I do not know about other countries but here in Spain the valves on these bottles are soft soldered in place for 100% sealing and will unscrew easily if heated enough to soften the solder. I did not know this until after I struggled to remove my first one, then I could see why.
Of course it is best to ensure that the bottle has been well drained and vented first.
These bottles have numerous uses. I have used them for the media in blasting applications, sand and sodium bicarbonate. They can be used as compressed air cylinders which can be filled from a compressor at base and then taken into the field without the weight and bulk of a compressor. Their usefulness is only limited by imagination.