Pressure testing procedures are key to ensuring the integrity of a wide variety of industrial components and equipment – including pipes, tanks, pressure vessels, fittings, and more. These tests are vital in both new component manufacturing, during routine maintenance, and quality verification of a component.
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Pressure testing can be done using two different methodologies:: hydrostatic and pneumatic. Hydrostatic tests utilize water as a medium, while the latter uses gas. There are important differences between both, most notably the level of energy released at failure. Let’s explore those differences and how we can keep your staff safe under both scenarios.
Hydrotest or hydrostatic testing is typically used for higher pressure components. Although water is most commonly used, other fluids such as oil or hydraulic fluid are sometimes used based on the materials under test and corrosion considerations.
On the other hand, pneumatic testing is regularly used for lower pressure components. Air is commonly used as the test medium, although another gas such as nitrogen can also be used in particular circumstances where low chemical reactivity is desired.
It is important to understand that water or oil are considered to be incompressible under the most reasonable pressures used in pressure testing. This is beneficial in that the test requires less energy to exert the required pressure than if a compressible medium is used. Less energy in means less energy out in the case of a failure.
Because pneumatic tests use a compressible gas, more energy is required to reach the required pressure. This energy is stored in the compressed gas and can be released explosively on failure. For this reason, pneumatic testing represents a significant hazard above and beyond hydrostatic testing. How much of a hazard?
An explosion of 200 ft. of 36 in. pipe containing 500 psi of pressure can create a blast wave nearly equivalent to 80 lb of TNT.
Pneumatic testing is much more dangerous than hydrostatic testing. Pneumatic testing requires higher levels of training, a pressure relief device is mandatory, and a higher safety rating of an enclosure such as TotalShield’s Shielding Rooms or Machine Enclosure is needed.
Based on the higher risk associated with pneumatic pressure testing, should hydrostatic testing always be used? Well, not necessarily. Let’s look at some of the considerations.
No matter which pressure testing process is used, the safety of your staff should be a top priority. Let’s discuss now how to ensure safety during both pressure testing processes.
In the case of hydrostatic pressure testing, there is a risk of injury from a high-pressure stream of liquid hitting the operator or the possible expulsion of a subcomponent such as a bolt or flange at high velocity. To prevent injury, all test components should be secured to avoid movement under pressure.
These are some hydrotest pressure safety protocols you should follow:
TotalShield manufactures a range of pressure testing blast containment products to add a final level of protection for hydrostatic testing. We can provide blast and impact-resistant Shielding Rooms for testing on larger items or smaller benchtop mounted enclosures for small components.
In either case, we work with the operator of the hydrostatic test to determine likely modes of failure and then calculate the energy associated with the ballistic impact of an ejected subcomponent.
It is critical to analyze the size and mass of every component that might be ejected and then design an enclosure with a margin of safety to contain those ballistic objects. Our engineers can also work with your team to create inlet and outlet ports in the enclosure for test fittings such as fluid hoses and drains.
As we’ve mentioned before, the risks associated with pneumatic testing are much greater than in a hydrostatic scenario. Like hydrostatic testing, there is the threat that an object will be ejected ballistically. There is also a risk of explosive blast. Put simply, an object under pneumatic pressure becomes a bomb, and at higher pressures, the explosive energies associated with a failure can be catastrophic.
Remember, we are adding significant amounts of energy to the system to compress the gas enough to reach the desired pressure. Upon rupture, that energy is released. This can result in an explosive event that releases a pressure wave and shrapnel and can result in grievous injury or death.
All of the safety precautions mentioned above for hydrostatic testing also apply to pneumatic testing. In addition, a pressure relief device should be considered to any pneumatic testing. These devices can take many forms: a simple plug designed to be ejected above a certain pressure, safety valves, or relief valves can be used.
The training of personnel is also vitally important in pneumatic testing. Only employees who have the required training and experience should be allowed to conduct pneumatic testing.
TotalShield’s shield pneumatic pressure testing enclosures are designed with a margin of safety for both ballistic failure and stored energy release in the pneumatic testing scenario. We work with your team to determine the total pressurized volume and total mass of the Unit Under Test (UUT) to ensure that you receive an enclosure certified to keep your staff safe in the event of failure.
Both pneumatic and hydrostatic testing play a vital role in manufacturing and maintenance. When done properly, these are safe activities.
Our engineers can help you design a shielding room, shield pressure testing enclosure, or ballistic shielding blanket that will keep your people safe while doing pneumatic and hydrostatic testing.
Industrial components need to undergo pressure testing to determine their structural integrity before use.
Components like pipes and pipelines undergo pressure-mediated checks to ensure they meet the relevant industrial safety standards.
One way to test these pipelines is through hydrostatic testing.
The article below will discuss hydrostatic testing and why it's essential.
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Hydrostatic testing plays an essential role in quality control.
Hydrostatic tests are administered to check the strength and usefulness of items like gas cylinders, storage tanks, pipes, and chemical pipelines.
Hydrostatic testing works by filling objects with water.
Following that, the water is pressurized inside the pipeline or vessel to make sure it can handle the pressures of everyday usage.
Typically, water is used for the liquid in the hydrostatic pressure testing process unless it could damage the pipe or vessel.
This guarantees that it can withstand pressure without splitting at its seams or letting any leaks occur in its structure.
Following ASME hydrostatic test regulations, vents must be placed on the pipe or vessel's high points before starting the test to remove any trapped air as water is added.
The test cannot be completed until the air is cleared.
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The name comes from when engineers used compressed air as their hydraulic fluid instead of water.
“Hydro” means water in Greek and “statikos,” means solid, as in static.
Through hydrostatic testing, we can gain confidence that the object won't rupture or leak when exposed to pressure or corrosive conditions.
Three common hydrostatic testing techniques are used to test vessels and cylinders.
Those tests are the water jacket method, the direct expansion method, and the proof pressure testing method.
The water jacket method requires placing the vessel in a closed chamber, referred to as the test jacket, and filling it with water.
The test jacket is also filled with water.
The vessel is pressurized inside the test jacket for a pre-determined amount of time.
The vessel is expanded within the test jacket, causing water to flow into a glass tube so it can be measured for total expansion.
The total expansion is recorded, and the vessel is depressurized so it can return to its original size.
Sometimes the vessel won't return to its original size.
When that happens, it's called permanent expansion.
The serviceability of the vessel is determined by comparing total expansion to permanent expansion.
The larger the percentage increase, the more likely the vessel will be retired.
The direct expansion method involves filling a vessel or cylinder with a specified amount of water.
Once filled with water, the system is pressurized and you measure the water level to see how much water was expelled when the pressure is released.
The permanent and total expansions are determined by calculating the amount of water forced into the vessel, the test pressure, and how much water was expelled from the vessel.
The proof pressure test applies internal pressure to discover any weak points or leaks due to wall thinning that might result in the failure of the vessel.
This method is only permitted in the U.S. when the U.S. Code of Federal Regulations doesn't require permanent and total expansion values to be recorded.
Hydrostatic testing services can determine if a vessel can hold the amount of pressure it’s rated for safely.
This process guarantees that weld joints and flanges on industrial equipment are installed correctly, and the material will be able to handle the pressure.
These testing requirements are especially important in industrial applications involving the storage and transportation of fuel, chemicals, and other hazardous materials.
These materials can explode if they fail under pressure, and in pipelines a weakness in the structural integrity of a pipe could dramatically impact both the environment and economy.
For hydrostatic testing to work in any form, you need quality equipment.
It's very important to use quality equipment for your testing and have it installed by an experienced company.
STEVENS has complete hydrostatic testing and documentation in place, as well as in-house chemical cleaning and flushing and protective coating capabilities.
If you need professionally installed hydrostatic testing equipment, don't hesitate to contact STEVENS.
References:
https://nigen.com/pneumatic-and-hydrostatic-pressure-testing-companies/
https://www.precgroup.com/hydrostatic-testing-what-is-it-how-does-it-work-and-what-are-the-benefits/
https://inspectioneering.com/tag/hydrostatic+testing
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