hazards of water in petroleum products

The relative molecular mass of water is far smaller than that of oil, and its volume surges on vaporization, increasing system pressure drop and power consumption. High water content therefore causes operating fluctuations and flooding of columns. Inorganic salts brought in with the water (CaCl2, MgCl2) also intensify corrosion of the unit. Water in light fuel oils raises the freezing and crystallization points, worsening low-temperature fluidity, so that ice crystals separate at low temperature and block filters and oil lines—water in jet fuel and diesel in particular can interrupt fuel supply and cause serious accidents. Water in lubricating oils destroys the lubricating film, prevents normal lubrication, and increases mechanical wear; the inorganic salts it carries increase the oil's corrosivity and aggravate corrosion of parts. When a water-containing lubricating oil operates at elevated temperature, vaporization of the water destroys the lubricating film. Excessive water in reformer feed poisons the catalyst: the excess water occupies the catalyst's acid sites, destroys the balance between acid and metal sites, reduces catalyst activity or even deactivates it, and shortens catalyst life. Water content is therefore an indispensable quality indicator in the standards for all oil products.

The significance of trace moisture measurement

1. Measuring the water in oil products enables accurate quantity accounting: after gauging, subtracting the water volume gives the actual amount of oil in the tank.

2. Determining the water content allows a suitable dehydration method to be chosen according to its level, preventing the following hazards: for example, water evaporating from petroleum products absorbs heat and lowers the calorific value.

3. Water in light petroleum products worsens combustion and carries dissolved salts into the cylinders, forming carbon deposits and increasing cylinder wear; at low temperature, water in fuel freezes, blocking fuel lines and filters and obstructing fuel supply to the engine fuel system.

4. Water accelerates oxidation and gum formation in oil products; water in lubricating oil not only corrodes engine parts but also turns to steam on contact with metal parts above 100 °C, destroying the lubricating film.

5. Light oil products, with low density and viscosity, separate from water easily; heavy oil products do the opposite and are hard to separate. Crude entering atmospheric and vacuum distillation units must contain no more than 0.2%–0.5% water; finished product specifications require gasoline and kerosene to be water-free, light diesel to contain no more than a trace of water, and heavy diesel no more than 0.5%–1.5%; lubricating oils and fuel oils each have their own control limits.

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