test method in degrees Celsius is tentatively estimated for average crude oils to be approximately 8°C at any pressure level. Therefore, deviations in excess of 6°C shall be considered suspect (see Note X2.7).
X188.8.131.52 The following causes for excess deviations of ECP from AET can be identified.
(a) If the ECP is consistently and significantly higher or lower than the AET, it is an indication of incorrect temperature measurement, Check Annex A4-Annex A6.
(b) If the difference between ECP and AET is significantly larger at one or more reduced pressure level(s), it is an indication for incorrect pressure measurement. Check Annex A6.
(c) Incorrect efficiency (too low). Refer to X2.7.4.
(d) Incorrect sample size (too small) with respect to column diameter or dynamic hold-up, or both. Check Table 1 or Annex A2, or both.
(e) Excessive heat loss. Evidence for the latter can also be obtained by careful examination of the T versus X plot (X2.6.8). In case of excessive heat loss the distribution will be asymmetrical, evidenced by significantly more outlying points at the high end of the temperature scale than at the low end. An overheated mantle (184.108.40.206) will lead to a too low ECP in comparison to the targeted AET.
Note X2.7—The setting of acceptable tolerance limits to trigger corrective action is the responsibility of the laboratory. However, the limit given has been proven indicative of incorrect performance in many years of application of Test Method D 2892.
Note X2.8—Too high efficiency will have no measurable effect on the ECP-AET differential.
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