Question

Explain why the gas containers need to be very strong

Answer 1

In order to hold any useful quantity of gas the gas needs to be highly pressurised. It pushes against the sides of the container trying to force it apart so the container has to be very strong. If a gas cylinder ruptures the rapidly expanding gas can blow the cylinder apart & do a lot of damage. If the gas is flammable like LPG it's even worse because the gas burns, expands & boils at the same time. This is called a BLEVE or "boiling liquid expanding vapour explosion". Gas cylinders are tested using a liquid - usually water under pressure. When the cylinder breaks when pressurised with water all that happens after the cylinder fails is it just cracks because the water doesn't have to expand to drop it's pressure. A gas pressurised to 200 bar has to expand 200 times to drop it's pressure to the same as the atmosphere. Gas cylinders are designed to handle these kind of pressures but have to be tested every so often to remain in service.