Often, Buckling Pin Relief Valves (BPRVs) and rupture discs are seen as being interchangeable. They both offer full-bore opening when over-pressurised, helping to protect against the over-pressurisation of applications.
There are many misconceptions around the two. In this article, Elfab dispels the most common misconceptions to help you decide which solution is best for your application.
Fatigue is a key concern, as many believe it will lead to increased costs and maintenance. However, buckling pins do not fatigue, as they are not subject to process conditions and buckle only at their set point. Traditional, forward-acting rupture discs were more susceptible to this problem, however, the latest reverse-acting solutions outperform the original designs.
Tested to over one million life cycles and benefitting from 3% tolerances, modern reverse-acting rupture discs have little risk of fatigue even in harsh 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.
Driven by manufacturing, operating, temperature and set point tolerances, many have chosen BPRVs to allow them to operate as close to the set point as possible.
95% to 98% of the set point is typically the maximum operating pressure offered by 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.
Corrosion is to be avoided to prevent investments failing and long-term costs from increasing. 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.
Carbon or stainless steel are usually used for the buckling pin valve itself, as they are normally 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.
Bursting disc devices are usually made from non-corrosive materials, such as 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. To allow for the quick review and change out of rupture discs in the event of corrosion, it is recommended that they are used in combination with modern burst detection systems to trigger an instantaneous alert. In addition, double disc assemblies can be used to allow manufacturing to continue until a suitable maintenance schedule is due to take place.
Of course, each device needs to be properly installed in order to deliver the correct levels of safety and performance. With many incidences reported by the HSE being related to human factors, it is imperative that manufacturers offer designs that irradiate this issue.
It is very difficult to install a buckling pin 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 and RFID detection, such occurrences are almost eliminated.
A burst detection system is widely encouraged by a number of manufacturers. This is the only safe and reliable way to get a notification that the product has functioned.
You can clearly see 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.
There is no guarantee that an employee will hear a rupture disc burst, so installing burst detection is encouraged. 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 key benefit of doing so is that it allows you to resume processes and avoid losing valuable production time. Secondly, by stopping the process it ensures that no dangerous gases are leaking into the environment. Thirdly, it enhances overall safety.
High maintenance costs
Usually, regular and routine maintenance is carried out in accordance with a company’s quality manual. Reducing and improving maintenance schedules plays a critical part in improving site efficiencies.
BPRVs are largely maintenance-free and can be inspected without breaking the line. Replacement pins can also be installed in a matter of minutes without disrupting the line.
A rupture disc needs to be removed from a holder before its state can be checked. However, the introduction of installation tools quick and simple checks of the rupture disc state 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 3-year warranty, increasing maintenance intervals accordingly.
Making a decision
Now you better understand each device, which one should you choose for your application? Considerations should be made on 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.Author: Autumn Wiberg
Read the article online at: https://www.worldpipelines.com/special-reports/23012018/what-is-the-difference-between-bprvs-and-rupture-discs/
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