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1. Introduction

2. Structure and Working Principle of Bellow Globe Valves

2.1 Core Structural Components

2.2 Working Principle

1. Opening Process: Rotate the handwheel counterclockwise or activate the electric actuator. The valve stem moves upward, the bellows is stretched, the valve disc leaves the valve seat, the fluid channel opens, and the medium can pass through the valve.
2. Closing Process: Rotate the handwheel clockwise or deactivate the electric actuator. The valve stem moves downward, the bellows is compressed, the valve disc is pressed tightly against the valve seat, and the sealing surface forms a tight contact to prevent fluid from passing through.

2.3 Operational Characteristics and Advantages

1. Zero Leakage Sealing: The metal bellows provides an absolute sealing barrier, completely eliminating the possibility of valve stem leakage. It is particularly suitable for applications involving toxic, flammable, explosive, or valuable media.
2. High-Temperature and High-Pressure Resistance: The metal bellows can withstand high-temperature (up to 425°C) and high-pressure (up to 2500LB) environments, while maintaining excellent sealing performance under extreme conditions.
3. Long Service Life: The fatigue life of the bellows is usually tens of thousands of cycles or more, much longer than that of the traditional packing sealing structure, reducing maintenance frequency and downtime.
4. Low Maintenance Requirements: There is no need for regular adjustment or replacement of packing, greatly reducing maintenance workload and costs.
5. Korrosionsbeständigkeit: Selecting appropriate materials (such as 316L, Inconel, etc.) can resist corrosion from various corrosive media.
6. Precise Control: The linear deformation characteristics of the bellows enable the valve to have excellent flow regulation performance, suitable for occasions requiring precise control.
7. High Safety: Eliminates the risk of external leakage, improving system safety, especially suitable for application scenarios with high safety requirements.

3. Application Fields of Bellow Globe Valves

3.1 Petroleum and Natural Gas Industry

1. Oil and Gas Extraction: In wellhead devices and Christmas tree systems, bellow globe valves are used to control the flow of high-pressure oil and gas, ensuring safe extraction.
2. Oil and Gas Processing: In oil and gas separation, desulfurization, dehydration, and other processing processes, they are used to control the flow of corrosive media.
3. Pipeline Transportation: In oil and gas pipeline systems, they are used for pressure regulation, flow control, and emergency shutdown.
4. Oil Refining and Chemical Engineering: In oil refineries and petrochemical plants, they are used to control the flow of various petroleum products and chemical raw materials.

3.2 Power Industry

1. Thermal Power Plants: In steam systems, feedwater systems, and condensate systems, they are used to control the flow of high-temperature and high-pressure steam and water.
2. Nuclear Power Plants: In nuclear reactor coolant systems and auxiliary systems, they are used to control high-temperature, high-pressure, and radioactive media, ensuring safe system operation.
3. Renewable Energy: In renewable energy systems such as solar energy, geothermal energy, and biomass energy, they are used to control the flow of various media.

3.3 Chemical and Pharmaceutical Industries

1. Chemical Production: At the inlets and outlets of various chemical reactors, distillation towers, storage tanks, etc., they are used to control corrosive, toxic, flammable, or explosive media.
2. Pharmaceutical Production: In the pharmaceutical production process, they are used to control high-purity, sterile, or toxic media, meeting GMP requirements.
3. Fine Chemicals: In the production process of fine chemical products such as dyes, coatings, and cosmetics, they are used for precise flow and pressure control.

3.4 Other Application Fields

1. Food and Beverage: In the food and beverage production process, they are used to control the flow of various liquid raw materials and products, meeting hygiene requirements.
2. Water Treatment: In water treatment systems, they are used to control the addition of various chemical agents and the flow of water.
3. Shipbuilding: In the power systems, cooling systems, and ballast water systems of ships, they are used to control the flow of various media.
4. Aerospace: In the hydraulic systems and fuel systems of aircraft and spacecraft, they are used to control the flow of various fluids.

4. Common Failure Modes of Bellow Globe Valves

4.1 Bellows-Related Failures

1. Fatigue Cracks: Long-term cyclic expansion and contraction lead to metal fatigue, and cracks are prone to occur at the root or weld of the bellows. The fatigue life of the bellows is usually related to the material, wall thickness, corrugation shape, and working conditions. When the working pressure fluctuates frequently or the amplitude is large, the fatigue life will be significantly reduced.
2. Corrosion Perforation: Corrosive media (such as acid, alkali, and salt solutions) react chemically with the bellows material, causing the material to be gradually eroded and form small holes or perforations. Pitting corrosion, crevice corrosion, and stress corrosion cracking are common forms of corrosion. Especially in environments containing chloride ions, stainless steel bellows are prone to stress corrosion cracking.
3. Overload Deformation: Improper operation (such as excessive force during manual operation) or abnormal system pressure causes the bellows to be overstretched or compressed, exceeding its elastic limit and resulting in permanent deformation. This will lead to a decrease in sealing performance or even complete failure.
4. High-Temperature Aging: In a long-term high-temperature environment (such as exceeding 300°C), the elasticity of the metal material gradually decreases, the bellows becomes brittle, and cracks are prone to occur.
5. Welding Defects: Defects (such as air holes, incomplete fusion, cracks, etc.) exist at the welding position of the bellows with the valve stem or valve cover. These defects may expand during use, leading to leakage.
6. Mechanical Damage: Improper operation during installation or maintenance may cause scratches or dents on the bellows surface. These damages will become stress concentration points, accelerating the formation of fatigue cracks.

4.2 Sealing Pair Failures

1. Sealing Surface Wear: Frequent opening and closing operations or solid particles in the medium cause wear on the sealing surface, reducing the sealing performance. Wear usually manifests as scratches, pits, or uneven wear on the sealing surface.
2. Sealing Surface Corrosion: Corrosive media react chemically with the sealing surface material, causing the material to be eroded and forming pits or corrosion grooves.
3. Sealing Surface Deformation: In a high-temperature environment, the sealing surface material may creep or deform, leading to a decrease in sealing performance.
4. Medium Crystallization or Precipitation: After the valve is closed, some media may crystallize or precipitate on the sealing surface, making it impossible to completely close the valve or difficult to open again.
5. Sealing Surface Damage: Improper installation or foreign objects entering the valve may cause damage to the sealing surface, forming scratches or pits and affecting the sealing performance.

4.3 Actuation and Transmission Mechanism Failures

1. Valve Stem Jamming: The gap between the valve stem and the guide sleeve is too small, insufficient lubrication, or corrosion causes the valve stem to be blocked during movement.
2. Valve Stem Bending: Excessive operating force or improper installation causes the valve stem to bend, affecting the normal opening and closing of the valve.
3. Thread Wear: The connecting threads between the valve stem and the handwheel or actuator are worn due to frequent operation or insufficient lubrication, leading to a decrease in transmission efficiency or inability to transmit torque.
4. Actuator Failures: The motor burnout and control board damage of the electric actuator, and the diaphragm rupture and cylinder air leakage of the pneumatic actuator will cause the actuator to fail to work normally.
5. Limit Switch Failures: The limit switch of the electric actuator malfunctions, causing the valve to fail to correctly indicate the fully open or fully closed position, and even causing over-travel damage.

4.4 Other Failures

1. Packing Box Leakage: Although the bellows is the main sealing element, some designs still retain the packing box as an auxiliary seal. If the packing ages or is improperly installed, it may cause leakage.
2. Valve Cover or Valve Body Leakage: Problems occur at the connection and sealing position (such as gaskets, bolts) between the valve cover and the valve body, causing medium leakage.
3. Valve Vibration: Excessively high fluid flow rate or improper valve opening may cause valve vibration, affecting the service life and generating noise.
4. Medium Backflow: In globe valves with check valve functions, damage to the sealing surface may cause medium backflow, affecting the normal operation of the system.

5. Maintenance Methods and Technologies for Bellow Globe Valves

5.1 Daily Inspection and Maintenance

1. Visual Inspection: Regularly check whether there are leakage traces, corrosion, or mechanical damage on the external part of the valve. Pay special attention to whether there are cracks, deformation, or corrosion signs on the bellows surface.
2. Operation Inspection: Check whether the opening and closing operation of the valve is smooth, and whether there is jamming or abnormal resistance. Pay attention to whether the operating torque increases significantly, which may be a sign of sealing surface wear or valve stem jamming.
3. Leakage Detection: Use leak detection instruments or soapy water to check whether there is leakage at each sealing part of the valve. Pay special attention to the bellows part and the valve cover connection.
4. Temperature Inspection: In a high-temperature environment, use an infrared thermometer to check whether the temperature of each part of the valve is normal and whether there are abnormal hot spots.
5. Pressure Inspection: Check whether the pressure before and after the valve is normal, and whether there are abnormal pressure fluctuations or pressure drops.
6. Recording and Analysis: Establish a valve maintenance file, record the inspection results and abnormal situations, analyze the change trend, and timely detect potential problems.

5.2 Bellows Maintenance and Replacement

1. Bellows Inspection: Regularly check whether there are cracks, deformation, corrosion, or mechanical damage on the bellows surface. For concealed bellows, tools such as endoscopes can be used for internal inspection.
2. Non-Destructive Testing: Regularly perform non-destructive testing on the bellows, such as magnetic particle testing, penetration testing, or ultrasonic testing, to detect internal defects or cracks.
3. Overload Prevention: Operate the valve in strict accordance with the operating procedures to avoid excessive force or over-pressure operation, and prevent overload deformation of the bellows.
4. Medium Control: Control the content of solid particles in the medium. If necessary, install a filter upstream of the valve to prevent particles from entering the valve and wearing the bellows or sealing surface.
5. Temperature Control: Avoid long-term operation of the valve in an environment exceeding the design temperature to prevent aging of the bellows material.

• Obvious cracks or corrosion perforations appear on the bellows surface
• The bellows has permanent deformation and cannot be restored
• Leakage is found in the bellows leakage test
• The expansion and contraction performance of the bellows decreases significantly
• The fatigue life of the bellows is close to the design life

5.3 Sealing Pair Maintenance and Repair

1. Sealing Surface Inspection: Regularly check whether there are wear, corrosion, scratches, or other damages on the sealing surface. For important valves, a high-power magnifying glass or endoscope can be used for detailed inspection.
2. Cleaning Treatment: Regularly clean the sealing surface to remove medium residues, crystals, or sediments, and prevent these substances from affecting the sealing performance.
3. Dry Grinding Prevention: Avoid frequent operation of the valve in the absence of medium to prevent accelerated wear of the sealing surface due to dry grinding.
4. Lubrication Maintenance: According to the medium characteristics, select a suitable lubricant to regularly lubricate the sealing surface, reduce friction and wear. For special industries such as food and medicine, a lubricant that meets hygiene requirements should be used.

1. Grinding Repair: Use grinding tools and grinding paste to grind the sealing surface, remove surface defects, and restore the sealing performance. During the grinding process, attention should be paid to controlling the grinding amount to avoid excessive grinding resulting in thinning of the sealing surface.
2. Overlay Welding Repair: For sealing surfaces with severe wear, overlay welding can be used for repair. Select a suitable welding rod according to the original sealing surface material, and process and grind after overlay welding.
3. Spraying Treatment: Use thermal spraying technology to spray wear-resistant and corrosion-resistant materials on the sealing surface to improve the performance and service life of the