Originally Posted by 2door
Be very very careful trying this. Unless you have a good understanding of metal, welding and the pressures you'd be working with, you could be injured. Hydro forming metal is a job best left to those with the knowledge and the proper equipment. Simply pumping water into a closed vessel without careful engineering could produce a very effective 'pipe bomb'.
Water is commonly used because it is nearly incompressible, therefore requiring relatively little work to develop a high pressure, and is therefore also only able to release a small amount of energy in case of a failure - only a small volume will escape under high pressure if the container fails. If high pressure gas were used, then the gas would expand to pV=nRT with its compressed volume resulting in an explosion, with the attendant risk of damage or injury. This is the risk which the testing is intended to mitigate.
The cylinder failed at 550bars/8,000psi water pressure during an extended proof test to investigate how the cylinder would rupture after failing visual inspection with extensive internal corrosion.
now just using airpressure alone at under 200psi and we get
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