How to set the on/off status for the safety valve backup and cut-off valve

Thread Content

【Question 1】Are the safety valves of the process units and pressure storage tanks in petrochemical enterprises in standby?    【Answer】It is recommended to determine this in accordance with standard specifications, process characteristics, and the actual maintenance cycle. [Reference 1] \"Selection and Installation of Safety Relief Devices for Pressure Equipment\" GB/T37816-2019, 5.1.4: In the following situations, it is necessary to consider installing two or more safety valves in parallel: a) To ensure the safe operation of pressure equipment, or when maintenance or replacement of the safety valves is required while the equipment continues to operate, two safety valves along with a rapid switching device for them should be installed, ensuring that each individual safety valve can meet the required safety relief capacity for the pressure equipment; b) When a single safety valve is not sufficient to meet the actual relief requirements of the pressure equipment, two or more safety valves should be installed; c) Under special operating conditions where there is a risk of failure of the safety valve itself, at least two safety valves should be installed. 【Reference 2】\"Code for Design of Process Piping in Refining Units\" (SH/T 3122-2013) 20.3 In any of the following situations, a backup safety valve should be installed in the relief system; the number of backup valves can be determined using the formula n+1 (where n is the number of safety valves required for normal operation): a) There is a history of leaks in the safety valves; b) The safety valves are clogged; c) The medium is corrosive; d) The medium tends to form scale; e) Online maintenance or inspection is required; f) There are other faults that affect the performance of the safety valves. [Reference 3] \"Code for Design of Tank Areas in Petrochemical Storage and Transportation Systems\" (SH/T 3007-2014), 6.4.2: The installation of safety valves on pressure storage tanks shall comply with the following provisions: d) Pressure storage tank safety valves shall be equipped with an online standby safety valve and one safety valve bypass line. One full-bore isolation valve should be installed before and after the safety valve, and \"LO\" (seal broken) should be indicated on the design drawings. For reference. 【Question 2】For the safety valves PSV (A/B) of the process units and pressure storage tanks in petrochemical enterprises, which are operated in one at a time with one as a backup, if isolation valves are installed at both the inlet and outlet, how should the switching states of these isolation valves be set? 【Answer】For the safety valves PSV (A/B) installed on the pressure vessels of the process units in petrochemical enterprises, one in service and one as backup, the inlet and outlet isolation valves of the safety valve PSV (A) are set to either sealed with lead (CSO) or locked open (LO) ； The inlet isolation valve of the backup safety valve PSV (B) is set to Sealed Closed (CSC) or Locked Closed (LC), while the outlet isolation valve is set to Sealed Open (CSO) or Locked Open (LO). In petrochemical plants, pressure storage tanks are equipped with one operating safety valve PSV (A) and one standby safety valve PSV (B). The standby safety valve PSV (B) should be set to online standby mode, while the inlet and outlet isolation valves for both the operating safety valve PSV (A) and the standby safety valve PSV (B) should be set to sealed open (CSO) or locked open (LO) mode.   [Reference 1] \"Code for Design of Process Piping in Refining Units\" (SH/T 3122-2013) 20.4 When there is a backup safety valve, isolation valves should be installed at the inlet and outlet of the safety valve. The inlet and outlet isolation valves of safety valves in normal operation should be sealed with lead or left unlocked; the inlet isolation valves of each safety valve should be sealed with lead or locked, while the outlet isolation valves should be sealed with lead or left unlocked. [Reference 2] \"Code for Design of Tank Areas in Petrochemical Storage and Transportation Systems\" (SH/T 3007-2014), 6.4.2: The installation of safety valves on pressure storage tanks shall comply with the following provisions: d) Pressure storage tank safety valves shall be equipped with an online standby safety valve and one safety valve bypass line. One full-bore isolation valve should be installed before and after the safety valve, and \"LO\" (seal broken) should be indicated on the design drawings.