What is hydrotest pressure and how to calculate the hydrotest pressure

Hydrotest  pressure is the technique in which pipes, pressure vessels, gas cylinders, tanks are tested  at required design pressure of the system or pipes or vessel to check the leak and strength.

Hydrotest pressure is the pressure used to test the strength and integrity of a pressure vessel or piping system. It is typically 1.5 times the design pressure of the system, but it can be higher depending on the specific requirements. The test pressure is applied for a period of time, typically 2 hours, to allow for any leaks to develop.

 

There are a few reasons why the hydrotest pressure is usually 1.5 times the design pressure. First, it helps make sure that the system can handle sudden pressure spikes. Second, it helps get rid of any flaws in the material that wouldn’t show up at the design pressure. Third, it helps pre-stress the material, which can improve its wear life.

Hydrotest pressure is an important part of making sure that pressure tanks and piping systems are safe and reliable. It helps to make sure that the system can handle the pressures it is meant to work at, and it helps to find any flaws that could cause it to fail.

1  Hydrotest pressure is 1.5 Times of Design Pressure.

2. For a design temperature above the test temperature, minimum test pressure can be calculated as:

Pt = (1.5 X P X St) / S

Pt : Minimum Test Pressure.

P : Internal design pressure.

St: Allowable stress at test temperature.

S : Allowable stress as design temperature.

3. If a test pressure as per above would produce a stress in excess of the yield strength at test temp. the test pressure may be reduced to maximum pressure that will not exceed the yield strength at test temp.

4. If the test pressure of piping exceeds the vessel pressure and it is not considered practicable to isolate piping from vessel, the piping and vessel may be tested together at test pressure of the vessel when approved by owner and provided the test pressure for vessel is not less than 115% of piping design pressure adjusted for temperature as per point no.2.

Fittings to remove while performing the hydrotest pressure

When doing a hydrotest pressure test on a pipe system, there are certain pipe fittings that need to be removed. The reason for this is to keep the test safe and make sure it works properly.

• Valves: Those little things you use to turn the flow on and off. They could get damaged or cause problems during the test, so we take them out.

• Gauges: The pressure gauges that show how much pressure is in the pipe. They might not handle the test pressure, and we don’t want them to break or give wrong readings.

• Pressure Regulators: These helps control the pressure in the system, but they’re not built for the high pressures of the test. So, we remove them temporarily.

• Expansion Joints: These are used to deal with pipe movement when it gets hot or cold. But they’re not strong enough for high test pressures, so we take them out for now.

• Flexible Hoses: Any temporary hoses used during construction or maintenance could get damaged during the test, so we remove them to be safe.
• Strainers and Filters: These are meant to catch debris, but they might get clogged or damaged during the test, so we remove them too.
• Orifice Plates and Flow Restriction Devices: These can create pressure points and mess up the test, so we take them out for the test period.

By removing these fittings before the test, we reduce the risk of damage and can make sure the pipe can handle the pressure safely. The whole point of the test is to find any leaks or weaknesses, so we want to make sure it’s done right. Always follow the rules and safety guidelines when doing any pressure tests to keep everyone and everything safe.

The hydro test pressure is typically 1.5 times the design pressure for a pressure vessel or piping system. This ensures the vessel or system can withstand the maximum pressure it is designed to operate at, plus an additional
safety factor. The extra pressure also helps identify potential leaks or weak spots in the vessel or system.

Reasons why hydrotest pressure is 1.5 times

• To ensure the vessel or system can withstand the maximum pressure it is designed to operate at.

• To provide a safety factor if the vessel or system is subjected to higher-than-expected pressures.

• To identify any potential leaks or weak spots in the vessel or system.

• To verify the quality of the welds and other fabrication methods used to construct the vessel or system.

• Ensure that the vessel or system is properly cleaned and free of contaminants.

The hydro test pressure is normally specified by the relevant code or standard. The hydro test pressure for pressure vessels must be at least 1.5 times the design pressure, according to Section VIII, Division 1 of the ASME
Boiler and Pressure Vessel Code.

It is crucial to remember that the hydro test pressure shouldn’t be higher than the vessel or system’s maximum permissible working pressure (MAWP). The MAWP is the highest pressure that a vessel or system can sustain safely while operating. Overriding the MAWP may cause system or vessel damage and failure.

Benefits of hydrostatic pressure testing

• It can help to find leaks in the system.
• It can help make sure that the system can handle the planned pressure.
• It can help improve the fatigue life of the machine.
• It can help remove any flaws in the material.

Hydrostatic testing is a normal process for pressure vessels and piping systems. It is an important part of making sure these devices are safe and reliable.