What is the purpose of connecting a burst disc in series below the safety valve?

Generally, there is a concern that the medium will keep flowing out once the rupture disc fails; a safety valve can prevent this flow of medium, and it is an accessory to the rupture disc

Reply to 1# nbazxb: Installing a burst disc in front of the safety valve serves the following purposes: 1. If the medium is highly corrosive and requires special materials, it allows for the use of a less expensive material for the safety valve. 2. The medium is highly toxic, preventing the safety valve from achieving a complete seal. 3. Media containing particles (such as catalysts) may clog the safety valve.

I see, I thought it was to prevent the safety valve from activating

Reply to 3# yuzhilicn: I didn’t know about the interaction between safety valves and rupture discs before, but now I do! Thank you

Reply to 3# yuzhilicn: I fully agree with your explanation; these three reasons are all key aspects. Regarding the series connection of burst discs and safety valves, I would like to add some other reasons. Safety valves need to be calibrated at regular intervals to ensure they operate at the correct pressure. When a rupture disc is installed at the inlet of a safety valve, it is possible to remove the safety valve itself for calibration without having to shut down the system or disconnect the pipeline (according to standards, it is not allowed to install valves that can shut off flow in front of a safety valve or rupture disc, unless there are two safety valves connected in parallel and equipped with a switching valve) ； If installation is necessary, at least a seal should be applied to ensure it remains in the open position). The rupture disc is installed on the inlet side of the safety valve; a monitor must be placed between the rupture disc and the safety valve. This monitor consists of a tee fitting, to which a pressure gauge or pressure switch, as well as a relief valve, are connected. This setup is used to ensure that the gauge pressure in the cavity between the safety valve and the rupture disc remains zero, and the relief valve is used to discharge any positive or negative pressure that may leak into this cavity from behind the safety valve.