Why cannot gas be used as a pressurizing medium for the pressure test of boiler vessels?
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“It is common knowledge that water is generally used as the pressurizing medium for pressure vessels in boilers; gases cannot be used as such a medium, as it is extremely dangerous. But why can’t gases be used? Where exactly lies the danger? Is there any experienced expert who can help answer this?
This post was last edited by zhangjuhua on 2018-9-2 at 16:34. It’s extremely dangerous – gases are compressible; when the container fails, the pressure doesn’t drop immediately, and the gas spreads everywhere, resulting in tremendous force and significant impact on the surroundings. Water, on the other hand, is incompressible; when the container breaks, water leaks out and the pressure stops rising and drops right away. It isn’t as destructive as gases, and its effect doesn’t last long
The risk associated with pneumatic testing is higher than that of hydraulic testing, as gases are compressible and can store a large amount of energy; once the equipment is damaged, the resulting harm can be severe. Therefore, safety measures must be in place when conducting pressure tests; such tests require approval from the unit’s chief technical officer, as well as on-site inspection and supervision by the unit’s safety department. For this reason, hydrotesting is always given priority.
Pressure testing includes hydraulic testing, pneumatic testing, and a combined water+air testing method. Hydraulic testing is the preferred option, as it is stable and reliable with a high safety factor. Pneumatic testing is not the first choice; if it is used, it is applied in situations where the pressure is low and the volume is small. The combined water+air testing method is generally used for devices with large volumes – using water alone results in high water consumption, and factors such as the foundation’s bearing capacity and hydrostatic pressure must be taken into account; using air alone poses a high risk level. So combine them
For those that meet the conditions for hydraulic testing, pneumatic testing is not recommended; since liquids are incompressible, pressure is released instantly in the event of a leak, which prevents damage to the equipment； Gases have a high compression ratio, which can cause significant damage to equipment and increase the safety risks for those conducting pressure tests.