3.6 Stems and packing
The threaded part of the valve stem should not be in contact with the conveying fluid, except for the special requirement, and the valve stem and stem nut assembly should be self-locking. The valve stem and packing should be resistant to various corrosion. The packing should meet the requirements of Q/BU.J1502-93. The packing shall be ring shaped packing made of graphite and expanded graphite.
3.7 Hard alloy surfacing
Try to avoid surfacing cobalt-based cemented carbide on stainless steel containing 12% to 17% Cr. Nuclear specification valves should comply with the requirements of S8000 "Abrasion-resistant surfacing on carbon steel, low-alloy steel or alloy steel" in the "Rules for the Design and Construction of Nuclear Island Machinery and Equipment".
3.8 Driving devices
When the handwheel rotates in a clockwise direction, the valve is closed, and the direction and the words "open" and "close" should be marked on the handwheel.
(1) Manual devices
The design of the manual gate valve should allow the replacement of an electric drive mechanism. For operating devices that rotate 90°, the length of the handle is related to the valve size. In the open position, the handle is in the same direction as the flow of the medium. In order to reduce errors, the handle should be equipped with a device to prevent misoperation to ensure that the handle is only fixed in the same position.
(2) Electric devices
In working conditions where both manual and electric operations are available, electric devices should be used first. The handwheel should be automatically removed from the drive mechanism. The stem nut should not be integrated with the electric drive mechanism. The electric drive mechanism should be disassembled without removing the nut from the valve stem. For the backup manual operating device, when it is equipped with a gear reduction device with a reduction ratio greater than 10, it should also be equipped with a visual indicator of the torque switch action. The electric actuator should also meet the EJ/T1022.11 specification. The connection between the valve and the actuator should be self-locking, and the motor must be waterproof and dustproof (protection grade IP55); the insulation performance should be compatible with the operating conditions. The operating mode of the torque switch should allow the drive with two directions. The torque switch should be the dynamometer type, and can be tripped when overloaded. Continuous and reliable sealing force of discs must be ensured for globe valves and diaphragm valves.
In the normal closing process of parallel gate valves and ball valves, the electric actuator is stopped by the limit switch when the disc reaches the specified position. The torque switch is only used when the limit switch fails or an operation accident occurs. A full opening is operated by a limit switch. The torque switch serves as a backup. In the normal closing process of wedge gate valves, parallel gate valves with double plates and globe valves, the electric actuator drives the disc and it is stopped by the torque switch; the limit switch can act as a position detector. The full opening is operated by the limit switch, and the torque switch is used as a backup.
(3) Pneumatic devices
Pneumatic valves should be equipped with manual operation devices as a backup (except for special regulations). The design should ensure that the medium does not leak to the outside world in the disassembly process of the operating device. Unless there is a special requirement, all pneumatic valves should be equipped with a spare manual operating mechanism, and there should be open and closed position indications, intermediate position indications (if required), lockable in the middle position (if required) and easy to disassemble.
For regulating valves, the manufacturer should prepare the size report of the actuator and all parameters in it must be verified and approved. The upper housing of the actuator should be detachable. For the pressure of the instrument compressed air distribution system (SAR), please refer to the procurement requirements and list of the valve. The actuator should be able to perform its functions within the air source pressure range under the operating conditions specified in the valve list. When the valve is under pressure, the actuator should be able to be disassembled. Generally, except for the regulating valve with a packing compression device, the actuator should be designed as a detachable type without affecting the sealing performance of the valve stem.
The actuator should have the characteristics of storing energy, so that the valve can return to the safe position (the open or closed position) in the case of loss of air supply or power supply. The safe position is determined by the procurement requirements and list of the valve. This system should keep the valve in a safe position under the maximum pressure difference and special environmental conditions.
3.9 Position indicators
All valves shall be provided with clear indication marks for opening and closing positions. All electric valves shall be equipped with a visual indicator for the position of the disc. For parallel gate valves, the valve seat should be in the closed position. The valve stem's limit switch shall have electrical contacts for indication and control functions. The requirements of the electric valve's limit switch shall comply with the requirements of Electric Devices for Valves of PWR Nuclear Power Plants.
3.10 The leakage extraction of the packing
To ensure the sealing of the valve stem of the nuclear standard valve, the structure of the double-packing intermediate leakage extraction ring and leakage extraction pipe should be adopted, except for special regulations. The leakage extraction tube should be a straight tube with 10 meters and 21.3mm x 2.77mm.
3.11 Other devices
Except for electric valves, all isolation valves should be equipped with locking devices so that the valves can be locked in the open or closed position. The wedge gate valve should be designed to prevent the valve stem from rotating in the valve body to avoid damage to the sealing surface. The bolts within the pressure-bearing boundary shall be designed with mechanical locking devices.
3.12 Materials for valve parts
If the valve body is made from stainless steel, stainless steel should also be adopted for the remaining parts in contact with the conveying medium.
3.13 Interchangeability
All the same parts of the same type of valve should be interchangeable with each other.
3.14 Transportation
Valves weighing more than 30 kg should have lifting lugs, or indicate the lifting position during transportation in the figure.
4. Conclusion
According to the actual operating conditions of nuclear power valves, the technical characteristics and requirements of nuclear power valves are stricter than those of thermal power and hydropower valves. In addition to the technical requirements of conventional valves, finite element analysis and seismic calculation analysis are also required, the limit calculation of the primary film stress, the limit calculation of the primary film stress plus bending stress, and the circuit start-stop cycle-related calculation of the limit calculation of the amplitude of the primary and secondary stress changes and the design of the stuffing box's anti-leakage structure are also required. Pollution of impurities in the medium, ambient temperature, operating temperature, ambient humidity, radioactive DC power supply and voltage fluctuations, and stable technical requirements under related earthquake and vibration conditions and safety levels should also be considered.
The threaded part of the valve stem should not be in contact with the conveying fluid, except for the special requirement, and the valve stem and stem nut assembly should be self-locking. The valve stem and packing should be resistant to various corrosion. The packing should meet the requirements of Q/BU.J1502-93. The packing shall be ring shaped packing made of graphite and expanded graphite.
3.7 Hard alloy surfacing
Try to avoid surfacing cobalt-based cemented carbide on stainless steel containing 12% to 17% Cr. Nuclear specification valves should comply with the requirements of S8000 "Abrasion-resistant surfacing on carbon steel, low-alloy steel or alloy steel" in the "Rules for the Design and Construction of Nuclear Island Machinery and Equipment".
3.8 Driving devices
When the handwheel rotates in a clockwise direction, the valve is closed, and the direction and the words "open" and "close" should be marked on the handwheel.
(1) Manual devices
The design of the manual gate valve should allow the replacement of an electric drive mechanism. For operating devices that rotate 90°, the length of the handle is related to the valve size. In the open position, the handle is in the same direction as the flow of the medium. In order to reduce errors, the handle should be equipped with a device to prevent misoperation to ensure that the handle is only fixed in the same position.
(2) Electric devices
In working conditions where both manual and electric operations are available, electric devices should be used first. The handwheel should be automatically removed from the drive mechanism. The stem nut should not be integrated with the electric drive mechanism. The electric drive mechanism should be disassembled without removing the nut from the valve stem. For the backup manual operating device, when it is equipped with a gear reduction device with a reduction ratio greater than 10, it should also be equipped with a visual indicator of the torque switch action. The electric actuator should also meet the EJ/T1022.11 specification. The connection between the valve and the actuator should be self-locking, and the motor must be waterproof and dustproof (protection grade IP55); the insulation performance should be compatible with the operating conditions. The operating mode of the torque switch should allow the drive with two directions. The torque switch should be the dynamometer type, and can be tripped when overloaded. Continuous and reliable sealing force of discs must be ensured for globe valves and diaphragm valves.
In the normal closing process of parallel gate valves and ball valves, the electric actuator is stopped by the limit switch when the disc reaches the specified position. The torque switch is only used when the limit switch fails or an operation accident occurs. A full opening is operated by a limit switch. The torque switch serves as a backup. In the normal closing process of wedge gate valves, parallel gate valves with double plates and globe valves, the electric actuator drives the disc and it is stopped by the torque switch; the limit switch can act as a position detector. The full opening is operated by the limit switch, and the torque switch is used as a backup.
(3) Pneumatic devices
Pneumatic valves should be equipped with manual operation devices as a backup (except for special regulations). The design should ensure that the medium does not leak to the outside world in the disassembly process of the operating device. Unless there is a special requirement, all pneumatic valves should be equipped with a spare manual operating mechanism, and there should be open and closed position indications, intermediate position indications (if required), lockable in the middle position (if required) and easy to disassemble.
For regulating valves, the manufacturer should prepare the size report of the actuator and all parameters in it must be verified and approved. The upper housing of the actuator should be detachable. For the pressure of the instrument compressed air distribution system (SAR), please refer to the procurement requirements and list of the valve. The actuator should be able to perform its functions within the air source pressure range under the operating conditions specified in the valve list. When the valve is under pressure, the actuator should be able to be disassembled. Generally, except for the regulating valve with a packing compression device, the actuator should be designed as a detachable type without affecting the sealing performance of the valve stem.
The actuator should have the characteristics of storing energy, so that the valve can return to the safe position (the open or closed position) in the case of loss of air supply or power supply. The safe position is determined by the procurement requirements and list of the valve. This system should keep the valve in a safe position under the maximum pressure difference and special environmental conditions.
3.9 Position indicators
All valves shall be provided with clear indication marks for opening and closing positions. All electric valves shall be equipped with a visual indicator for the position of the disc. For parallel gate valves, the valve seat should be in the closed position. The valve stem's limit switch shall have electrical contacts for indication and control functions. The requirements of the electric valve's limit switch shall comply with the requirements of Electric Devices for Valves of PWR Nuclear Power Plants.
3.10 The leakage extraction of the packing
To ensure the sealing of the valve stem of the nuclear standard valve, the structure of the double-packing intermediate leakage extraction ring and leakage extraction pipe should be adopted, except for special regulations. The leakage extraction tube should be a straight tube with 10 meters and 21.3mm x 2.77mm.
3.11 Other devices
Except for electric valves, all isolation valves should be equipped with locking devices so that the valves can be locked in the open or closed position. The wedge gate valve should be designed to prevent the valve stem from rotating in the valve body to avoid damage to the sealing surface. The bolts within the pressure-bearing boundary shall be designed with mechanical locking devices.
3.12 Materials for valve parts
If the valve body is made from stainless steel, stainless steel should also be adopted for the remaining parts in contact with the conveying medium.
3.13 Interchangeability
All the same parts of the same type of valve should be interchangeable with each other.
3.14 Transportation
Valves weighing more than 30 kg should have lifting lugs, or indicate the lifting position during transportation in the figure.
4. Conclusion
According to the actual operating conditions of nuclear power valves, the technical characteristics and requirements of nuclear power valves are stricter than those of thermal power and hydropower valves. In addition to the technical requirements of conventional valves, finite element analysis and seismic calculation analysis are also required, the limit calculation of the primary film stress, the limit calculation of the primary film stress plus bending stress, and the circuit start-stop cycle-related calculation of the limit calculation of the amplitude of the primary and secondary stress changes and the design of the stuffing box's anti-leakage structure are also required. Pollution of impurities in the medium, ambient temperature, operating temperature, ambient humidity, radioactive DC power supply and voltage fluctuations, and stable technical requirements under related earthquake and vibration conditions and safety levels should also be considered.
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Previous: Design Requirements for Main Parts of Nuclear Power Valves (Part Two)