Pneumatic Testing and Hydrostatic Testing for Pressure Vessels and Pipelines
Numerous areas of manufacturing, extraction, and production use pneumatic and hydrostatic testing to ensure the integrity of pipelines and vessels. This testing is generally required for safety reasons and to meet regulatory requirements. However, there is a lack of discussion about why this type of testing is necessary, what steps are required, and the options available.
In simple terms, the purpose of pneumatic and hydrostatic testing is to ensure a pipeline or vessel is free from leaks and can withstand the pressure of normal usage. Before being put into service or returned to service after repairs, many different types of industrial equipment and facilities require this testing. In many situations, government regulations clearly specify what testing is required. In addition, many companies have their own additional internal testing guidelines and policies.
The most commonly used set of specifications for pressure and leak testing is the ASME B31 Pressure Pipeline Code. This code details testing steps and requirements for different types of piping. Hydrostatic testing is performed with a liquid like water and pneumatic tests use a gas like nitrogen.
What Is Pneumatic Testing?
Pneumatic testing is the process of using a gas to determine if a vessel can safely withstand the pressures required under normal usage. To do this, a gas is inserted and the pressure is increased above the normal pressure the vessel is designed to withstand once put in service. The pneumatic testing will help to identify any leaks, faulty joints, or other operational issues.
Pneumatic Test Procedure for Pressure Vessels
Pressure vessels are any containers designed to hold materials at a different pressure than the ambient pressure outside of the vessel. Vessels that are designed to hold or transport liquids or gases under pressure require testing to ensure that they are free from leaks and can operate safely.
Pneumatic testing safety is of key importance so there are several steps required to perform a pneumatic leak test. Pressure vessel testing procedures require that all joints that have not previously been pressure tested be exposed so they can be examined during the test to make sure they are free from leaks. Adjacent equipment, vessels, or pipelines that are not being tested need to be isolated or disconnected before the test.
Pressure Vessel Testing Standards
Pneumatic leak tests need to be performed using a non-flammable gas. Air can be used but it is less desirable since that mixture of gases will include water molecules. This is an undesirable contaminant as moisture can accelerate corrosion. That is why dry nitrogen is the preferred gas to use in pneumatic pressure testing.
Pressure Testing Procedures for Pipelines
Pipelines are generally tested at 110% of the designed pressure for the pipeline. If desired, a preliminary pneumatic test at a lower pressure can be performed to check for any major leaks before the higher-pressure test. To facilitate pneumatic tests with nitrogen, on-site nitrogen generators can be conveniently located onsite. These generators are suitable for use anywhere–even remote locations.
Like with pressure vessels, all pipeline joints that have not previously been pressure tested must be exposed and checked for leaks during the test. Expansion joints can be temporarily isolated or equipped with temporary restraints prior to testing. The testing pressure must be maintained for at least 10 minutes. During that time, each joint and seam must be checked for leaks.
Pipe Pressure Testing Standards
Different requirements may apply but the most common pneumatic test procedure for piping is the ASME B31 Pressure Piping Code. Within that, ASME B31.1 is generally applied to power piping and ASME B31.3 is used for process piping. Refrigeration piping testing procedures are based on ASME B31.5.
Under ASME Section B31.1 pneumatic power piping testing is performed at a minimum of 1.2 times the design pressure, but less than 1.5 times. To reach that pressure, the test starts by increasing the pipeline’s pressure to .5 of design pressure. Then a preliminary inspection is performed to check for leaks. If no leaks are found, pressure is increased in the pipe in increments of .1 of design pressure until the target test pressure is reached. At that point, the pressure will be maintained for at least 10 minutes. The pressure is then reduced to design pressure or 700 kPa, whichever is lower. That pressure is maintained while the pipe is again checked for leaks.
Process piping pneumatic testing is done under ASME B31.3. The pipe is brought up to .5 of the design pressure or 170 kPa, whichever is less. At that point, all joints and seals are checked for leaks. Pressure is gradually increased holding at each increment long enough to equalize the piping strains. The pipe is eventually brought up to between 1.1 and 1.33 times the design pressure. Pressure is then reduced until it is to equal the design pressure. The pressure is held at that level for a minimum of 10 minutes during which the pipe will be checked for leaks.
What Is Hydrostatic Pressure Testing?
In hydrostatic pressure testing a liquid is used to check for leaks before putting a pressure vessel or pipeline into service. The liquid is pressurized within the pipeline or vessel to make sure that it can withstand the pressures of normal usage.
Hydrostatic Pressure Testing for Pipes and Pressure Vessels
In order to test, the pipe or pressure vessel must be filled with a liquid. The liquid used is typically water unless water will damage the pipe or vessel. To meet ASME hydrostatic test requirements, before the test begins, the high points of the pipe or vessel must have vents to allow any air to escape as water is added. All air must be cleared before the test can be completed.
ASME B31.1 Hydrostatic Test
Power piping is normally tested under the procedures outlined in ASME Section B31.1. For hydrostatic testing the ASME hydrostatic test pressure is 1.5 times the design pressure.
ASME B31.3 Hydrostatic Test
Process piping is tested under ASME Section B31.3. The ASME b31.3 hydrotest is performed at 1.5 times the design pressure.
ASME B31.5 Hydrostatic Test
ASME B31.5 hydrostatic testing code covers refrigerant, secondary coolant piping, and heat transfer components. These hydrostatic pressure testing standards apply to piping that can be used for temperatures as low as -320°F (-196°C).
Use of nitrogen for pressure testing effectively purges unwanted air and moisture, making the system ready to accept product once the testing has been completed. Click to learn more about NiGen’s pipeline maintenance services and how onsite nitrogen generators can help. Contact NiGen today for more information.