In industrial production, safety valves are crucial devices that ensure the safety of equipment and personnel. They act like silent guardians, promptly opening to release excess pressure when the pressure of the equipment exceeds the safe range, thus preventing accidents. However, the installation of safety valves is a complex and delicate task, with every step being of vital importance. This article will provide a detailed introduction to the key points of safety valve installation, aiming to help relevant staff better understand and master this knowledge to ensure the safe and stable operation of industrial production.
Safety valves should be installed as close as possible to the equipment or piping they are designed to protect. This reduces the delay in pressure transmission, allowing the safety valve to respond more quickly to abnormal conditions. Additionally, the installation location should be accessible for maintenance and adjustment, with sufficient space around it to facilitate routine maintenance and emergency handling.
For safety valves on pressure vessels, they should be installed in the vapor space above the liquid level of the vessel, or on piping connected to the vapor space of the pressure vessel. This ensures that the safety valve is not submerged in liquid during normal operation, which could affect its proper opening.
When dealing with containers or equipment holding flammable, toxic, or viscous media, special attention must be paid to the installation of safety valves. A shut-off valve can be installed in front of the safety valve, but its flow area must not be smaller than the minimum flow area of the safety valve. Moreover, it should be lead-sealed to ensure that the shut-off valve remains fully open and in a constant open state. This prevents the shut-off valve from being accidentally closed, which could interfere with the normal operation of the safety valve. The safety valve should also be installed in the opposite direction to the shut-off valve to minimize the impact of the valve's own weight, avoiding stress fatigue and discharge vibration fatigue.
For safety valves that may be blocked or corroded by materials, a rupture disc should be installed before the inlet of the safety valve, and a check valve should be added between the safety valve and the rupture disc. Additionally, measures such as back-blowing, steam tracing, or insulation should be taken on the inlet piping to ensure the unobstructed flow into the safety valve.
Safety valves installed on piping should be located in areas where the fluid pressure is relatively stable and at a certain distance from sources of pressure fluctuations. They should not be installed in dead ends of horizontal piping. For piping, heat exchangers, or pressure vessels containing liquid media, when valve closure may cause thermal expansion and result in increased pressure, the safety valve can be installed horizontally to directly discharge the liquid downward. This utilizes the force of gravity to facilitate the smooth discharge of the liquid, reducing the risk of pressure accumulation.
The design of the safety valve's discharge piping is equally important. When discharging to the atmosphere in an emergency, the pipe outlet should be smooth, non-sharp, and free of burrs to prevent static electricity discharge. The installation point of the safety valve should not subject the valve to excessive back pressure, which should be within the specified allowable range. The valve body of the safety valve should be securely supported to ensure that it does not shift or vibrate due to external forces during operation.
For containers holding extremely or highly hazardous media, or flammable and explosive media, the discharge outlet of the safety valve should be directed to a safe location and properly treated. When two or more safety valves share a single discharge pipe, the cross-sectional area of the discharge pipe should not be less than the sum of the cross-sectional areas of all the safety valve outlets. However, it should be noted that oxygen or flammable gases, as well as any two gases that can chemically react with each other, should not share a discharge pipe to avoid dangerous chemical reactions.
For corrosive media, safety valves should be installed in combination with rupture discs to enhance protection. For highly toxic media, safety valves with good sealing properties should be selected to prevent the leakage of harmful media. For safety valves handling high-temperature media, since high temperatures can significantly affect springs, spring-loaded safety valves should be avoided to ensure accurate operation.
For important safety valves or those that are susceptible to fire damage, a spray protection system should be installed to prevent fire from damaging the safety valve and affecting its normal operation. For safety valves used on spherical tanks, dual safety valves should be installed, with each safety valve having a discharge capacity that meets the safety relief requirements of the spherical tank to ensure its safety in emergency situations.
Safety valves should be equipped with static electricity bonding to prevent safety hazards caused by static electricity accumulation. To prevent the safety valve from repeated opening and closing, which can cause vibration and damage the valve, the pressure drop in the inlet piping of the safety valve should be reduced, i.e., by increasing the inlet pipe diameter and shortening the inlet pipe section. Safety valves should be installed vertically and located in the vapor space above the liquid level of the pressure vessel or on piping connected to the vapor space of the pressure vessel.
The connecting pipes and fittings between the pressure vessel and the safety valve should have a cross-sectional area that is not less than the inlet cross-sectional area of the safety valve, and the connection pipe should be as short and straight as possible. When two or more safety valves are installed on a single connection port of a pressure vessel, the inlet area of that connection port should be at least equal to the sum of the inlet cross-sectional areas of these safety valves.
Generally, shut-off valves should not be installed between the safety valve and the pressure vessel. However, to enable online testing of the safety valve, a rupture disc device can be installed between the safety valve and the pressure vessel. For pressure vessels containing extremely, highly, or moderately hazardous media, flammable media, corrosive or viscous media, or valuable media, to facilitate the cleaning and replacement of the safety valve, with the approval of the technical person in charge of pressure vessel safety of the user unit and the formulation of reliable preventive measures, shut-off valves can be installed between the safety valve (rupture disc device) and the pressure vessel.
During normal operation, the shut-off valve must be fully open (lead-sealed or locked), and its structure and bore size should not hinder the safe discharge of the safety valve. The installation location of the safety valve should be convenient for inspection and maintenance to ensure that staff can promptly detect and address potential issues.
New safety valves should come with a product qualification certificate. Before installation, they should be retested, lead-sealed, and accompanied by a safety valve calibration report. Safety valves should be installed vertically and located at the vapor interface position of the container or piping. The outlet of the safety valve should be free of resistance to avoid back pressure. If a discharge pipe is installed, its inner diameter should be larger than the outlet bore of the safety valve. The discharge outlet of the safety valve should be protected against freezing. For containers holding flammable or toxic, highly toxic media, the discharge pipe should lead directly to a safe location outdoors or to a facility for proper treatment, and no valves should be installed on the discharge pipe.
No valves should be installed between the pressure-bearing equipment and the safety valve. For containers holding flammable, explosive, toxic, or viscous media, a shut-off valve can be installed to facilitate replacement and cleaning, but its structure and bore size should not interfere with the normal operation of the safety valve. During normal operation, the shut-off valve must be fully open and lead-sealed. For pressure vessels containing flammable, explosive, or toxic media, the discharged media from the safety valve must have safety devices and a recovery system.
The installation of lever safety valves must maintain a vertical position, and spring safety valves are also best installed vertically to avoid affecting their operation. During installation, attention should be paid to the coordination and coaxiality of the parts, and all bolts should be evenly tightened. The cross-sectional area of the connecting short pipe between the safety valve and the boiler pressure vessel should not be less than the flow cross-sectional area of the safety valve. The entire safety valve should be installed on a single connection pipe, and the cross-sectional area of the connection pipe should be at least 1.25 times the total flow cross-sectional area of the safety valve.
When the container contains both gas and liquid phases, the safety valve should be installed in the gas phase. When the safety valve is used to discharge flammable liquids, the outlet of the safety valve should be connected to an accident storage tank. When the discharged material is a high-temperature flammable substance, the receiving container should have corresponding protective facilities. Generally, safety valves can be vented on-site, with the vent outlet being more than 1 meter (m) above the operator and not directed towards open flames, spark-emitting locations, or high-temperature equipment within 15 meters (m). The vent outlet of safety valves for indoor equipment or containers should be led out of the roof and more than 2 meters (m) above the roof.
When there is an isolation valve at the inlet of the safety valve, the isolation valve should be kept in a constant open state and lead-sealed to prevent mistakes. The cross-sectional area of the connecting pipes and fittings between the safety valve and the boiler or pressure vessel should not be less than the inlet cross-sectional area of the safety valve. If several safety valves share a single inlet pipe, the flow cross-sectional area of the inlet pipe should not be less than the sum of the inlet cross-sectional areas of the safety valves.
Generally, shut-off valves or steam extraction pipes should not be installed between the safety valve and the boiler's steam drum or header. Similarly, it is not advisable to install shut-off valves or other extraction pipes between the safety valve and the pressure vessel. For pressure vessels containing extremely, highly, or moderately hazardous media, flammable, corrosive, viscous media, or valuable media, with the approval of the technical person in charge of pressure vessel safety of the user unit and the formulation of reliable preventive measures, shut-off valves can be installed between the safety valve and the pressure vessel. During normal operation of the pressure vessel, the shut-off valve must remain fully open, lead-sealed or locked. The structure and bore size of the shut-off valve should not hinder the safe discharge of the safety valve.
Spring-loaded safety valves with threaded connections should be connected to a short pipe with threads, and the short pipe should be welded to the shell or header. A discharge pipe must be installed for the safety valve. The discharge pipe should avoid bends and sharp turns as much as possible to minimize resistance. The discharge pipe should lead directly to a safe location and have sufficient cross-sectional area to ensure smooth steam discharge.
For safety valves that can chemically react with each other, they should not share a single discharge pipe. When safety valves are installed on equipment containing corrosive or flammable gases, measures should be taken to prevent corrosion or fire and explosion during discharge. When the equipment with a safety valve contains toxic media, and the vapor density of the media is greater than that of air, the discharged media and vapors should be directed into a closed system and recovered from the closed system for use in production.
For safety valves installed outdoors, reliable measures must be in place to prevent the freezing of moisture in the valve's media when the temperature falls below 0℃, which could affect the discharge of the safety valve. If the crystallization temperature of the safety valve's media is higher than the lowest ambient temperature, the safety valve must be equipped with an insulation jacket and an insulation steam blow-off device to prevent media crystallization from blocking the safety valve and affecting its normal operating performance. The inlet and outlet pipes of the safety valve must also be designed with steam-insulated jacket pipes or additional insulation steam tracing pipes to prevent media crystallization from blocking the pipes.
Safety valves should have devices to prevent the weight from moving on its own and guide frames to limit the lever from derailing. Spring-loaded safety valves should have lifting handles and devices to prevent the casual adjustment of the adjustment screws. They should be installed vertically at the highest position of the drum or header. No steam extraction outlet pipes or valves should be installed between the safety valve and the drum or header.
For boilers with a rated steam pressure less than or equal to 3.82 MPa, the throat diameter of the safety valve should not be less than 25 mm; for boilers with a rated steam pressure greater than 3.82 MPa, the throat diameter of the safety valve should not be less than 20 mm. It is best to install the safety valve directly at the highest position on the pressure vessel itself. The safety valve for liquefied gas storage tanks must be installed in the vapor section. Generally, a short pipe can be used to connect to the container, and the diameter of this short pipe should not be less than the valve diameter of the safety valve.
Boilers with a rated evaporation capacity greater than 0.5 t/h should have at least two safety valves installed; boilers with a rated evaporation capacity less than or equal to 0.5 t/h should have at least one safety valve. Safety valves must be installed at the outlet of the separate economizer and the outlet of the steam superheater. The outlet of the safety valve should be free of resistance to avoid back pressure. If a discharge pipe is installed, its inner diameter should be larger than the outlet bore of the safety valve. The discharge outlet of the safety valve should be protected against freezing. For containers holding flammable or toxic, highly toxic media, the discharge pipe should lead directly to a safe location outdoors or to a facility for proper treatment, and no valves should be installed on the discharge pipe.
Although the installation of safety valves may seem cumbersome, it is of great significance. It directly affects the safe and stable operation of industrial production and the safety of equipment and personnel's lives and property. Through scientific and rational installation, safety valves can maintain good working conditions, effectively release pressure from equipment or piping in a timely manner, and ensure the smooth progress of industrial production. Additionally, this can extend the service life of safety valves, reduce equipment maintenance costs, and improve the economic benefits of enterprises.
In summary, the installation of safety valves is a systematic task that requires staff to have solid professional knowledge and a rigorous work attitude. Only by strictly following relevant standards and specifications can safety valves play their due role in industrial production and safeguard the safe production of enterprises.