The following example demonstrates the typical procedure outlined using the standard temperature of 15°C as applied to cargo in a ship’s tank.
Measurement data — Tank No.3 port
Product — Propane
Gauge reading of liquid depth ………………………………….. : 10.020 metres
Ship’s trim ……………………………………………………………. : 2.0 metres by stern
Ship’s list …………………………………………………………………. : 0.5° to port
Mean temperature of liquid ……………………………………….. : – 43°C
Mean temperature of vapour………………………………………. : – 38°C
Vapour space pressure ……………………………………………… : 59 mbarg
Molecular weight of liquid …………………………………………. : 44.097 given by
Density of liquid at 15°C ……………………………..…………….. : 511 kg/m3 shore
From ship’s calibration tables for Tank No.3 port
Correction for trim …………………………………………………… : – 127 mm
Correction for list ………………………………………….………….. : + 46 mm
Level gauge correction ………………………………………………. : + 1 mm
Float immersion correction ………………………………………… : + 0 mm
Corrected liquid depth = (10020 – 127 + 46 + 1 + 0)/1000 … = 9.940 metres
Volume of liquid at calibration temperature …………………. = 5441.88 m3
100 per cent tank volume at calibration temperature ……. : 9893.63 m3
Volume of vapour space at calibration temperature ……… = 4451.75 m3
Factor for tank contraction from calibration temperature to -43°C
……………………………………………………………………………………. : 0.99773
Factor for tank contraction from calibration temperature to -38°C
……………………………………………………………………………………. : 0.99791
Liquid calculation
Volume of liquid at calibration temperature …………………. : 5441.88 m3
Tank thermal correction factor (-43°C) ………………….……… : (x)0.99773
Volume of liquid at -43°C ……………………………………….…… = 5429.52 m3
Volume reduction factor from -43°C to 15°C from –
ASTM-IP Table 54 ………………………………………………………… : (x)1.145
Volume of liquid at 15°C ………………………………………..…… = 6216.8 m3
Density of liquid at 15°C (from shore) ……………………..…… : (x)511 kg/m3
Mass of liquid ………………………………………………….………… : 3176785 kg
Mass of liquid ………………………………………………..………….. = 3176785 kg
Mass of vapour ………………………………………………..………… = 10613 kg
Total mass …………………………………………………………..…….. = 3187398 kg
Weight-in-air
Factor for converting mass (weight-in-vacuo) to weight-in-air for liquid
of 511 kg/m3 density at 15°C from short table of ASTM-IP Table 56 …..
……………………………………………………………………………………. : (x)0.99775
Total weight-in-air………………………………………………………… = 3180226 kg
or 3180.23 metric tonnes
The above procedure and calculation requires to be duplicated before and after cargo transfer in order to obtain the weight of cargo transferred.
Sources : Liquefied Gas Handling Principles On Ships and in Terminals – McGuire and White