Pressure Testing
Pressure Testing is used to determine the pressure that a system can take before the parts that compose that system experience undue strain. Pipeline, tanks, etc. that experience high levels of pressure that they are not designed for can experience damage to the integrity of their material over time if unable to withstand the pressure of the liquid or gas they contain. This can lead to ruptures and explosions that can damage expensive systems or cause severe injury!
There are two kinds of pressure testing: Pneumatic Testing and Hydrostatic Testing. Pneumatic Testing uses nitrogen or other non-flammable, non-toxic gas to test how much pressure in psi the system can handle. The pressure is held for a period of time to ensure that the strain the part is under will not cause the part to rupture. At TMC, pneumatic testing is performed from behind a blast wall, and leaks are identified by finding any place where bubbles escape the system once the pressure testing begins. When a leak is identified it must be fixed before pressure testing can resume, otherwise the results will be inaccurate.
The second kind of pressure testing is hydrostatic testing, which is considered far safer and easier to maintain. Water is used to fill the part under pressure, and, like pneumatic testing, is held at a certain pressure for a period of time to test strain on the material and identify the potential for leaks. Leaks are identified by water that leaves the system.
Pressure testing should always be performed to a much higher level than what is required in normal operation of the system. There are a few reasons to do this; if your system is under a lot of pressure strain for a long time, it is good to pressure test to a higher level of pressure to ensure that the parts won’t fail due to stress over time, or that they won’t rupture immediately if there a failure occurs that causes an unexpected pressure buildup.
When should I pressure test?
Pressure testing should be performed after any welding or heat treatment is done on a part or a line. If testing is being performed on a pipeline, the line should already be laid underground. This way the pressure testing can ensure that none of the material properties were compromised to the point of noncompliance, risking rupture and failure of the part, when heat was applied.
If a line is clean but still needs to be pressure tested, it can be pneumatically tested using filtered Nitrogen. This will test the pressure limits of the system without introducing particulate that was not previously present. However, as stated before, it is preferable to perform cleaning on your system, if needed, after the pressure testing occurs.
Should I use hydrostatic or pneumatic pressure?
Hydrostatic or Pneumatic testing should also be performed before precision cleaning happens. This ensures that none of the cleaning process is reversed, and new particulate or residue is not introduced to the system after cleaning.
Hydrostatic testing is far safer than pneumatic testing because water is incompressible, so it will store less potential energy and therefore will not break the container as harshly. If unable to handle the pressure, a hydrostatic test will rupture the part rather than causing a blast.
For this reason, pneumatic testing is only performed on a system if the design or function of the parts will not allow for a liquid to fill and flow through them. If it should never have water in it, use pneumatic pressure testing!
Pneumatic testing can only safely be performed at a maximum of 110% of the design pressure. You also have to have a relief valve in place to ensure that the pressure in the vessel being tested does not exceed the determined testing pressure and put workers at risk.
What extent of pressure test can TMC do?
Hydrostatic Testing
TMC can perform hydrostatic pressure testing up to 50,000 kPa. We work with customers to hold the pressure level they require for the amount of time that is required. We are equipped with flanges and connectors of a variety of sizes, and are happy to work with our customers to verify the material stability of their parts and assemblies.
Pneumatic Testing
TMC can do pneumatic testing up to 25,000 PSI. Parts are filled with gaseous Nitrogen (GN2) and held at customer recommended pressure for the amount of time that the customer requests. We also have built a blast wall in our facility to protect our employees from injury when performing pneumatic testing.