Objectives
Pressure testing ensures that tanks, vessels and piping systems, are correctly constructed. Testing ensures the integrity of flanged joints and threaded connections. Two objectives must be satisfied during the performance of the pressure test:
- Primary Objective: Demonstrate the integrity of the pressure boundary
- Secondary Objective: Minimize hazard to test personnel and existing facilities
Design Requirements
The governing code specifies the pressure testing requirements. Critical parameters for testing include:
- Method
- Test Pressure
- Duration
Types Of Testing
Pressure testing can be performed using water, compressed air or process fluid. An overview of test methods is provided below:
- Hydrostatic Testing: In a hydro test, piping, vessels and tanks are filled with water to check for leakage. When required, a small pump is used to pressurize the system to the required test pressure. Pressure is maintained while a leakage examination is conducted at connections.
- Pneumatic Testing: In a pneumatic test, piping, and vessels are filled with compressed air (or other gas) to check for leakage. A large compressor is needed to achieve the required test pressure. Pressure is maintained while a leakage examination is conducted at all connections. Leakage is detected by soap bubbles
- Initial Service Testing: In some cases hydrostatic and pneumatic testing is not practical. In an initial service test, the system is placed into service. A leakage exam is conducted with the system at operating pressure.
Testing Considerations
- Minimize Hazardous Test Energy: The potential for a rupture during testing must be assessed. A rupture can result in an immediate expulsion of stored energy. This can damage systems and injure personnel. Testing methods that limit the energy in the system should be considered. Water is nearly incompressible. A small amount of energy is required to to increase pressure. Air must be compressed to increase pressure. A pneumatic test may have over 1000 times the energy of a hydrostatic test.
- Process Contamination: The engineer should consider contaminant limitations of the process fluid. Hydrostatic testing can leave residual contaminants in the system. When this cannot be tolerated; the engineer should consider an Initial Service Test.
- Geometry & Venting: During a hydrotest, air will be compressed and trapped in local high points of the piping system. The presence of air can hinder leakage detection. The piping system should be designed with slope and high-point vents. This allows air to be purged from the system. Ultrasonic testing can be used to confirm the absence of any trapped air pockets.
- Specific Gravity: Steam and gas piping systems are designed to carry light contents. Hydrotesting of these systems, can create excessive loading on the piping system. A pipe stress analysis is needed to confirm the adequacy of the system.
- Combustibility: Flammable gases and liquids are routed in oxygen-free systems. Pneumatic testing with air can introduce oxygen into these piping systems. Following testing, process flow is introduced into the line. This can dilute contents below the Upper Explosive Limit (UEL). Once below the UEL, the contents may combust or explode. The engineer should specify a system purge with inert gas prior to restoration.
- Initial Service Testing: Supporting systems must be functional for the test. For example, steam systems can only be tested once enough heat is available to generate steam. Testing can be delayed until late in the project. This leaves little time for the project to recover if leakage is identified. Fixing a component may need draining of the system. This can waste expensive process chemical. The engineer should understand schedule constraints when considering an Initial Service Test.
Pressure Testing by XCEED
At, XCEED we have the tools to help develop your pressure testing plan. Our engineers weigh the benefits of each method. We develop testing boundaries and supporting analysis to conduct testing. For more information about our testing services, Contact Us.
One thought on “Pressure Testing”
I appreciate your explanation when you told us that during hydrostatic testing, the piping, vessels, and tanks are filled with water to check for leaks while pressure is maintained. I run a beer brewery business, and it seems like our factory needs to get our vessels and tanks checked for pressure soon. I’ll take note of this while I look for services in Tacoma to hire for hydrostatic testing soon.