What a Pressure Test Is and Why It Is Done
The purpose of a pressure test, the occasions that need one, and what this awareness course does and does not qualify you to do.
11 min
Activities: 0 of 3
A pipe, a vessel or a pipeline is built to hold a fluid at pressure for many years. Before it does that, somebody must prove that it can. A pressure test is that proof. The system is closed, filled with a test fluid and brought to a set pressure for a set time, while people watch for leaks, for movement and for any loss of pressure.
Two questions can be asked by a test. The first is strength: will the system hold a pressure above the one it was designed for, without breaking or deforming? The second is tightness: will the joints, seals and welds hold the fluid in, with no leak? Some tests answer both questions. Others answer only the second one.
When a pressure test is needed
The paradox of the test
A test is done to find weakness. If a system has a bad weld, a wrong gasket or a closure that is not rated for the pressure, the test is the moment when it fails. That is the purpose: it is far better for a weak point to fail with water inside and nobody near it than with hydrocarbon inside and a crew working beside it.
So every test must be planned as if the system will fail. The question is never "will it hold?" but "if it does not hold, who and what is in the way?" A team that expects the test to pass and stands close to watch has forgotten why the test is being done.
Match the occasion to the reason for the test
Match each situation on the left with the reason for testing on the right.
- A new process line before commissioning
- A flange remade after maintenance
- A section of pipe replaced after corrosion
- A vessel given a higher design pressure
A test supervisor says: "This line was welded by our best welders, so it will pass. We can stand next to it to watch." What is wrong with this thinking?