• Computerized hydrostatic, internal pressure testing, up
to 7500 psi, is performed using various fluid media.
Hydrostatic tests are conducted under the constraints of
either the industry's or the customer's specifications.
The vessel is filled with a nearly incompressible liquid -
usually water or oil - and examined for leaks or permanent
changes in shape. Red or fluorescent dyes are usually
added to the water to make leaks easier to see.
The test pressure is always considerably higher than the
operating pressure to give a margin for safety. This
margin of safety is typically 150% or 5/3 of the design
pressure, depending on the regulations that apply. For
example, if a cylinder was rated to DOT-2015 PSI
(approximately 139 bar), it would be tested at around 3360
PSI (approximately 232 bar). Water is commonly used
because it is almost incompressible (compressible only by
weight, not air pressure), so will only expand by a very
small amount should the vessel split.
If high pressure gas were used, then the gas would expand
to perhaps several hundred times its compressed volume in
an explosion, with the attendant risk of damage or injury.
This is the risk which the testing is intended to