FIKE brand rupture discs are an excellent solution for the protection of pressurized equipment such as kettles, tanks, reactors, autoclaves, etc. Its proper functioning depends on how well you know how to choose the disc for each application. Temperature, pressure and fluid are basic variables for choosing a rupture disc, but there are other variables that will help a disc last longer and not cause damage to the facilities.
The following are the variables that allow you to choose a wide range of rupture discs from the FIKE brand, a company with more than 65 years of experience in the manufacturing and marketing of these elements. Understanding 22 basic questions will be the key to success when choosing the optimal rupture disc.
1. What is the required number of rupture discs?
The more rupture discs needed, the less cost it will have; For each batch of discs that the client needs, three more must be manufactured to be able to exploit them at the pressure and temperature required by the client. The explosion pressure result of each rupture disc is averaged and the average is recorded in each batch to be shipped to the customer. The cost of the three exploited disks is charged to the rest of the disks to be shipped, therefore it is much more economical to purchase seven disks than to buy just one. In other words, in cost, five costs less than four, four costs less than three, and so on.
2. What is the type of rupture disc required?
It turns out that FIKE handles more than 13 types of rupture discs, the choice of the disc is provided by a FIKE line specialist who has the knowledge and expertise to know what to offer and not the client, unless the client orders it with a specific lot #. However, the client’s request is ALWAYS evaluated. The difference between discs depends on the size range, burst pressure range, operating radius, whether fragmentable or not, whether it is vacuum resistant or not, whether it is cyclic or not, the process medium, the installation location and the connection type.
3. What should be the size of the rupture disc?
The size or dimension of the nominal diameter (DN) is given exclusively by the client, unless the query to FIKE is extrapolated to determine its nominal diameter (DN). Each piece of equipment is unique and the size of a disk must be designed by the equipment manufacturer to evacuate the energy in the event of a given relief. The sizing of the disc must be based on the ASME (American Society of Mechanical Engineers) Section VIII Division 1 standard, which expresses the protection guidelines that pressurized equipment must have in an industrial process.
4. What is the type of material for each component of the rupture disc?
The material must be given by the client and depends on the compatibility with the fluid to be worked in the process, the most conventional material is 316 L stainless steel due to its low carbon component that makes it compatible with most products in the industry, other materials such as Nickel, Monel, Titanium, among others, are available but are more expensive and scarce.
5) Is any protective layer, inliner or coating necessary between the rupture disc and the process?
Yes, with industrial technological advances, there are products on the market to help prevent corrosion between materials, extending the useful life of the discs. This coating is placed under the disc and consists of a very thin film that will be between the process and the disc, avoiding direct contact of the metallic material and the process.
Below is a range of inliners on FIKE rupture discs:
- POLYURETHANE 250°F (121°C).
- PTFE from -20 °F to 450 °F (-28 °C to 232 °C) polytetrafluoroethylene, it is inert industrial anticorrosive applications.
- PFA -40°F to 500°F (-40°C to 260°C) PERFLUOROALKOXIDE is an evolved PTFE.
- FEP from -40 °F to 400 °F (from -40 °C to 204 °C) fluorinated ethylene propylene, like PTFE, retains almost all the properties of interest in these polymers: very high chemical inertness, very high dielectric strength, very low surface energy, allows contact with food and very high processability.
On the other hand, with respect to its “brother” polymers such as PTFE and PFA, it has a lower melting temperature, about 40°C; It is a little more flexible than PTFE and its tensile strength is lower than PFA and PTFE. Normally, it is suggested to put FEP coating on the disc.
6) What is the burst pressure?
It is the numerical value expressed in units of PSIG or BARG (> to the operating pressure and < MAWP) given by the customer for the disc to break and relieve the protected equipment. This information should NEVER be assumed.
7) What is the rupture temperature?
It is the numerical value expressed in units of degrees Celsius (C°) or degrees Fahrenheit (F°) given by the customer for the disc to break. This should NEVER be assumed.
8) What is the operating pressure?
It is the numerical value where the process normally works in PSIG or BARG and that data is given by the client.
9) What is the operating temperature?
It is the numerical value where the process normally operates in degrees Celsius (°C) or degrees Fahrenheit (F°) and is data that is always provided by the client.
10) What is the maximum pressure MAWP (Maximum Allowable Woking Pressure) allowed in the vessel?
It is the maximum allowable gauge pressure at the top of a container at a specific temperature; is the ASME mandated base reference value for setting burst pressure limits. If a rupture disc exceeds the MAWP values, it may be the case that the container ruptures first before the disc.
It is important to consider that equipment loses properties over time, which is why the client must constantly evaluate the design pressure of the vessel.
The MAWP pressure should always be above the operating pressure and burst pressure. If the burst pressure is above the MAWP, disregarding ASME guidelines, the equipment would undoubtedly burst.
11) What kind of manufacturing range do you need of the rupture disc?
(Manufacturing Range) It is a type of tolerance that the customer must consider when selecting rupture discs and has to do with how accurately the disc is manufactured so that it ruptures at the rupture value.
It is expressed as 0, +0/-5%, +0/-10%, +-5%,+-10% and is the one stamped on the disc. Although it is always suggested to work with a manufacturing range equal to “zero”.
If two rupture values recorded on a rupture disk appear, it means that the Manufacturing Range is different from zero.
12) Does the rupture disk need to be fragmentable or non-fragmentable?
It is the possibility that a rupture disc, when opened, releases (fragmentable) metallic particles, unlike one that does not release material at the time of an explosion in the protected container. The cost of a fragmentable disk is less than a non-fragmentable one, although this type of disk is tending to disappear.
13) Where do you plan to place the rupture disc? (see graph)
Knowing where the rupture disc is going to be installed better guides its use and guarantees proper functioning of the disc. For example, the disc that works in series with a relief valve makes the latter’s seats last longer in the face of processes that are too chemically aggressive, preventing corrosion and the seat from sticking in the face of a viscous product. When working in parallel with a relief valve, it serves as a backup if the latter should fail. Whatever the case, the ASME gives burst pressure guidelines to protect the equipment.
14) What type of fluid does the process handle; liquid, vapor or gas?
If you work with a combination of two, you must keep in mind that there are rupture discs that only work for one thing and not the other.
15) Is there any suction (vacuum pressure) involved? (see graph)
Negative or vacuum pressure is that where the process crosses the “0 psig” barrier and causes the equipment to suffer a suction phenomenon at a given moment, causing the rupture disc to become fatigued. There are discs that work well in full vacuum (-1 barg), half vacuum (0.5 barg approx.) and others that cannot work in vacuum, hence the importance of knowing this phenomenon.
16) Is there pulse pressure involved (positive pressure variation)?
Pulses are those points such as maximums and minimums resulting from changes in the speed of a fluid, opening of valves or the incidence of injection of products with pumps. Rupture discs with a high presence of pulses can fatigue and rupture before the rupture pressure for which they were designed.
17) Is there back pressure involved? (see graph)
The inverted pressure is a counter pressure that is given to the rupture disc in the opposite direction of the flow, it influences the rupture value that the discs must have recorded; These always break due to the differential pressure between the flow and the counterflow.
Example:
If the rupture pressure (BP) of a disc is 100 psig and the backflow pressure is 0 psig, the rupture disc will rupture at a differential pressure of 100 psig (100 psig – 0 psig). But if the burst pressure (BP) of a disc is 100 psig and the backflow pressure is 10 psig, the disc will not rupture since it will be at a differential pressure of 90 psig (100 psig – 10psig); In this case the container must reach 110 psig for it to break (110 psig – 10 psig = 100psig). It is dangerous, if the design pressure of the vessel is at 105 psig, the vessel would break before the disc. For the rupture disc to rupture at 100 psig with a counterflow of 10 psig, the BP must be etched into the disc at 110 psig (110 psig – 10 psig = 100 psig).
18) Is there positive and negative pressure cycling involved? If there are, how many? (see graph)
It is when at a certain moment the process becomes cyclical in time going from positive to negative pressure, in this case, the value of how many cycles a process gives, it is only possible to be given with a graphic record, product of the signal that a pressure transmitter carries to a programmable logic controller (PLC) and that signal is recorded graphically in a Cartesian plane of pressure (P) versus time (t). The high cycling makes FIKE suggest the use with G2 technology, that is, a type of rupture disc that is made with a laser to prevent cycling fatigue from breaking them prematurely and outside the pressure for which it was designed.
19) How are you going to connect the RD to the process? (if you are not sure, answer: “at the provider’s discretion”)
The options can be: in “holder” disc holders, between flanges, clamp connection, threaded (see following graph). The connection of a disk must comply with international standards to be easily coupled to the process.
Example: If you have a FIKE type P rupture disc class 150# according to ASME B16.5 standard, the process connection must be the same since if it is of another standard or class it will not be able to connect to the equipment to be protected.
20) What is the type of material for the support (Holder / Disc holder)?
The holder is made up of two pieces called “inlet” or the one that has contact with the fluid and “outlet” that does NOT have contact with the process fluid but with the environment.
It is recommended that the “inlet” and “outlet” part must be made of the same material as the rupture disc. Other materials are available, including carbon steel (A/C) in order to reduce costs, but it must be clear what the contact fluid is and the working environment since chemical attack may occur on the holder.
21) Is any special certification needed for rupture discs?
Of the type FDA, ATEX, ASME, A3, ETC. Rupture discs are normally ordered with a standard rupture certificate, but requesting another type of certificate has an extra cost, even higher than the RD itself.
22) Do you need other accessories?
It turns out that FIKE handles additional accessories such as rupture indicators and vacuum supports. Breakage indicators are elements that operate based on a dry normally closed (NC) contact or filament that, when the disc breaks, interrupts an electrical signal carried by a cable to a controller, beacon or alarm, allowing a warning that there has been a rupture of the disc. Vacuum supports are those domes with perforations that are placed as an accessory to the rupture disc, preventing them from being damaged by implosion or excessive vacuum in the process.
Rupture discs should be selected only by those individuals with complete knowledge of the pressure relief requirements of the system to be protected, as well as the conditions surrounding the particular application.
Selection should NOT be based on arbitrary, assumed or incomplete conditions. The selection and sizing of the disks is the responsibility of the FIKE line specialist applications engineer as well as the user of the equipment to be protected. FIKE has representatives all over the world, such as in Colombia, where it has Flexilatina de Colombia, a company with extensive experience capable of helping you in the correct selection of your rupture disc. Leave the protection of your equipment in our hands.