What are the requirements for the setting and selection of safety valves?

Time：2022/1/27 21:06:53 Category：TECHNICAL ARTICLE Source： Click：

1、 Setting of safety valve

A safety valve must be installed in one of the following 11 cases:

1. Independent pressure system (with shut-off valve separated from other systems). The system refers to all gas phase, all liquid phase or connected with gas phase.

2. Overpressure caused by abnormal reactor.

3. Where there is no safety valve at the pressure material source of the container.

4. Vessels and pipes whose design pressure is less than the pressure at the pressure source.

5. Outlet piping for positive displacement pumps and compressors.

6. A container that produces overpressure due to the accumulation of non condensable gas.

7. If a shut-off valve or control valve is set on the outlet pipeline of the heating furnace, a safety valve shall be set upstream of the valve.

8. Overpressure parts caused by process accidents, automatic control accidents, power accidents, fire accidents and utility accidents.

9. The part where the liquid expands due to the closing of valves at both ends.

10. Steam outlet pipe of condensate turbine.

11. In some cases, due to the leakage of the check valve at the outlet of the pump, a safety valve is set on the inlet pipe of the pump.

2、 Typical setting mode of safety valve

1. Mode 1: only one safety valve is installed, and there is no block valve at the front and back of the safety valve.

2. Mode 2: only one safety valve is installed, and block valves are added at the front and back of the safety valve.

3. Mode 3: only one safety valve is installed, and block valve and auxiliary line valve are added at the front and back of the safety valve.

4. Mode 4: only one safety valve is installed, and a group of bursting discs are installed in front of the safety valve; A four-way component interface for on-line calibration is installed between the bursting disc and the safety valve.

5. Mode 5: only one safety valve shall be installed, and a group of bursting discs shall be installed in front of the safety valve; A four-way component interface for on-line calibration is installed between the bursting disc and the safety valve, and a block valve is installed in front of the bursting disc and behind the safety valve.

6. Mode 6: install two safety valves at the same time, and install a block valve at the front and rear of each safety valve, so that the safety valves can be standby for each other.

3、 Selection of typical methods

1. If one of the following conditions is met, the safety valve shall be set according to mode 1:

(1) In the operation unit of intermittent or batch production, it can meet the requirements of one school a year;

(2) In order to meet the requirements of annual calibration of safety valve, when the materials in the equipment can be emptied.

2. For equipment that needs to operate continuously for more than one year, and within the time of safety valve calibration, other measures can be taken to ensure that the system does not overpressure, and the safety valve shall be set according to mode 2.

3. If one of the following conditions is met, the safety valve shall be set according to mode 3:

(1) During the calibration time of safety valve, other measures cannot be taken to ensure that the system does not overpressure;

(2) When starting and stopping, it is necessary to discharge materials through the auxiliary line valve of the safety valve.

4. If one of the following conditions is met, the safety valve shall be set according to mode 4:

(1) When the medium is viscous medium, corrosive medium, self aggregation of medium and solid particles in the medium;

(2) When a safety valve is installed and only bursting discs can meet the requirements of on-line calibration.

5. Under the condition of Article 4 of this article, and when the bursting disc needs to be replaced online within the operation cycle of the equipment, the safety valve shall be set according to mode 5.

6. When the above methods cannot meet the requirements of "generally, it shall be calibrated at least once a year", set parallel standby safety valves according to mode 6, and seal them with lead to make them in the state of one opening and one closing.

7. According to the needs of the system, when a relief source is equipped with two or more safety valves, in order to meet the requirements of "generally, it should be calibrated at least once a year", one of the above six methods should be selected to meet the use requirements and be equipped in an economical way.

8. Safety valves with special requirements for process shall be set according to relevant regulations.

4、 Selection of safety valve

1. For the expansion and pressure relief of incompressible liquid, it is advisable to select micro open safety valve or full open safety valve. When the medium is liquid and the full open safety valve is selected, its action performance becomes micro open type, and the inner diameter of its nozzle shall be calculated according to the micro open type.

2. Spring type safety valve or pilot type safety valve shall be selected under general process conditions.

3. Balanced Bellows Safety valve shall be selected under the following conditions:

(1) When the back pressure of the safety valve is greater than 10% of its set pressure but less than 30%;

(2) When the medium is corrosive, easy to scale and coke, which will affect the normal operation of the safety valve spring;

However, the Balanced Bellows Safety valve is not suitable for the media such as phenol, wax liquid, heavy stone oil fraction and coke powder, nor for the selection of reciprocating compressor.

4. Pilot operated safety valve shall be selected under the following conditions:

(1) When the back pressure of the safety valve is more than 30% of its set pressure;

(2) Occasions requiring particularly good sealing performance of safety valve;

(3) When the medium is toxic and harmful, the non flowing pilot valve shall be selected (that is, when the pilot valve is opened, it does not discharge the medium).

5. Except for the safety valves for water, steam, air and nitrogen, all safety valves shall be of closed spring structure.