Advantages of Using Rupture Discs in Chemical Processes

Protect Your Investments and Personnel: Benefits of Using Rupture Discs Together with Pressure Relief Valves Excessive pressure in production processes can result from a wide variety of causes, ranging from runaway reactions and faulty regulators to operator errors and defective equipment. Excessive pressure not only damages equipment and systems but can also lead to serious consequences, potentially causing personal injury and even loss of life. For this reason, pressure relief valves are widely regarded as a primary safety solution. However, there is sometimes an overlooked aspect: these valves themselves need protection to maintain the desired level of safety. Most pressure relief valves are spring-operated and set to open at a specific pressure. When pressure rises to an unacceptable level, the spring is pushed and the valve opens, releasing the pressure. When pressure returns to normal, the spring forces the valve closed and the process begins again. So why do pressure relief valves need protection? From the product itself. Valves are used in nearly every sector, so there is a wide range of processed products they may be exposed to. Even in environments that appear relatively benign, corrosion, wear and erosion are always a risk because we are dealing with mechanically moving parts. The risks are much higher with more corrosive, adhesive or viscous products. Threats to the operation of pressure relief valves (PRVs) include: • Product buildup, • Corrosion, • Leakage.

Buildup

Product buildup means the risk of blockage or reduction of the orifice. Complete blockage is not the only danger. In many cases, pressure increase is very rapid, so pressure relief must occur at very high volume, high flow rate and high velocity. In this scenario, even a small reduction in the free-flowing orifice means the valve will not be able to relieve pressure efficiently enough, which can cause damage to processing equipment.

Corrosion

Corrosion affecting the PRV, particularly in cases where standard structural materials for pressure relief valves may not be adequate for certain products, must be considered. Corrosion can cause the valve to leak at an increasing rate or prevent it from opening when needed, so it cannot relieve pressure as intended.

Leakage

When leakage occurs, there are two separate issues. First, the small amount of processed product that leaks creates unexpected product buildup on the outlet side, creating the same risks on the inlet side for buildup. Second, there are environmental concerns depending on the product being processed. Emission regulations are becoming stricter worldwide, so leakage can have significant consequences for both the environment and operations if compliance with required limits is not maintained. To reduce risks to PRVs and protect against all these potential threats, a rupture disc can be installed on the inlet side of the pressure relief valve. Rupture discs are proven, non-mechanical devices in the industry that require lower investment and maintenance compared to PRVs. What are the advantages of using a rupture disc together with a pressure relief valve? • Prevention of Leakage, • Corrosion Protection, • Cost Savings, • On-Site Testing Capability, • Elimination of Fugitive Emissions.

Prevention of Leakage

A major advantage of a pressure relief valve isolated from the process via a rupture disc is that it prevents product from leaking to the environment. A typical relief valve will begin to leak as it approaches the set pressure. A rupture disc acts as a solid metal barrier between the process and the PRV. Leakage is becoming increasingly unacceptable globally due to international environmental restrictions or simply to prevent expensive product loss from the system. The process should be able to operate safely without leakage for extended periods, even if it does not contain any toxic or expensive components. Adding a rupture disc to the valve will achieve this. [caption id="attachment_131324" align="aligncenter"] RA type rupture disc (left) and holder/support providing metal-to-metal sealing (right)[/caption]

Protection Against Corrosion

If the sealing surface of the pressure relief valve is exposed to a corrosive product, it can be damaged over time, requiring replacement of even an expensive valve coated with materials such as Hastelloy® or Tantalum. Corrosion can erode alloys and cause the valve to leak or fail to open when needed to relieve pressure. On the other hand, there are metal rupture discs that are completely leak-tight and provide a simple and effective way to isolate the PRV when used on the inlet side. When rupture discs are used in the flow direction of the valve, they will prevent abrasive vapors from contacting the internal parts of the valve. They will also prevent back pressure from affecting the valve's set pressure. Additionally, rupture discs can be equipped with a rupture indicator that signals whether the PRV has opened and is leaking.

Cost Savings

While PRVs have a higher initial investment and must be reusable and periodically maintained, lower-cost rupture discs are single-use. Equipping pressure relief valves with rupture discs allows the use of less expensive materials for the internal parts of the valve, as the need for corrosion protection will be reduced. This combination provides significant cost savings through the following: • Reduced maintenance costs, including calibration, • Less downtime for testing or revision, • Longer service life of the PRV itself, • Reduction in the cost of ownership of the PRV due to use of standard materials for trim parts. PRVs and rupture discs can complement each other, and each offers its own advantages and disadvantages. A parallel or series combination of the two may be the best solution for comprehensive protection of the facility. The combination of discs with PRVs is recognized by API 520 and EN ISO 4126-3 and is used in various industries, including oil and gas, chemical and petrochemical facilities.   [caption id="attachment_131328" align="aligncenter"] Rupture discs and relief valves can be used in parallel (left) and series (right) arrangements.[/caption]

On-Site Testing Capability

The downtime required for inspection and maintenance of PRV spare parts at facilities can be expensive. All of this has an impact on a company's workflow and profitability. Regulations require testing and monitoring to ensure safe system operation. However, with the addition of a rupture disc protection, time-consuming overhauls and the use of expensive spare parts can be prevented. At some facilities, if used alone, PRVs must be removed for off-site testing and maintenance. However, when PRVs are protected by a rupture disc, they can be tested on-site. In particular, by using a reverse-acting rupture disc installed at the valve inlet, the PRV can be tested using a portable pressure source. The space between the valve inlet and the rupture disc can be pressurized until the relief valve opens, thereby verifying the accuracy of the settings.  

Fugitive Emissions

Fugitive emissions are gas or vapor emissions released from pressurized equipment, usually due to leaks from industrial activities and other unintended gas releases. Beyond the economic cost of losses, fugitive emissions contribute to air pollution and climate change. Many countries have strict regulations regarding the monitoring and reduction of these gas emissions. Fugitive emissions also present other risks and hazards. Emissions of volatile organic compounds such as benzene from oil refineries and chemical plants pose a long-term health risk to workers and local communities. In cases where large quantities of flammable liquids and gases are under pressure, leaks also increase the risk of fire and explosion. API 526 standard permits a leakage rate of approximately 40 bubbles per minute or about 170 liters per 24 hours. By adding a rupture disc to PRVs, fugitive emissions are reduced or completely eliminated. Zero emissions during normal operation, no collection and disposal costs, and significant reduction in potential fugitive emission penalties.

Conclusion

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

Hayri Mutluoğlu Electrical-Electronics Engineer Sales Manager Elva Mühendislik