Buckling Pin Relief Valves and bursting discs – Which is best for you?

Buckling Pin Relief Valves (BPRVs) and bursting discs (rupture discs) are used when gas and liquid applications are at risk of becoming over-pressurised in order to relieve pressure. Information from ASME VIII Division I suggests the two are interchangeable — but which is best suited to your application?

BPRFs and bursting discs have developed over the past few decades substantially, yet people are still unsure of them due to past misconceptions. As both BPRVs and rupture discs have full-bore openings when over-pressurised, they offer greater benefits compared to relief valves. Here, rupture disc manufacturer Elfab separates the myth from the facts.

Deterioration over time

In many cases, time is money. Therefore, it is a real worry that BPRVs and rupture discs will fatigue over time — an issue that could potentially lead to increased costs and maintenance time. However, this isn’t the case.

Because they only buckle at a set-point, buckling pins are not subject to process conditions and do not fatigue. Traditional, forward-acting rupture discs were more susceptible to this problem; however, the latest reverse-acting solutions outperform the original designs.

The tolerance rate of many reverse-acting discs is 3% - calculated after being tested over one million life cycles. So, even in the harshest conditions, there is little risk of fatigue. Due to such advanced performance characteristics, some rupture discs are now offered with a 3-year warranty compared to the traditional 12 months.

Performing against a set point

In situations where it is crucial to perform as close to the set point as possible, many people have chosen buckling pins. This is largely driven by concerns around manufacturing, operating, temperature and set point tolerances. 95% to 98% of the set point is usually the maximum operating pressure of modern buckling pins. Where original rupture discs didn't offer such characteristics, reverse-acting discs are available with 3% tolerances and 97% operating ratios. These tighter tolerances mean there is a less dramatic effect on the operation of the rupture disc due to temperature changes. Likewise, in many instances, stock can be rationalised dramatically, reducing purchasing costs.

Concerns over erosion

It is always important that erosion is avoided as it can lead to increased costs and failed investments. For buckling pin relief valves, the pressure relieving part - the pin - is external to the process conditions, meaning relatively cost-effective materials can be used for this component as it will never be in contact with the process media. This ensures low repurchase costs and confidence that the product should not be affected by this problem.

The buckling pin valve is usually created using sourced materials that are known to be compatible with the process medium. While sourcing the valve body in corrosive resistant materials may lead to a high initial investment cost, this is a long-term investment as the valve will typically last the length of the project.

Even though breaking discs do not come into contact with the process medium, they can be created using non-corrosive graphite, hastelloy and tantalum. For modern rupture disc designs, in the instance a rupture disc is affected by corrosion, the discs will be fail-safe, meaning customers will be made aware there is a potential problem.

Leading to a quick review and replacement, when used with modern burst detection systems, users can be easily alerted when a disc fails. In addition, double disc assemblies can be used to allow manufacturing to continue until a suitable maintenance schedule is due to take place.

Ease of installation

Correct installation is essential for equipment to be fully functional in all environments. With many incidences reported by the HSE being related to human factors, it is imperative that manufacturers offer designs that irradiate this issue.

With buckling pins, it is almost impossible to install them incorrectly. Commonly, customers have thought rupture disc designs could be installed incorrectly, however, modern solutions have eradicated this problem. With the introduction of a range of installation tools such as disc alignment tags, flange mounted installation locks (fig. 2) and RFID detection, such occurrences are almost eliminated.

How to know if they are working correctly

To ensure a notification that the product has functioned, it is widely encouraged to incorporate a bust detection system with a pressure relief device. The buckling pin has two conditions, straight and buckled, so it’s clear to see when it has been activated. However, it still relies on an employee noticing this state and doing something about it.

For rupture discs, notification of function is different. Companies cannot solely rely on the fact that they will hear the disc burst; they are therefore encouraged to install burst detection systems. Modern magnetic and reed switch burst detectors are non-invasive to the process and therefore not subject to spurious alarms, back pressures or damage during installation, unlike original designs. Such detectors give an instantaneous notification of a burst, and can even be wired to a control room to shut down a process as a further safety measure.

With multiple benefits, it eliminates a decrease in production time and capabilities. Secondly, by stopping the process it ensures that no dangerous gases are leaking into the environment. Thirdly, it enhances overall safety.

Maintenance expenses

Often, the regular and routine maintenance required for a device is outlined in the company’s quality manual. Reducing and improving maintenance schedules plays a critical part in improving site efficiencies.

A benefit of buckling pins is that they are largely maintenance-free and can be inspected without disrupting the line. Replacement pins can also be installed in a matter of minutes without breaking the line.

Contrasting this are bursting discs which must be removed from the holder to be inspected. However, installation tools’ quick and simple checks of the rupture disc state mean this can be done without stopping the line, making the maintenance of both solutions equally as rapid and as environmentally friendly.Some rupture discs now come with a standard three-year warranty, increasing maintenance intervals accordingly.

Which device should you choose?

Before making a decision, line-size, initial investment and long-term investment should all be considered. As modern day designs offer comparable performance characteristics, considerations based on an application would make for a better decision-making process, rather than worrying about these common misconceptions that on the whole have been eradicated through continued advancements.

Author profile:
Laura Jane-Todd is an engineering copywriter, writing on behalf of Elfab

Laura Jane-Todd

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