"Fred the Red Shirt" wrote in message
om...

IIUC Scuba tanks are routinely filled while submerged in water for
cooling purposes. In the examples I gave the vessels were pressure
tested while FILLED with water so that there was no compressed air
inside.

In the scuba example the water ouside the pressure vessel provides
(some I suppose) protection from the explosion should it fail.

In the earlier examples, filling the pressure vessel with water
prevents an explosion should the vessel fail.

Just to be clear.

Scuba tanks are filled with air while immersed for cooling and protection.
They are also hydrostatically tested every five years, during which they are
filled with water to mitigate expansion if they fail.

Rich S.