EXPLANATION
A knowledge of water extractable inorganic halides in crude oil is important in deciding whether or not the oil needs desalting. Excessive halides, especially in crude oil, frequently results in higher corrosion rates in refining units. This test method covers the determination of salt in crude oils. For the purpose of this test method, the salt is expressed as % (m/m) NaCl, and covers the range from 0.0005 - 0.15 % m/m. The detection limit of this test method is 0.0002 % m/m for salt as NaCl. This test method is applicable to nearly all of the heavier petroleum products, such as crude oils, residues, and fuel oils. It may also be applied to used turbine oil and marine diesel fuel to estimate seawater contamination. Water extractable salts, originating from additives present in oils, are codetermined.
TEST SUMMARY
After homogenizing the crude oil with a mixer, a weighed aliquot is dissolved in xylene at 65° C and extracted with specified volumes of alcohol, acetone, and water in an electrically heated extraction apparatus. A portion of the aqueous extract is analyzed for total halides by potentiometric titration with standard silver nitrate solution.
TEST PRECISION
Where X is the salt concentration in mass % as NaCl.
This procedure has no bias since the salt content is defined only in terms of this test method, and certified reference materials are not available. However, based on the spiked samples used in the interlaboratory study, the following observations can be made: Over the range of 0.0005 to 0.0400 mass % salt added, the recovery was constant and averaged 97 %. Over the range 0.0400 to 0.1500 mass % salt, the recovery was a function of concentration and gradually decreased from 97 % at 0.04 mass % to 88 % at the 0.15 mass % level.