Hydrostatic and Pneumatic Test

Hydrostatic = liquid test fluid (water, oil, etc.)
Pneumatic = gaseous test fluid (air, nitrogen, etc.)

Codes vary and are evolving. A common standard has been for hydrostatic test pressure to be 1.5 x allowable working pressure, and pneumatic to be 1.25 x. This depends on locale, however.

Hydrostatic test - Wikipedia, the free encyclopedia

Pneumatics - Wikipedia, the free encyclopedia

We always prefer Hydraulic test over Pneumatic tests whereever use of water is permitted for testing. The reason is very important to understand.

Water being highly incompressible, a small change in volume requires a very high pressure compared to air /gases.

The water is used mainly from the safety point of view.

In case of failure of system under tested, the explosion will never take place with water as testing medium because a very low volume loss will bring the pressures to safe limit. Whereas in case of Pneumatic tests, the equipment under testing may explode because a very large amount of volume needs to vented.

So, it is NOT A QUESTION of VALUES...Just use haydraulic test wherever it is permitted and use the Values as defined by the DESIGN CODES applicable for yr piece of equipment.

Hope it clarifies.