Rupture discs + Safety Valves Wiki

By definition, safety valves, like rupture discs, are pieces of equipment with a safety function. They are used to protect containers and piping systems from impermissible overpressure. This is done by the safety valve enabling targeted pressure relief. If the pressure inside a boiler or pipe exceeds a certain limit value, the safety valve opens and thus prevents further pressure build-up. A wide variety of designs exist, with spring-loaded systems making up the majority of the systems used today.

A closing force can be generated on the sealing surface by spring tension. If the back pressure exerted by the process medium on the closing geometry is sufficiently large, the spring is compressed and releases a certain cross-section for relief. If the pressure drops sufficiently, the spring force dominates and the valve closes. A safety valve is therefore, unlike a rupture disc, a reusable pressure relief device that, for mechanical reasons, must be subjected to regular checks.

Every operator who has ever been in this position knows the problem: The functionality and reliability of some safety equipment is affected to a greater or lesser degree by corrosive, adhesive, polymerising or viscous media.

This also applies to safety valves. If the valve seat is sticky, it is no longer possible to guarantee the defined response pressure. This poses a risk even before the first time the safety valve is triggered. Cleaning and inspections are therefore essential toguarantee that – in the case of an emergency – the safety valve responds at the specified pressure. A REMBE^® rupture disc installed upstream protects the safety valve against caking and adhesions. Reverse acting rupture discs like KUB^® have a smooth metal surface on the side facing the process, which prevents the build of deposits. Breaking points are isolated from the process. This ensures that the specified response pressure is maintained at all times and eliminates the possibility of a late response.

There are a number of industrial processes in which the use of pressure relief devices is unavoidable. Boilers and reactors, pipes and pipelines, pumps and compressors as well as cooling and heating circuits are protected with safety valves. Impermissible overpressure can occur in these processes for a variety of reasons. This can result in external fire, chemical reaction, failure of cooling or heating systems, thermal expansion of the process fluid, and blocked drains. For the selection of a suitable pressure relief device, it is always relevant how quickly the pressure rises and which volume flows are to be discharged during the relief. With knowledge of the process conditions and medium, safety valves that are particularly suitable for the application at hand can be selected. Characteristic parameters of a safety valve are response and closing pressure, the smallest opening diameter, the coefficient of discharge and the valve's lift/pressure dependency.

Historically, safety valves were also used to regulate the working pressure, for example in steam locomotives, in their early days. Today, however, the sole task of the safety valve is to protect processes, people and the environment against the consequences of uncontrolled pressure relief, in the worst case in the form of an explosion. Although users nowadays also have a wide range of other protective technologies in the form of control circuits, control devices and process monitoring devices available, safety valves are still generally used as a fail-safe final safeguard to ensure safe pressure relief even if the aforementioned instruments fail. They must therefore always reliably open at a certain pressure level in order to prevent a further increase in pressure and should close completely again after successful pressure relief in order to prevent further emissions and product loss.

Safety valves are pieces of equipment with a safety function, which is why their full functionality must be permanently ensured. Adequate protection is only available if the safety valve opens reliably and also closes again automatically. Incorrect installation and poor maintenance are the causes that contribute significantly to the failure of safety valves. Special attention is therefore required both during assembly and during maintenance of this safety device. In particular, routine maintenance intervals help to extend the service life of safety valves and ensure correct functionality. It is recommended that these checks be performed every 6 to 12 months. In a visual inspection, the valve should be checked for intact seal wires and signs of corrosion and leakage.

Rupture discs, like safety valves, are pieces of equipment with a safety function that can be used to relieve pressure in vessels and pipes. They can be used alone, in parallel or in series with safety valves. If safety valves and rupture discs are combined, the aim is always to add the advantageous properties of the individual components. In parallel with safety valves, rupture discs are used in particular when a safety valve tends to fail due to the application or when it must be expected that there will be unusually high or very rapidly increasing pressure peaks in the process, which cannot be adequately relieved by a safety valve. In series, rupture discs and safety valves are mainly used when particularly corrosive, sticky or toxic media have to be relieved.

Normally, safety valves have to be removed in order to test whether they are functioning correctly. This is time-consuming and expensive. However, in combination with REMBE^® rupture discs, you can test your safety valves without moving them anywhere. To do this, the space between the rupture disc and the valve stroke is pressurised.

As KUB^® has a back pressure resistance of 135 %, the rupture disc remains undamaged while the safety valve is being inspected. If in-house regulations nonetheless require the safety valve to be removed for inspection, the rupture disc can be left in position in a separate flange connection in order to close the opening while this work is being performed.

The combination of safety valve and rupture disc results in unique advantages. In this way, the series connection enables greater tightness without sacrificing the advantage of resealability. The rupture disc guarantees the technical tightness, while the safety valve closes the container again even after the pressure has been successfully relieved. By isolating the safety valve from the process medium, it can also be ensured that the valve seat does not stick or that the leakage rates do not increase due to corrosive processes. If reverse rupture discs are used, which usually have a particularly high reverse pressure resistance, it is also possible to apply pressure to the intermediate space of the combination. This enables the safety valve to be subjected to an in-situ function test, which significantly reduces the maintenance and testing costs of the safety valve.