Seen from outside, two cylinders look alike; but a fuel tanker and an LPG tanker are vehicles from engineering-wise different worlds. The difference can be summed up in one sentence: fuel is liquid at atmospheric pressure, whereas LPG remains liquid only under pressure. The shell is therefore not a vessel but pressurised equipment.
How Pressure Shapes the Design
- Wall thickness and material: Continuous internal pressure demands thick-walled, pressure-vessel-certified steel; the thinness of an aluminium fuel shell does not apply here
- Cross-section and ends: Pressure necessitates a circular cross-section; the tank ends are closed not with flat covers but with domed forms
- No compartments: In contrast to the multi-compartment structure of a fuel tanker, a pressurised tank is generally a single volume; internal baffles manage the slosh
- Safety equipment: Pressure-relief valves, excess-flow shut-off valves and remotely operated internal safety bottom valves are the system's fuse
Habits That Differ in Operation
Because the volume of pressurised gas changes markedly with temperature, the tank is never filled completely; a safety volume for the liquid to expand into as it warms is left at every filling. Keeping the shell a light colour against sun exposure and using reflective surfaces are simple but effective measures that prevent unnecessary rises in internal pressure. Leak checking of connections during transfer is done with a detector, under a stricter discipline than the visual check used for fuel.
In short: designing an LPG tanker is not adding pressure to a liquid-carrying vehicle; it is carrying pressure-vessel engineering onto a chassis.