Rupture Disc

[Vishal Kumar]

Dear. Everyone , i am graduate engineer ...i have enormous doubts so please provide me the correct path...
Q,1) Rupture disc Burst pressure/Set pressure is between Operating pressure and vessel MAWP ?
Q,2) I need guidance for RD Sizing as i have to carry it out during P&id prep.

 

[The Obturator]

Hi. Basically;-
Q1). Burst Pressure of Rupture Disc should equal Set Pressure of Pressure Relief Valve (if the rupture disc is upstream/PRV Inlet).
Q2.) There are many other issues to familiarise yourself with on Bursting Disc selection and sizing. I suggest your read the Rupture Disc Section in API-520 (2014) and also the corresponding specification in ASME VIII (2019) Section UG-134. These 2 specs will answer your doubts.

Per ISO-4126, only the term Safety Valve is used regardless of application or design.

 

[Vishal Kumar]

Thanks a lot will come back with doubts if in case one arrives.

 

[georgeverghese]

General practice is max normal operating pressure should be no more than 80% of RD setpoint pressure. RD set pressure is generally set no higher than vessel MAWP. See RD vendor sizing guidelines in their catalogues for sizing procedures. There is a general preference for reverse buckling type RD. Beware that RD actual bursting pressure is strongly influenced by vent / flare system backpressure, since these are basically dp devices. Wherever possible, avoid using these.

 

[The Obturator]

I'll add that there are differences in application whether the Rupture Disc is to be used upstream of a PRV (inlet) or on it's own as a single Non-Reclosing Pressure Relief Device. Very important to know the operating to burst pressure ratio as different manufacturers have different offerings and limitations. As georgeverghese states, operating pressure should generally be no more than 80%. Some manufacturers claim their designs can have operating pressures up to 95%, but these applications will be limited. Another publication to familiarise is ISO-4126-2.

Per ISO-4126, only the term Safety Valve is used regardless of application or design.

 

[LittleInch]

Also you really need to understand why a RD is being used in the first place instead of a relief valve.

It is usually either because there is a need for a high flow very sudden rise in pressure, typically on the shell side of a high pressure tube HX or the fluid is toxic or corrosive so you really don't want it to leak past a relief valve.

There are downsides and one as noted is that you really need a decent gap between MOP and set pressure of the disc and also you really don't want a high pressure in the vent system as there is no real way to isolate the downstream pressure influence and RD's don't like negative pressure or highly variable pressure (fatigue issues).

Sizing?
Basically RD's end up as a full bore opening very very quickly. Sizing is therefore all about vent capacity and back pressure.

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