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API6D Ball Valve Types and Features

API 6D is a standard set by the American Petroleum Institute (API) for valves used in pipelines transporting oil, natural gas, and other liquids. API 6D defines the design, manufacturing, testing, and quality assurance requirements for various types of valves, including ball valves, used in these critical applications.

Types of API 6D Ball Valves

API 6D Ball Valves are designed to ensure reliability, performance, and safety in pipeline systems. There are several types of ball valves that conform to the API 6D standard:

  1. Floating Ball Valve
    • Design: In a floating ball valve, the ball is not fixed to the stem but is allowed to “float” within the valve body. It is pressed against the valve seat by the fluid pressure, ensuring a tight seal when the valve is closed.
    • Application: Suitable for low-pressure and medium-pressure systems, as the ball relies on the pressure of the fluid to create a seal.
  2. Trunnion Mounted Ball Valve
    • Design: A trunnion-mounted ball valve has a ball that is fixed at two points (top and bottom) by trunnions (supporting shafts), allowing the ball to remain stationary and only rotate. This type of valve typically requires less actuator torque than a floating ball valve.
    • Application: Suitable for higher pressure applications and large-diameter pipeline systems. Trunnion valves are generally preferred in applications where sealing performance and low torque are crucial.
      China Trunnion Ball Valve
  3. Top Entry Ball Valve
    • Design: The valve body allows for maintenance or servicing of the valve components (such as the ball and seats) through the top without removing the valve from the pipeline.
    • Application: Used in systems where easy maintenance is essential without system shutdown or disassembly.
  4. Side Entry Ball Valve
    • Design: In a side-entry ball valve, the valve body is designed such that the ball and stem assembly is inserted from the side.
    • Application: Typically used in smaller sizes and more accessible locations for easier maintenance and installation.
  5. Full Port (or Full Bore) Ball Valve
    • Design: A full port ball valve has a bore (internal diameter) that matches the pipe’s internal diameter, offering minimal flow resistance and full flow capacity.
    • Application: Ideal for applications requiring unrestricted flow, like pipelines carrying sensitive materials or substances that need to maintain flow integrity.
  6. Reduced Port (or Reduced Bore) Ball Valve
    • Design: In a reduced port ball valve, the bore is smaller than the pipe diameter. This results in some flow restriction compared to a full port ball valve.
    • Application: Typically used where space is constrained, or flow capacity is less critical.

Key Features of API 6D Ball Valves

  1. Design Pressure and Temperature Range:
    • API 6D ball valves are designed to withstand a wide range of pressures and temperatures based on the valve class. The design ratings ensure that they perform safely and effectively in both standard and extreme conditions.
  2. Material Selection:
    • The materials used in API 6D ball valves are chosen for their resistance to corrosion, erosion, and wear, as well as their ability to handle high pressures and temperatures. Common materials include stainless steel, carbon steel, and various alloys like Inconel and Hastelloy.
  3. Fire-Safe Design:
    • Fire-safe ball valves are designed to continue to operate in the event of a fire. These valves are typically equipped with secondary sealing mechanisms (e.g., graphite or metal seals) that provide sealing integrity even under high heat conditions.
  4. Blowout-Proof Stem:
    • A blowout-proof stem is a critical feature for safety. It ensures that the valve stem cannot be dislodged, even under extreme pressure, preventing accidental release of valve contents.
  5. Anti-Static Features:
    • Some API 6D ball valves are designed with anti-static features that prevent the accumulation of static electricity, reducing the risk of sparks in volatile environments.
  6. Seat Materials:
    • The valve seats are typically made from soft materials like PTFE, PEEK, or elastomers, but can also be made from metal for higher temperature or more abrasive applications. Seat designs can vary depending on the application, with options for sealing at high pressures, low pressures, or extreme temperatures.
  7. End Connections:
    • API 6D ball valves typically come with various end connections, including flanged, threaded, and welded types. Flanged ends are most common, as they allow easy installation and removal from the pipeline.
  8. Actuation Options:
    • API 6D ball valves can be manually operated (via handwheel or lever) or automatically operated (via electric, pneumatic, or hydraulic actuators). Automated actuation is often used for remote operation or in hazardous environments.
  9. Double Block and Bleed (DBB) Feature:
    • Some API 6D ball valves offer a Double Block and Bleed feature, which ensures a tight seal on both sides of the valve and allows for the safe venting of any trapped fluids between the seats. This is essential for ensuring safe maintenance and operation.

API 6D Ball Valve Applications

  • Oil & Gas Pipelines: Used extensively in the transport of crude oil, natural gas, and refined products.
  • Chemical Processing: Valves are used for the controlled flow of chemicals and other reactive fluids.
  • Water Treatment: Used to control the flow of water in treatment plants.
  • Power Generation: In power plants, ball valves regulate steam, water, and fuel in various stages of the generation process.

Summary of API 6D Ball Valve Types and Features

Type of Valve Design Features Application Areas
Floating Ball Valve Ball “floats” to create a seal, relies on fluid pressure Low to medium pressure systems
Trunnion Mounted Ball Valve Ball fixed with trunnions, lower torque required High pressure and large-diameter pipelines
Top Entry Ball Valve Servicing from the top without removing valve from pipeline Applications requiring easy maintenance
Side Entry Ball Valve Ball assembly inserted from the side Smaller systems or accessible locations
Full Port Ball Valve Full bore matching pipe diameter Unrestricted flow, sensitive materials
Reduced Port Ball Valve Bore smaller than pipe diameter Space-constrained applications

Conclusion

API 6D ball valves are designed to provide reliable, durable, and safe service in pipeline systems, especially in the oil and gas, chemical, and power generation industries. The wide variety of designs and features available ensures that these valves can meet specific operational requirements, whether dealing with high pressure, extreme temperatures, or corrosive materials

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The floating ball valve vs the trunnion mounted ball valve

‘’Floating ball’’ and ‘’trunnion ball’’ are concepts which are used generally. But what are the exact difference between these two designs and when to use which one?

The most important difference between these two design is the construction of the ball and the way in which it is assembled inside the valve body. A trunnion ball is attached and centred inside the valve body through both a top shaft -the valve stem- and a bottom shaft – the trunnion. A floating ball is attached to the valve body only through the valve stem. As a result, the floating ball ‘’floats’’ in the valve seats.

In a floating ball design the ball is pushed against the downstream seat by the in-line pressure, resulting in tightness. When operated from closed to open position, the ball is to be rotated against both the in-line pressure (∆p) and the friction of the seats. In other words: the torque needed to operate the valve is created by both in-line pressure and the nature of the valve seats. The amount of torque required increases significantly when operating pressure (∆p) and/or valve size increase, and/or whenever the nature of the seat is made more robust. The latter applies in case of a metal seated valve design.

Floating ball
Trunnion ball

In a trunnion design, the ball is inserted in a central bottom shaft which is called the trunnion. The ball is fixed between the stem and the trunnion, which inclines that the ball is not floating but fixed and centred. The inline pressure presses the seats against the ball, causing the tightness. This inclines that during operation, the ball does not have to be rotated against the in-line pressure (∆p) and the valve seats, but that is solely needs to be rotated against the pressure of the seats.

 

Floating ball & trunnion ball

As a result, the required torque of a trunnion mounted ball valve is generally lower than the torque required of a comparable floating ball valve. For example: a DN200 metal-seated floating ball valve would require a significantly larger actuator than a DN200 comparable trunnion valve, leading to significantly lower costs of the overall package. Also, in general the trunnion seat design offers higher stability which makes it more suitable for extreme conditions and especially varying pressure levels.

So, the trunnion-mounted ball valve is more suitable for high pressure applications and bigger dimensions compared to the floating ball. Another advantage of the trunnion design vis-à-vis the floating design is the fact that a trunnion generally is included with a drain or bleed connection, making it suitable to function as a dual safe device. Furthermore, it functions as an relief valve automatically whenever the pressure in the central cavity is higher than the spring force of the seats. When this happens, the seat springs relieve automatically in order to drain the excess pressure back into the main line. Because of these reasons, the trunnion is commonly used in offshore- & oil & gas applications, where extreme conditions pose the standard.

Off course, a large disadvantage of the trunnion compared to the floating design is associated with its costs; which are significantly bigger. Because of these costs, trunnions are used solely when they have to be used.

Our specialist happily assist you in advising the right ball valve design for your application.

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