Both rupture discs and Buckling Pin Relief Valves (BPRVs) are primary pressure relief devices, working to protect against the over-pressurisation of applications. Many believe they are interchangeable but, while similar, it’s important to make the best choice for your application. Bursting disc manufacturer Elfab explains more to dispel the misconceptions:
Fatigue over time
It’s a common worry that BPRVs and rupture discs will fatigue, leading to increase replacement and maintenance costs. However, this isn’t strictly true.
As they only buckle at a set point and are outside of process conditions, buckling pins 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 majority of reverse-acting discs have 3% tolerances tests over one million life cycles. This means the risk of fatigue is low in event the harshest operating conditions. Due to such advanced performance characteristics, some rupture discs are now offered with a 3-year warranty compared to the traditional 12 months.
Largely driven by concerns around manufacturing, operating, temperature and set point tolerances, many choose buckling pins when they need to operate close to a set point. Typically, modern buckling pins offer maximum operating pressures of 95% to 98% of the set point.
Now, reverse-acting discs can operate 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.
To prevent early failure and additional costs, preventing corrosion is a key concern for those considering rupture discs and BPRVs. 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.
BPRVs are usually created using a compatible material to the process medium, like carbon or stainless steel. 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.
Likewise, rupture discs are manufactured from a number of non-corrosive materials, like graphite, hastelloy and tantalum. For modern rupture disc designs, in the instance a rupture disc is affected by corrosion, the discs will fail-safe, meaning customers will be made aware there is a potential problem.
It is recommended that discs are used alongside modern burst detection systems. This ensures that if a disc does fail as a result of corrosion, an alert will sound and the disc can be reviews and changed quickly. In addition, double disc assemblies can be used to allow manufacturing to continue until a suitable maintenance schedule is due to take place.
Where safety is critical, the correct installation of these devices is vital. With many incidences reported by the HSE being related to human factors, it is imperative that manufacturers offer designs that irradiate this issue.
BPRVs are impossible to wrongly install. 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 and RFID detection, such occurrences are almost eliminated.
Burst detection systems are widely encouraged by most manufacturers. This is the only safe and reliable way to get a notification that the product has functioned.
It’s clear when a buckling pin has been activated, as it only has two conditions; straight and buckled. However, it still relies on an employee noticing this state and doing something about it.
You can’t rely on the fact you will hear a rupture disc burst, underlining the importance of burst detection. 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.
One of the key advantages of doing so is that it allows the customer to get a process up and running quickly to avoid lost production. Secondly, by stopping the process it ensures that no dangerous gases are leaking into the environment. Thirdly, it enhances overall safety.
The cost of maintenance
Regular and routine maintenance is usually carried out in-line with a company’s quality manual. Reducing and improving maintenance schedules plays a critical part in improving site efficiencies.
BPRVs can be inspected without breaking the line, so are generally maintenance free. Replacement pins can also be installed in a matter of minutes without disrupting the line.
Installation tools make it easy to check the state of a rupture disc without stopping the line. The maintenance of both solutions equally as rapid and as environmentally friendly. Some rupture discs now come with a standard 3-year warranty, increasing maintenance intervals accordingly.
Which solution to choose?
When considering which solution to choose, examine the size of the line and initial investment versus long-term investment. 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.