The rupture disc is connected in series with the backpressure setting of the safety valve
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The design pressure of the equipment is 6 MPa. The rupture disc is connected in series on the inlet side of the safety valve, with discharge to a tank at atmospheric pressure. In the initial design, the rupture pressure of the rupture disc and the setting pressure of the safety valve were both set at 6 MPa, with a back pressure of 0. Is there a problem?
It seems fine; the burst disc at the inlet should work just fine. If back pressure is considered at the outlet for the burst disc, it may not be able to function
Assuming that the rupture pressure of the burst disc and the setting pressure of the safety valve are both 6 MPa, with zero backpressure, and that the safety valve has not yet activated at the time the burst disc ruptures, will there be any danger due to the sharp increase in pressure in the pipeline between the safety valve and the burst disc?
There’s no danger; this pipeline will quickly reach 6 Mpa, after which the safety valve will activate. The regulations provide explanations for this usage, and there is plenty of information available online on this topic: https://wenku.baidu.com/view/fd53480552ea551810a6875d.html
Does back pressure refer to the pressure at which the system pressure remains stable behind the safety valve and rupture disc?
Remember that back pressure can be dynamic or static; it is necessary to take into account normal conditions as well as situations where there are other devices downstream that release pressure. Additionally, when a safety valve is connected in series downstream of a burst disc, an external small pipeline equipped with a pressure gauge and an EFV valve is usually installed between them. This pressure gauge should be able to indicate the current pressure as well as the peak pressures that have been reached; it can be manually reset to help determine whether the rupture disc has released pressure during inspections on site. Under normal conditions, the EFV valve keeps the cavity between the PSD and PSV in direct connection with the downstream area; however, it seals this connection when the PSD fails, ensuring that the PSV activates.
A pressure relief device needs to be installed between the burst disc and the safety valve
There are issues related to back pressure, which can be categorized into constant back pressure, cumulative back pressure, and superimposed back pressure. When discharging to a tank at atmospheric pressure, the constant back pressure is equal to 0; as for superimposed back pressure, it depends on whether there are other pressure relief pathways connected to the process system. Cumulative back pressure arises due to fluid flow, and it needs to be calculated based on the conditions of pressure release. In general, an estimate of the flow-induced back pressure can be made – for example, if the burst pressure is 6 MPa, the flow-induced back pressure could be estimated at 3%, or 0.18 MPa