Chemical Tankers / Day 4 / Day 4 Topic 2 Cargo Quantification
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Cargo Calculations
Information required to Calculate Load Figures:
From Surveyor:
a)Litreweight at Standard Temperature
b)Correction Factor per oC
From ship:
a)Observed Volume (Ullage)
b)Observed Temperature
Cargo Calculations
MT = obs vol (m3) x cL/W
Example 3: |
L/W: |
0.9071 at 15oC |
C/F: 0.00078/oC
Obs Ull: |
3.69m = 973.874 m3 |
Obs Temp: |
18.5oC |
To calculate tonnes loaded:-
Cargo Calculations
dT = 18.5 - 15 = 3.5
tC/F = 3.5 x 0.00078 = 0.00273
cL/W = 0.9071 - 0.00273 = 0.90437 (Hotter, so less)
MT = obs vol (m3) x cL/W = 973.874 X 0.90437
= 880.742 mt
Cargo Calculations
Information required to Calculate Load Figures (USA):
From Surveyor:
a)API Gravity or Lbs / Gall
b)Table - Volumetric Correction Factor ( VCF)
From Ship:
a)Observed Volume (Ullage)
b)Observed Temperature
Cargo Calculations
Traditional method in USA and US dependent countries, derived from the oil industry
Vessels loading computer may be able to handle this anyway
Request further info from surveyor
Request lbs / gall value for preference (sometimes in tabular form – it is easier to work with)
Cargo Calculations
If not, calculate the equivalent L/W and C/F
Various Correction Tables: ASTM 6A, 6B, 6C, 52,54A, 54B
Petroleum Tables are mostly entered with API Gravity, but some tables use
SG 60/60oF or Density (vacuum) as the principal argument ; Density (vacuum) - 0.0011 = Density (air) ie: L/W Note: For density values above 1.000, the correction becomes 0.0010
Cargo Calculations
To convert API Gravity to L/W:
|
141.5 |
= SG 60/60oF |
API Gravity + |
131.5 |
|
SG 60/60oF x 0.99799 = L/W
(Note: This will only give us L/W)
Cargo Calculations
Example 4:
API Gravity: 25.0
141.5 = 0.90415 (SG)
25.0 + 131.5
0.90415 x 0.99799 = 0.90234 (L/W)
(Now we need to calculate C/F)
Cargo Calculations
To calculate C/F:
Obtain dVCF: |
(VCF at 60oF = 1.000) |
1 - VCF at temp = dVCF
dVCF |
= VCF per oF |
temp interval dT |
|
VCF per oF x L/W = Corr per oF
Corr per oF x 1.8 = Corr per oC (or ./. by 0.556)
Cargo Calculations
Example 5:
Density (vac): 0.9503
Temp: 140 oF
VCF: 0.9662 (ex table)
(Note: Remember L/W is in air, ie: above density - 0.0011 = 0.9492)
To calculate Corr per oC :