12. Calculation
12.1 Calculate the mass % water in a crude oil sample as follows:
where:
W1 = mass of water titrated, µg and
W2 = mass of sample used, µg.
12.2 Calculate the volume % water in a crude oil sample as follows:
where:
V1 = volume of water titrated, µL (same as the µg of water reported by the coulometric titrator) and
V2 = volume sample used, µL.
13. Report
13.1 When determining % water by mass, report the water content to the nearest 0.01 mass %.
13.2 When determining % water by volume, report the water content to the nearest 0.01 volume %.
14. Precision and Bias
14.1 The precision of this test method as determined by the statistical examination of interlaboratory test results is as follows:
14.1.1 Repeatability - The difference between successive results obtained by the same operator with the same apparatus under constant operating conditions on identical test material would, in the long run, in the normal and correct operation of the test method, exceed the following values only in one case in twenty (see Table 2).
14.1.1.1 For determinations of water by mass,
where:
X = sample mean from 0.02 to 5 mass %.
14.1.1.2 For determinations of water by volume,
where:
X = sample mean from 0.02 to 5 volume %.
14.1.2 Reproducibility - The difference between two single and independent results obtained by different operators working in different laboratories on identical test material would, in the long run, exceed the following values only in one case in twenty (see Table 2).
14.1.2.1 For determinations of water by mass,
where:
X = sample mean from 0.02 to 5 mass %.
14.1.2.2 For determinations of water by volume,
where:
X = sample mean from 0.02 to 5 volume %.
14.2 Bias:
14.2.1 No significant difference was found between the average water content obtained by this test method and the expected water content (based on the amount of added water) for the crude oil samples analyzed in the round robin used to evaluate the precision of this test method.
14.2.2 The interference from mercaptan sulfur follows the theoretical stoichiometry of 1 to 0.28, that is 1000 µg/g (ppm) of mercaptan sulfur can generate a response equivalent to 280 µg/g (ppm) water by this test method. The interference from H2S sulfur follows the stoichiometry of 1 to 0.56, that is 1000 µg/g (ppm) of hydrogen sulfide sulfur can generate a response equivalent to 560 µg/g (ppm) water by this test method. The validity of correcting measured water contents for known mercaptan/sulfide levels has not yet been determined.
15. Keywords
15.1 coulometric; crude oils; homogenization; Karl Fischer; shear mixer; titration; water; water in crude oils