Metal Seated Ball Valve 

What is a metal seated ball valve? 

Metal seated ball valves are valves designed with metal to metal seal between the ball and the seats. Metal seated ball valves are meant for use in applications of corrosion, abrasion, high pressure, or high temperature. Metal seated ball valves enhance a tight shutoff in both bi and unidirectional fluid flow in severe applications. Metal seated ball valves can be made harder by coating them for example with ultrasonic spray coating, chromium carbide, satellite hard facing, and tungsten carbide. Metal seated ball valves use metallic material like 316 stainless steel or Monel to make the valve seat. Most ball valves use soft seats made of thermoplastics like PTFE which are meant for clean service only unlike metal seated ball valves. Metal seated ball valves have remained among the best solutions to severe service applications. Each type of metal seated ball valve has its characteristics which yields unique advantages and disadvantages. 

Components of a metal seated ball valve 

Valve body 

The valve body is the component of a metal seated ball valve which covers the internal components of the valve. The body helps to enhance safety to the interior parts. The body contains the ports where the fluid enters and exits the metal seated ball valve. The body needs to be strong so that it can provide a reliable barrier to fluid pressure.

Bonnet 

The bonnet is the part of a metal seated ball valve which is used to cover the stem and packing. Bonnet enhances safety to the packing and stem. Bonnet is placed on top of the valve body and the two are connected through welding or using bolts and nuts. The bonnet is made of the same metallic material as the valve body. 

Actuator 

The actuator is a component integrated into the automatic metal seated ball valve to provide the torque required to open/close the valve. With an actuator, a metal seated ball valve operator is not needed. Some of the actuators that can be used in metal seated ball valves are electric, pneumatic, and hydraulic actuators. An automatic system is used to enhance fluid control through the actuator. 

Handle 

The handle is a component used in a manual-operated metal seated ball valve. It is on the handle where the valve operator applies torque to open or close the metal seated ball valve. 

Valve ball 

This is a metallic component of a metal seated ball valve which is used to open or close the fluid flow. The ball has a hole at its center where fluid flows. 

Stem 

A stem is a shaft in a metal seated ball valve which is used to transmit the torque required to open or close the valve. The stem connects the actuator or the handle to the ball.

Seats 

Seats refer to the discs installed between the valve body and the ball. A metal seated ball valve has two seats which provide a seal between the ball and the body. The ball sits between the seats to block or allow fluid flow. There is a downstream seat mounted near the exit side and an upstream seat-mounted near the inlet side of the valve. The two seats are installed opposite to each other. 

Packing 

Packing is a seal placed on the stem to prevent fluid leakage through the stem. 

Figure: Components of a metal seated ball valve.

How does a metal seated ball valve work? 

A metal seated ball valve uses a ball with a bore at the middle section to open/close fluid flow. A metal seated ball valve works by turning the handle for a quarter turn to open or close the fluid flow. The ball of a metal seated ball valve is connected to the actuator or the handle through the stem. When the handle is rotated, the stem rotates and since it is connected to the ball the ball also rotates. To open a metal seated ball valve, the handle is rotated for a quarter turn that is 90^o in the anti-clockwise direction. This makes the stem and the ball rotate simultaneously as the handle is rotated. This makes the ball bore to be collinear with the pipeline. When the ball bore is in line with the fluid in the pipeline, then fluid flows through the valve. To close a metal seated ball valve, the handle is turned in the clockwise direction for an angle of 90^o. This makes the ball bore rotate such that it becomes perpendicular to the fluid flow. In this, the ball blocks fluid flow and thus the metal seated ball valve is said to be in a closed state. 

Figure: Working of a metal seated ball valve.

Types of metal seated ball valves

Side entry metal seated ball valve 

This is a metal seated ball valve that is assembled from its side parts. The side entry metal seated ball valve has two or three body pieces connected together. Each piece of a side entry metal seated ball valve is connected by use of bolts/stud and nuts similar to how two flanges can be connected using bolts. Side entry ball valves are made of strong metallic materials using forging method. Each piece of a side entry metal seated ball valve is made through the forging method and then they are assembled together. The forging method of making a side entry metal seated ball valve helps to minimize defects that emanate from a valve made through casting method. Side entry metal seated ball valves are easy to assemble and alignment of trim components is easy. Side entry metal seated ball valves can be opened for cleaning, inspection, repair, and maintenance which makes them long-lasting unlike other valves which are disposed of once one component breaks or which cannot be serviced or cleaned. 

Figure: Side entry metal seated ball valve.

Top entry metal seated ball valve 

The top entry metal seated ball valve is a valve that has its components assembled from the top side. This metal seated ball valve enhances trim access for cleaning, repair, and maintenance without removing the valve from the pipeline. Top entry metal seated ball valves are mostly large-sized ball valves required for high pressure and high-temperature applications. In most cases, top entry metal seated ball valves are made using the casting method to help make them free from fluid leakage. After a top entry ball valve is made through the casting method, it is taken through an NDE test to ensure it has zero defects that could emanate from the casting process. Top entry metal seated ball valves are connected to the pipeline using bolts and nuts which is an easier method of installing the valve and also enhances leakage-proof service. 

Top entry: Metal seated ball valve.

Welded body metal seated ball valve

This is a metal seated ball valve that is completely assembled through the welding method. A welded body metal seated ball valve ensures that the valve is free from leakage unlike in bolts and nuts connections which can cause leakage when the gasket is worn out. However, a welded body metal seated ball valve cannot be opened for cleaning or repair and maintenance while in the field. Welded body metal seated ball valves are used in buried or underground applications where it is not expected to do service and maintenance like in subsea applications and gas transmission. Non-destructive tests are performed on the valve body circumferential weld joints to ensure the valve does not have pores that can leak fluid. 

Figure: Welded body metal seated ball valve.

Trunnion metal seated ball valve 

This is a metal seated ball valve designed such that the ball can rotate in a fixed position. The ball in a trunnion metal seated ball valve does not move in the lateral direction as it is held in position at the bottom and at the top by a shaft known as trunnion. A trunnion metal seated ball valve creates a seal by forcing a floating metallic seat ring against the ball. The trunnion component in this metal seated ball valve absorbs pressure from the fluid flow which ensures that the contact between the seat and ball is not stressed excessively and closing/opening torque remains lower which makes it easier to open/close relative to other metal seated ball valve. A trunnion ball valve operates efficiently in a wide range of pressures which makes them suitable for numerous high-pressure applications. Operation of trunnion metal seated ball valve requires lower torque relative to other metal seated ball valves. 

Figure: Trunnion metal seated ball valve.

Applications of metal seated ball valve

• Used in the transfer of acidic products. 
• They are used in oil and gas industries. 
• Steam power plants. 
• Transfer of media with slurries. 
• Food and beverage industries. 
• Pharmaceutical industries. 
• Used in petroleum industries. 

Advantages of metal seated ball valves 

• Operate quickly. 
• Resistant to abrasion wear. 
• Resistant to corrosion. 
• High strength for high temperature and high-pressure applications. 
• Can be repaired, cleaned, and inspected which makes them last for a long time. 
• Versatile since they can be used in different industries for different applications. 
• Tight seals which are leakage proof. 

Disadvantages of metal seated ball valves

• More expensive relative to other ball valves. 
• Have cavities around the seat and ball which makes slurry solidify or block the cavity making the valve difficult to open/close.
• The drive mechanism of a metal seated ball valve must be installed vertically. 

Troubleshooting a metal seated ball valve 

Leakage when the metal seated valve is closed

• Damaged ball. Replace the ball. 
• Damaged ball seats. Replace the seats. 
• The ball is not in a fully closed position. Check the ball closed/open settings. 

Irregular ball movement 

• Foreign materials between the seat and the ball or body and the ball. Clean the seal surfaces, flush interior of the valve, and replace seats. 

Metal seated ball valve needs very high torque 

• Damaged valve seats. Use emergency seals by filling sealant to the end connection injection ports. Replace the seals and seats as soon as possible. 
• High pressure or high temperature. Ensure the metal seated ball valve is working at the recommended temperature and pressure rating. 
• Foreign materials in the metal seated ball valve. Clean the interior of the valve. 

Noisy operation or water hammer 

• Fluid is flowing at high velocity or there was an error in valve sizing. Ensure valve size matches the fluid flow. 

Stem fluid leakage 

• Loose gland cap screw. Tighten the screw. 
• Damaged stem. Replace the stem. 

Summary 

Metal seated ball valves are valves designed with metal to metal seal between the seats and the ball. Metal seated ball valves work well even in corrosion, abrasion, high pressure, and high-temperature applications. Metal seated ball valves can provide tight shut-off even in severe applications. The seat and the ball in a metal seated ball valve are made of a metallic material such as steel and or Monel.

Various types of metal seated ball valves have different characteristics and advantages. Such types of metal seated ball valves include welded body metal seated ball valves, trunnion metal seated ball valves, side entry metal seated ball valves, and top entry metal seated ball valves. Metal seated ball valves have several advantages among them quick to open/close, versatile, durable, high strength, can be opened for inspection, repair, and cleaning, ability to resist corrosion and abrasion as well as being able to provide a tight seal. Metal seated ball valves are used in various applications such as steam power plants, oil and gas, food and beverages, pharmaceuticals, agriculture, water supply among others.