Safety valves and burst discs?

You can check relevant materials to find out when to use safety valves, when to use rupture discs, and in what situations both are used, as well as whether they should be used in series or in parallel. It is described in some information on safety accessories

Take a look at http://bbs.hcbbs.com/viewthread.php?tid=193700. Emergency relief valves are generally used on storage tanks at atmospheric pressure; the substances contained in such tanks can usually be allowed to escape in small amounts. In other words, these substances are either non-toxic or have low toxicity. If the substances are toxic, then rupture disks must be used, or the inlet and outlet pipes must be connected together so that the toxic substances can be collected. Blowout valves and safety valves are used on pressure vessels; blowout valves are generally employed when the pressure is less than one kilogram or when very high pressures are present, while safety valves are used in other cases. If the medium is toxic, it will pollute the environment, and a burst disc safety valve may need to be used in series.

Refer to: HGT20570.3-95 – Setting and Selection of Burst Discs; HGT20570.2-95 – Setting and Selection of Safety Valves

Article 142 of the Code stipulates that when a safety valve cannot operate reliably, a burst disc device shall be installed, or a structure combining a burst disc device with a safety valve device shall be used. When a composite structure is used, the relevant provisions of Appendix B to GBl50 shall be complied with. Any burst disc connected in a composite structure must not generate fragments when it activates. In practice, however, it is rare to see safety valves and burst discs used together, and even in situations with complex operating conditions, their combined use is uncommon. Now, the parts of rupture disks and safety valves that come into contact with the medium, such as the valve bodies and seals, can all be made from special materials. Personally, I think: there’s no need to use both at the same time.

What is the practical significance of using the two in parallel? ? How about series connection? This post was last edited by cyl2005 on 2008-7-23 23:01.]

The function of a safety relief device is to prevent the container from overpressuring and to ensure normal operation. A safety valve is a safety discharge device that can be used multiple times and opens and closes automatically as pressure changes. Blowout discs are designed for single-use; a new one must be replaced after each overpressure event or failure. Usually, when a safety valve cannot operate reliably, a burst disc is installed, or both a safety valve and a burst disc are used simultaneously. In addition, pressure relief via a burst disc must be used in the following situations: 1. The material inside the container could cause the safety valve to fail ； 2. Containers that must not allow any material leakage during normal operation ； 3. The pressure inside the container increases too rapidly, and the pressure relief speed of the safety valve is not sufficient ； Other situations in which the safety valve cannot function properly.

I. Application scope of rupture discs: 1. The medium inside the container tends to crystallize or polymerize； 2. Chemical reactions make it difficult to control safety valves ； 3. The medium is extremely or highly hazardous, making it difficult for safety valves to meet the requirements ； 4. Ultra-high pressure, with an extremely low likelihood of release. II. The burst disc can be located at the inlet or the outlet of the safety valve.

Under what circumstances is a burst disc installed at the outlet of a safety valve?

I believe that when used in parallel, the operating conditions must meet the requirements of both devices. Additionally, the setting pressure of the safety valve can be set lower than the specified burst pressure of the rupture disc; in other words, usually the safety valve will activate before the rupture disc bursts. Only when the pressure continues to rise and reaches the burst pressure of the rupture disc will it be the latter that releases pressure. This can reduce losses. When operating in series, leakage can be prevented during normal operation ； It also enables the pressure relief device to return to its original position automatically after activation, thereby reducing losses as well. The above views are for reference only; please point out any inaccuracies. This post was last edited by Smoke from a stove in the desert on 2008-7-24 08:59.]

Correct. But the operating condition during series connection wasn’t explained clearly upstairs. When the pressure is stable, neither the series-connected safety valve nor the burst disc operates ； In the event of overpressure, if the set pressure of the safety valve is lower than the burst pressure of the rupture disc, it will activate first to relieve pressure ； If the overpressure remains severe at this point, or if the pressure relief rate of the safety valve is insufficient, the burst disc will activate and the pressure will drop rapidly ； If the pressure inside the container returns to normal at this point, the safety valve reseats, achieving a sealed condition. Using this time, the burst disc can be replaced online. .

I understand the case of parallel use, but I’m still not quite clear about series connection? Looking forward to a detailed explanation, thanks!

Can your explanation be understood in this way? The rupture disc is installed behind the safety valve; when the safety valve opens, the pressure in front of the valve is released into the pipe between the rupture disc and the safety valve. So does this pipeline need to be designed to be quite long or quite thick in order to meet the pressure relief requirements? Otherwise, would the overpressure rupture disc have to explode every time? Thank you! This post was last edited by cyl2005 on 2008-7-25 15:53]

In the case of particles, a filtering device should be installed before the inlet of the safety valve； When installation is required but it is not suitable, a burst disc should be installed or a burst disc used in series with a safety valve. Why does a container experience overpressure under normal operation? 1. Pressure in pressure vessels comes from external sources; if the amount of gas entering the vessel is greater than the amount exiting, the density increases and thus the pressure rises ； 2. Pressure relief valve failure ； 3. The medium undergoes chemical reactions, causing the pressure to keep rising (due to improper material handling, etc.) ； 4. Containing liquefied gases, with rising operating temperature or overfilling ； 5. The storage medium undergoes polymerization reactions, resulting in an increase in heat and pressure. 6. In high-pressure reactors used for manufacturing polymer compounds, improper use of raw materials or catalysts, or operational errors can lead to the explosive polymerization of monomers, causing a sharp rise in heat and thus a sudden increase in pressure. I. Safety valves must be installed in the following pressure systems: a) When the pressure in a container comes from a system without a safety valve ； b) Pressure vessels or pipelines with a design pressure lower than that at the source ； Pipes at the outlets of positive displacement pumps and compressors ； c) Vessels subjected to overpressure due to the accumulation of non-condensable gases ； d) Liquefied gas storage tank ； e) Auxiliary storage tank of the air compressor ； f) Pressure vessels in which exothermic reactions or chemical reactions take place, resulting in an increase in gas pressure ； g) Polymerization (physical reaction) equipment ； h) Heat exchanger with a heat carrier for heating and vaporizing the liquid inside the vessel ； i) Those in which the pressure is reduced using a pressure regulator before being fed into the container (containers that operate at a pressure lower than that of the pressure source); j) Waste heat boilers ； k) Pressure vessels with highly toxic media that pose an extreme hazard ； l) Containers and the like that share the same gas source. II. The following pressure systems are not suitable for installing safety valves: a) Systems where the pressure may rise rapidly, such as in cases of chemical explosions; b) Systems in which the fluid being discharged contains particles, is prone to deposition, crystallization, polymerization, or has high viscosity ； Highly corrosive media ； c) Some situations where factors such as an excessively large discharge area of the safety valve, high cost, and difficulty in operation occur (such as extremely low temperatures)

I. Principles for installing safety relief devices Safety relief devices must be installed in any of the following situations. (1) On containers whose pressure source is at or may be above the maximum allowable operating pressure of the container. (2) On containers where physical or chemical changes in the working medium may cause the internal pressure to exceed the maximum allowable operating pressure. (3) On containers holding compressed gases or liquefied gases. (4) Heating and evaporation, as well as heat exchange processes, can cause the pressure in containers to exceed the maximum allowable operating pressure. (5) On fluid hydraulic equipment where the pressure may exceed the maximum allowable operating pressure. (6) Containers without safety valves at the source of pressure. II. Performance of safety valves and burst discs 1. Safety valve: It reduces the excessive pressure inside by automatically opening to release gas. (1) Advantages: It only releases the pressure in the pressure vessel that is above the specified level; once the pressure inside the vessel drops to the normal operating level, it shuts off automatically. This prevents waste and production disruptions that would occur if all the gas had to be released in case of overpressure in the vessel. The device itself can be reused multiple times, and its installation and adjustment are also relatively easy. (2) Disadvantages: The sealing performance is poor; even compliant safety valves may experience slight leakage under normal operating pressure ； Due to the inertia of springs and similar components, there is a delay in the opening of the valve, resulting in a slow pressure relief response. Furthermore, when safety valves are used with impure gases, there is a possibility of blockages inside the valve and the valve disc sticking. (3) Scope of application: Suitable for equipment handling relatively clean gases such as air and water vapor; not suitable for equipment dealing with toxic media ； It must not be used in equipment where intense chemical reactions may occur, leading to a sudden increase in pressure. (4) When selecting a safety valve, its discharge capacity must be greater than the equipment’s safe discharge volume. The type of safety valve is selected based on the process conditions of the equipment and the properties of the working medium, with an appropriate safety valve being chosen according to the maximum allowable operating pressure. Note: The safe discharge volume of a pressure vessel refers to the amount of gas that must be discharged per unit time when the vessel is under overpressure, in order to prevent its pressure from rising any further. The discharge capacity of a safety valve refers to the amount of fluid discharged per unit time at the discharge pressure when the valve is in its fully open position. 2. Blown valves: These utilize a bursting element that breaks under high pressure to release gas (wherein blown valves are commonly used in medium and low-pressure containers, while burst discs are used in ultra-high-pressure containers). (1) Advantages: Good sealing performance, with no leakage when the container is operating normally ； The rupture speed of the blast disc is high, so the pressure relief reaction is rapid ； The presence of contaminants such as oil in the medium does not affect the operating pressure of the device components. (2) Disadvantage: After completing the pressure relief action, the blasting element can no longer be used, and the container must be forced to stop operating once it experiences overpressure ； Blasting elements are under high stress for extended periods, making them prone to premature failure due to fatigue; as a result, their lifespan is short and they need to be replaced regularly. Furthermore, the operating pressure of the blasting element is also difficult to predict accurately and control strictly. (3) Scope of application: It is suitable for containers where rapid pressure increases may occur during chemical reactions, or those containing highly toxic substances; it is not suitable for liquefied gas storage tanks. It is also not suitable for containers with large pressure fluctuations, i.e., those that experience frequent overpressures. 3. Safety valve-bleed valve combination device: This pressure relief device, formed by combining a safety valve and a bleed valve, possesses the advantages of both valve-type and rupture-type mechanisms. It prevents leakage that would occur if only a safety valve were used, and it also allows the container to be reused after releasing excessive pressure. The rupture disc of the combined device can be installed on the inlet or outlet side of the safety valve, depending on the specific requirements. In the former case, a rupture disc can be used to isolate the safety valve from the gas inside the vessel, thereby preventing the safety valve from being corroded or clogged or stuck by impurities in the gas. When the pressure in the vessel exceeds a certain level, the rupture disc breaks, and the safety valve opens as well. Once the pressure in the vessel drops, the safety valve closes again, allowing the vessel to continue operating temporarily; the rupture disc can then be reinstalled once the equipment is shut down for maintenance. This design requires that the rupture of the burst disc not interfere with the proper operation of the safety valve, and it also demands that a checking device be installed between the burst disc and the safety valve to prevent pressure from building up between them and affecting the proper functioning of the burst disc. When the rupture disc is installed on the outlet side of the safety valve, it protects the disc from fatigue damage caused by long-term exposure to gas pressure and temperature; the rupture disc serves to remedy leaks in the safety valve. This structure requires the gas between the burst disc and the safety valve to be discharged promptly; otherwise, the safety valve will lose its functionality. Combined structural safety pressure relief devices are generally used for containers holding corrosive liquefied gases, or highly toxic and rare gases. Due to the hysteresis effect of the safety valve in the device, it cannot be used in reaction vessels where the pressure rise rate is extremely high.

The cascaded use of safety valves and rupture discs has the following advantages: 1. It achieves zero emissions to the atmosphere; 2. It extends the interval between major overhauls; 3. The safety valves can be calibrated on-site 4. It can save precious metals——reducing costs. 5. The burst disc in front of the safety valve separates it from corrosive substances, thereby extending the service life of the safety valve.

In what situations or conditions are rupture discs needed, and when are safety valves required?

Safety valves will always leak. The burst disc is properly sealed; I know of a Fike one that’s good

A lot has already been said in great detail about the combination of burst discs and safety valves, so I don’t want to go into further detail here. LZ’s idea is correct; one of the advantages of using rupture discs to isolate safety valves is that it avoids the need to use expensive, high-quality models for these valves, as ordinary rupture discs can suffice, thereby saving a significant amount of money. Another cost savings provided by isolated safety valves is the ability to conduct annual inspections of these valves online, without the need to stop production for such inspections; this ensures continuous operation and is also an advantage in terms of cost reduction.

Hahaha, learned a lot more here, thanks:lol

When a safety valve cannot operate reliably, a burst disc device should be installed; the burst disc must not produce fragments when it activates