The choice of method of loading and discharge will depend upon the relative position of the storage tanks and upon the hazard rating or nature of the cargo.

Cargoes which are not hazardous or noxious and which do not require protection from oxygen or water vapour may be loaded by any of the methods shown:

Noxious or hazardous cargoes
Loading or discharge through the top or bottom outlet maybe necessary. To create the totally closed system any air, gas or vapour displaced by the liquid must be returned to the storage tank through a vapour return line fitted between the airline connection and the storage tank.

Cargoes which must not be contaminated by oxygen or water vapour should be loaded through the top or bottom outlet.
The tank should be purged of air before loading and the cargo should be carried under a blanket of inert gas. Cargoes which foam or are susceptible to oxidation should be loaded through the bottom outlet, or if this is not possible, through the top outlet and syphon pipe.

Measurement of cargo
The quantity loaded can be measured on a flow meter, by using a diprod, or by means of a weighbridge. With hazardous cargoes and ‘closed system’ loading dip rods should not be used.

Check the complete system
All equipment from the main product storage tanks through to the tank container, including valves, hoses, pumps, gauges, connections, vapour return lines etc, should be regarded as a ‘total system ’ exposed to the same cargo characteristics, (viscosity, corrosivity, temperature and pressures), and must be thoroughly checked for suitability and condition.