Specification of Rupture Disk Burst Pressure
I say that the ASME only requires that the rupture disk pressure rating is less than MAWP at the temperature it is expected to rupture. DAMAGE RATIO – A damaged rupture disc will burst at some pressure other than FAS disc is ordered with a specific burst pressure at a specific temperature. A rupture disc is the pressure containing and pressure sensitive element of a rupture The specified disc temperature supplied to the rupture disc manufacturer.
Only if a single rupture disk is provided for more than one overpressure event; and if the relieving pressure for one of the events is at a coincident atmospheric temperature is the inpsectots observation correct. To prove your inspector wrong, you could requeset a Code Clarification. The more you learn, the less you are certain of. Although I agree that a vessel may never see an elevated pressure unless the temperature is also elevated, the potential still would exist from possibly an unknown or not thought of scenario.
That is why it must be protected even at ambient temperatures, from an over pressure event. Its still not required by the Code. Actually I don't have a big problem with what you state, since so many of our engineers miss the boat when they size a relief system; and because a stamped burst pressure greater than MAWP does confuse operating personnel - who we often ask to audit the process. But we need to stay clear on what is plant preference and what is stated in the Code.
But after a plant is built and ages; trying to up capacity can get you into this type of problem.
Focus on Rupture Discs and Pressure Relief - Chemical Engineering
Then the inspector and the plant need to be able to communicate and work together; there is no excuse for undefined overpressure scenarios. Remember there are two kinds of tolerances built into the design of a rupture disk: The manufacturer may stamp the disk anywhere in this range unless you request a tighter mfg.
So if the disk is stamped for example at psig between and then the code guarantees actual disk rupture between In your example, if you used a tension type disk, the maximum operating pressure must be limited to 0. Disk burst pressure is not determined like relief valve set points are many people make this mistake.
Apologize if you alrady knew all this; but it may help others. Apologize if you already knew all this; but it may help others. The other issue, surrounding the pressure rating at ambient temperature, the code does not allow an exception just because you are operating at higher temperatures.
Otherwise one might experience an overpressure event, exceeding the MAWP, due to fire exposure to the bottom of the vessel, where the rupture disc, located above, is at ambient temperatures.
I have referenced the code and interpretations already and found no exceptions. If it is needed to have a rupture disc that is that close to the MAWP, I would suggest that they use a composite material disc which is less temperature dependant and has a tighter tolerance. If the disk is at top of tank and fire is beneath tank, the designer should have the disk rated to burst at the actual disk temperature ambient in your example.
Why is this so? The temperature most commonly specified is that of the relieving fluid coincident with the burst pressure, i.
Focus on Rupture Discs and Pressure Relief
Sounds logical, but remember that the disk is continuously exposed to the process stream for hours, days, weeks or even months before it may ever be needed. Or, the disk may be exposed to ambient conditions. Therefore, expect the disk temperature to be approximately equal to its environment during normal operation of the system. When a process upset occurs, system pressure rises until it reaches relief burst.
The temperature of the relieving fluid also rises per thermodynamics. However, the time interval between normal system operation and relief is usually so small that the rupture disk's temperature hardly has time to come to equilibrium with the higher process fluid temperature. Therefore the disk can actually be colder than it's specified temperature. In general, burst pressure varies inversely with temperature.Rupture Disk or Pressure safety disc
For some rupture disks, the burst pressure can be as much as 15 psi greater than stamped if the actual temperature is oF lower than specified, e. This doesn't sound like a big difference but if psig were the design pressure or MAWP of the vessel, then a burst pressure of psig would be in violation of code LAW.
The opposite is also true. A disk at a temperature hotter than specified when called into service will burst at a pressure lower than stamped.