Isolation of Pressure Relief Valves from Inlet Side

Excessive pressure in production processes can be the result of a variety of causes, from leak reactions and faulty regulators to operator errors and faulty equipment. Excessive pressure can have serious consequences, not only damaging equipment and systems, but also potentially leading to personal injury or even loss of life.

For this reason, pressure relief valves are widely viewed as the primary safety solution. However, what can sometimes be overlooked is that these valves themselves also need protection in order to maintain the desired level of safety.

Most pressure relief valves are spring loaded and are set to open at a certain pressure. When the pressure rises to an unacceptable level, the spring is pushed open and the pressure is released. When the pressure level returns to normal, the spring forces the valve to close and the process begins again.

So what do pressure relief valves need protection from? From the product itself. Valves are used in almost every industry, so there is a wide variety of processed products to which they may be exposed. Even where the environment looks relatively good, corrosion and wear and tear are always a risk because we are dealing with mechanical moving parts. The risks are much higher with more abrasive, sticky or viscous products.

The three main problems that can affect PRVs are: Product buildup inside pressure relief valves, corrosion, and leakage.

Accumulation

Accumulation of product means risk of clogging or reduction of the orifice. Complete blockage is not the only danger. In many cases, the pressure increase is very rapid, so the pressure relief must be at a very high flow rate and high speed with a high volume. In this scenario, even a small reduction in the free-flow orifice means that the valve will not be able to relieve pressure efficiently enough, resulting in damage to the processing equipment.

Corrosion

Corrosion affecting the PRV needs to be considered in relation to specific products, especially where non-standard materials of construction may be required for the pressure relief valve. Corrosion can cause the valve to leak at an increased rate or fail to lift when required, so it cannot relieve pressure as desired.

Fugitive

When it comes to leakage, there are two separate problems. First of all, a small amount of processed product leaking can lead to an unexpected accumulation of product on the outlet side, posing the same risks identified for accumulation on the inlet side. Secondly, there are environmental concerns depending on the product being processed. Emission regulations are becoming stricter around the world, so leakage can have significant consequences for both the environment and the business if it does not comply with the required limits.

To protect against all these accumulation, corrosion and leakage problems; A burst disc can be placed on the inlet side of the pressure relief valve.

Protection Against Accumulation

Using a rupture disc, the pressure relief valve is closed and contact with the product is prevented. Discs are designed to have no gaps or cracks where product can stick or accumulate, unlike the typical edges and angles found in a valve port design. If there is excessive pressure, the discs burst, allowing the relief valve to operate as intended without any rupture. Once the pressure is relieved, the valve closes the system again and the discs can be replaced at a convenient time. This results in a reduced downtime if used whereas if the rupture disc were not used to protect the valves you would have to clean and maintain the valves regularly.

Protection Against Corrosion

Not only does a rupture disc prevent the product from corroding the internal parts of the valve, it also means it is cost-effective to achieve chemical compatibility when special construction materials are required. By using a burst disc made of durable alloy on the inlet side, the pressure relief valve can be made from lower cost material, meaning construction costs are reduced without any loss of reliability in the pressure safety system.

Protection Against Leakage

Rupture discs will completely prevent leakage. This means the maintenance required by pressure relief valves is significantly reduced. Additionally, when normal valve set pressure testing is required, this can be done on-site. The space between the valve inlet and the rupture disc can be pressurized in situ until the relief valve opens, eliminating disassembly for laboratory testing and the resulting downtime. The rupture disk provides a back pressure margin to avoid being affected by such tests.

Conclusion

The use of burst discs at the inlet of pressure relief valves will improve the selected level of pressure relief and reduce the need for cleaning, maintenance and repair. Corrosion problems and downtime costs on both the inlet and outlet side of the pressure relief valve can be significantly reduced for better efficiency of the production site. Finally, by adding rupture discs to the inlet of the pressure relief valve, higher process safety is achieved in a plant with a low cost of ownership.