Selection of 1. safety valve

The general principle of safety valve selection is to determine the nominal pressure of the safety valve by the operating pressure, the operating temperature of the safety valve is determined by the operating temperature range, the constant pressure value of the safety valve is calculated by the constant pressure range of the spring or lever, and then the material and structure type of the safety valve are determined according to the working quality, and the diameter of the flow passage of the safety valve is calculated according to the safety discharge volume.

1Structure type

Safety technical specifications have corresponding provisions according to its provisions, such as steam boiler safety valve should be full open spring safety valve, lever safety valve and control safety valve

2Nominal pressure

The operating temperature determines the operating temperature range of the safety valve(When the temperature is higher than the material reference temperature, pay attention to the principle of "temperature rise and pressure drop").

32. Spring pressure level

The spring pressure level range marked by the safety valve matches the setting pressure required for the safe operation of the protected equipment. During the inspection, the inspectors must carefully check according to the required parameters and technical data.

4Nominal diameter

The discharge capacity of the safety valve should be greater than or equal to the safety discharge of the protected equipment, the flow diameter of the safety valve should be calculated according to the relevant standards, and then according to the calculation of the flow diameter combined with the safety valve type selection to meet the requirements.

5Materials

The main parts of the safety valve, such as the valve body, can be made of different materials according to different media. For occasions with low temperature and pressure, such as air storage tanks, cast iron can be used. General temperature and pressure can be made of high-quality carbon steel. High-temperature media can be made of chromium molybdenum or chromium molybdenum vanadium alloy steel, and corrosive media can be made of acid-resistant stainless steel.

2. verification

1Calibration cycle

（11) Safety valves in use are generally calibrated at least once a year. For the spring-loaded safety valve, when the conditions specified in Article 17 of the Rules for Periodic Inspection of Pressure Vessels are met, the calibration cycle can be appropriately extended with the approval of the technical director of the user unit.

（24) The newly installed safety valve of the equipment shall be calibrated according to the operating conditions before putting into use, and the safety valve with disassembled, repaired or replaced parts shall be calibrated again.

2Setting pressure

The function of the safety valve is used to protect the safety of the equipment. Unless the equipment is used for depressurization due to strength problems, the setting pressure value of the safety valve should generally be calculated on the basis of the rated working pressure of the boiler and the design pressure of the pressure vessel, instead of the use pressure required by the production process. Otherwise, the safety valve will move unnecessarily frequently, which is not conducive to stable production and material waste, even lead to environmental pollution. Therefore, the setting pressure of the safety valve is not adjusted as low as possible under the premise of ensuring the safety of the protected equipment. Because the load of the equipment will change during operation, when the working condition and gas consumption change, the pressure will also fluctuate.  　　

3Verification method

On-line checksum and check station. Boiler safety valve in the conditions permit should be as far as possible in the field calibration (online calibration), because the field calibration is more in line with the actual operating conditions, and therefore more reliable. For the safety valve used for toxic, explosive and corrosive media, taking into account the inability to achieve recovery and inspection of the media after the valve back seat and leakage and other issues, generally do not advocate online calibration. The calibration medium on the calibration table is generally air or nitrogen.

3. installation

（13) The safety valve on the equipment shall be installed vertically.

（22) Generally, it is installed close to the protected equipment. The installation position is easy to maintain and check, and the connecting pipe is as short and straight as possible.  　　

（34) Boiler steam safety valve is installed at the highest position of boiler drum and header, or at the highest position of gas phase space above the liquid level of protected equipment; liquid safety valve is installed below the normal liquid level.

（4) The diameter of the inlet pipe of the safety valve shall not be less than that of the safety valve. If several safety valves share an inlet pipe, the cross-sectional area of the inlet pipe shall not be less than the sum of the inlet cross-sectional areas of these safety valves.

（5) It is generally not suitable to install a stop valve between the safety valve and the equipment. For the equipment containing toxic, explosive, corrosive, viscous medium or valuable medium, the stop valve installed between the safety valve and the equipment must ensure that the stop valve is fully open during the normal operation of the equipment, and the structure and diameter of the stop valve shall not hinder the safe discharge of the safety valve, and the discharge outlet of the safety valve shall be equipped with a conduit to lead the discharge medium to a safe place, safety valve outlet pipe diameter is not less than the outlet diameter of the safety valve.

4. Routine Maintenance

（11) Check regularly. In order to prevent the valve disc and valve seat of the safety valve from sticking, the manual discharge test should be done regularly on the safety valve.

（24) Routine maintenance and inspection of safety valve.

To sum up, the safety valve as the equipment overpressure protection of the last line of defense, should effectively strengthen the management, to ensure that the safety valve in the action process to do sensitive open, sufficient discharge, timely back to the seat, reliable sealing, so as to prevent the equipment due to overpressure caused by safety accidents.