Spirit flow-x Function Reference page 115

10. The relative density at [60 F, equilibrium pressure] is calculated from the density
at [60 F, equilibrium pressure]
11. Because API 11.2.1 requires the API gravity value at 60 F, the API gravity at [60
F, equilibrium pressure] is calculated from the density at [60 F, equilibrium
pressure].
12. The compressibility factor is calculated according to API MPMS 11.2.1 from the
API gravity at [60 F, equilibrium pressure] and the 'Observed temperature'. If API
11.2.1 rounding is enabled then the API gravity and temperature are rounded
and the calculations are performed in accordance with the rounding and
truncating rules of the standard.
13. The CPL value is calculated from the compressibility factor and the 'Observed
pressure' and 'Equilibrium pressure' input values.
14. The density at [60F, equilibrium pressure] is calculated by dividing the observed
density by CTL and the new CPL value.
15. If API2540 rounding is enabled then the density at [60F, equilibrium pressure]
value is rounded to 3 decimal places as specified in the standard.
16. The relative density at [60 F, equilibrium pressure] is calculated from the density
at [60 F, equilibrium pressure]
17. If API2540 rounding is enabled then the relative density at [60F, equilibrium
pressure] value is rounded to 4 decimal places as specified in the standard.
18. Steps 5 through 17 are repeated taking the density value from step 14 as the
start value for the next iteration until the absolute difference between two
consecutive density values is either 0.05 (or 0.07 for the transition area) or
0.000001, depending of API2540 rounding being enabled or not.
19. For refined products the entire iteration loop is repeated if the relative density at
[60F, equilibrium pressure] appears to be in a different product region than the
observed relative density. This is required because a different product region
means different K0, K1 and K2 factors.
20. If API 11.2.4 rounding is enabled, then the relative density value at [60F,
equilibrium pressure] is rounded to 0.0001
Conversion method 2: from standard to observed conditions.
The function performs straightforward calculations to determine the relative density at observed
conditions:
1. First the inputs are rounded in accordance with the API2540 standard, provided
that API2540 rounding is enabled.
2. The density at [60F, equilibrium pressure] is calculated from the input relative
density
3. When the type of product is set to 'B – Auto select' (automatic selection of the
refined product range) the K0, K1 and K2 factors are determined based on the
input relative density
4. The Alpha factor is calculated according from the density at [60F, equilibrium
pressure] and the K0, K1 and K2 factor. If API2540 rounding is enabled, then the
intermediate results are rounded or truncated as specified API-2540 Table 24.
5. The CTL value is calculated according to API-2540 Table 24 from the Alpha factor
and the differential temperature (= observed temperature – 60°F). If API2540
rounding is enabled, then the intermediate results are rounded or truncated as
specified API-2540 Table 24.
6. Depending on the type of API2540 rounding the calculated CTL value is rounded
to 4 or 5 decimal places or not rounded at all.
Because API 11.2.1 requires the API gravity value at 60 F, the API gravity at [60
7.
F, equilibrium pressure] is calculated from the density at [60 F, equilibrium
pressure].
Flow-X─ Function Reference
Flow-X General functions - fxAPI_RD60F_1980
4-115