A hydrostatic pressure test helps find leaks in tanks and pipes. It is a procedure employed to assess the strength and weakness of piping systems, gas cylinders, boilers, pressure vessels, etc. If you suspect a plumbing leak, hydrostatic pressure testing is necessary for confirming its presence.
A hydrostatic pressure test is typically carried out after the equipment undergoes repair to authenticate that the equipment is fit to work under a desired set of conditions once it is returned to service.
You cannot perform the hydrostatic pressure test during normal operations. Additionally, you cannot screen the equipment for leaks after the test is complete. If you are looking to carry out on-stream equipment reliability, we suggest trying your luck with a fixed equipment mechanical integrity program.
The hydrostatic pressure test is considered a non-destructive testing method. However, it is not uncommon to encounter ruptured equipment. This usually results when either a small crack propagates rapidly, or the inspection exceeds a specified test pressure.
How does it work?
Hydrostatic pressure tests work by first removing the air in the unit and completely filling the component with water. The component is then pressurized up to 1.5 times the unit’s design pressure limit. The pressure is held for a certain amount of time so that the leaks can be inspected visually. If the pressure lowers, there is a leak somewhere in the system.
You can enhance visual inspection with the help of tracers or fluorescent dyes in the liquid so the originating point of the leaks and cracks can be determined.
When you perform the test on a building’s sanitary sewer system, an inflatable test ball is first inserted in the mainline. The ball is then inflated to block the line. The line is then filled with water up to the slab level, and the water level is observed for the following fifteen minutes. If the water level begins to drop, it proves that there is a leak present.
There are three standard hydrostatic pressure testing techniques used for testing for leaks. These include the water jacket method, the direct expansion method, and the proof testing method.
Let us walk you through the three main methods in detail.
Water Jacket Method
The water jacket method involves filling the vessel with water and then loading it in the test jacket, i.e., a sealed chamber. The water jacket is also filled with water. The container is then subjected to a certain amount of pressure inside the test jacket for a set amount of time.
This allows the vessel to expand inside the sealed chamber, thereby resulting in the water being pushed into a glass tube that measures the total expansion. Once the expansion has been recorded, the vessel is depressurized as it shrinks to its original size. Water flows back into the sealed chamber as the vessel deflates.
Often the vessel does not return to its original size. In such cases, the final size value is recorded as the permanent expansion score. This difference in the reading between the total and permanent expansion helps determine whether the vessel is suitable for work or not.
The higher the expansion percentage, the greater are the chances that the vessel being tested will be withdrawn from service.
Direct Expansion Method
In the direct expansion method, the vessel is filled with a specific quantity of water and pressurized. The amount of water that is expelled after the pressure is released is measured.
The amount of water initially filled into the vessel, the amount of pressure applied, and the amount of water expelled from the vessel is then used to determine the permanent and total expansion scores.
Proof Pressure Method
The proof pressure test works by applying internal pressure, unlike other testing methods. If the vessel being tested has any cracks or leaks or is weak in general due to wall thinness, perhaps, the result will be a failure.
The proof pressure method is only used when the U.S. Code of Federal Regulations does not require recording permanent and total expansion values.
Are there any alternate methods?
Some equipment cannot handle the load required for a hydrostatic pressure test. For this reason, such equipment is tested using alternate methods such as pneumatic testing.
Pneumatic testing is a variant of the pressure test that pressurizes the vessel with gas instead of water. The gases customarily employed for the job are either air or nitrogen.
Particular caution is required for pneumatic testing because gaseous mediums can be easily compressed and must be contained in more copious amounts as compared to conventional hydrostatic pressure testing.
Hydrostatic pressure tests are essential to confirm the presence of any leaks in the plumbing system. They are conducted on pipelines when they are out of service. All oil, gas, etcetera, is vented off and cleaned before the test starts.
Those conducting the test should be mindful of the medium fluid’s properties and its effect on the equipment. We suggest you seek professional help for the job.