Compact Ball Valve

Compact Ball Valves

The evolution of the Ball Valve design has not changed very much over the years, especially if we delve into the History of the design of the ball valve. There are two types of ball valve designs that primarily dominate this market, the Floating Ball valve and the Trunnion Ball valve design. Although manufacturers have produced these basic valve designs for many years, the designs have changed very little.
 
Article by Herman Ytsma
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In the early 1970’s an American company designed a floating ball valve seat carrier design that revolutionized the way floating ball valves are used in high pressure production manifold applications. The design was very robust and at the same time, was the most compact on the market. The valve incorporated the design code criteria of many popular specifications and also did away with traditional end-to-end lay lengths. The design would end up saving significant space and weight and this would set the standard for future Floating Ball Valve designs.

The valve would not meet the dimensional envelope of either API 6A nor API 6D and it would not share the published end connections associated with these valve specifications. The materials of construction were chosen from locally available bar material, that met or exceeded the design requirements in each respective valve standard.

Are we introducing a new design to you? Not at all! This valve is in service for more than 35 years in upstream, high pressure, applications. Before we will elaborate about the uniqueness of this design, we would like to take you by the hand and lead you through the three designs. The traditional Floating Ball Valve design, the Trunnion Mounted and the Compact style design. Looking at their advantages and disadvantages and compare these with each other.

1. Standard Floating Ball Valve

Traditional Floating Ball valve design

In this design the ball is able to move or “float” between the two seats. The pressure from the upstream side will push the ball into the downstream seat and will seal off the downstream seat. As line pressure is applied, the seal against the seat gets tighter and improves sealing.

Poor Low pressure sealing

The low pressure sealing capabilities of this traditional valve design are limited. Especially when the bore sizes increase and the weight of the ball becomes too much for gravity to overcome. This will prevent the line pressure from pushing the ball into the downstream seat to create an effective sealing between ball and seat.

High torque

When the pressure will increase the ball will be pushed against the downstream seat. There is no bearing that will take the load and torque will increase with higher pressure. Therefore the common application for this valve is the lower pressure application and in high pressure applications, the bore sizes are restricted to the smaller sizes.

Large ball seat interface

The ball / seat interface, or the cross section, is where the effective sealing will take place and is a relatively large surface area. The larger the cross section, the more tolerant the soft seats will be for unprocessed produced fluid media with particles. Advantages:

  • Simple design (fewer parts)
  • Large ball seat interface
  • Zero leakage rate
  • Low cost valve
  • Disadvantages
  • Poor low pressure sealing (increasing with larger bore sizes)
  • High torque in higher pressure application

2. Trunnion Mounted Ball Valves or API 6D ball valves

The trunnion mounted ball valve is very suitable for high pressure and still operate with an acceptable torque because the bearings take part of the load from the ball and seat. The low pressure sealing is excellent because both upstream and downstream seat will seal off against the ball.

The terminology double block and bleed is applicable to this design because both upstream and downstream seat will seal positive by means of a spring that energizes the seats to the ball. The design of the seats in soft seated as well as metal seated is based on a line seal, like an oring. This is an adequate sealing mechanism as long as there is no sand or debris in the fluid media. One scratch can lead to leakage. A line seal will fail as soon as there is an abrasive medium flowing through the valve. This failure will accrue especially with the soft seated design. 

A soft seated trunnion mounted valve is only suitable for clean fluid service. For abrasive media the trunnion mounted valve needs to have metals seats with tungsten carbide overlay to improve hardness against wear and tear. The disadvantage of the metal seated valve is the leakage rate. Although lapping and polishing seat and ball can reduce the leak rate of the metal to metal sealing design, there is always an acceptable leakage rate in accordance with API 598 and API6D / 6A. 

Furthermore the metal to metal contact between the ball and seat will increase the torque significant compared with the soft seated design. Advantages:

  • Excellent low pressure sealing
  • Acceptable torque in high pressure applications Disadvantages
  • Soft seated design not suitable for abrasive media
  • Complicated design with many parts.
  • Not field repairable.
  • Large design


3. The Compact Floating Ball Valve

The compact style ball valve is a floating ball valve with a seat carrier design. This seat carrier design is completely different from the traditional floating ball valve seat design. In the compact style floating ball valve, the seat carrier design, has overcome the challenges of low pressure positive shut-off and high operating torques.

High torque.
Multiple bearing surfaces

By using multiple bearing surfaces, the floating compact ball valve design is able to deal with many areas of friction, that contribute to the overall operating torque of the valve. The compact floater also incorporates a stem bearing that utilizes a step on the bearing, that acts as an axial bearing, when installed into the bonnet, which prevents the stem from cantilevering. Testing has shown that up to 50% of the overall valve torque can be found in the stem and bonnet area of the valve.

Ball / Seat interface

The ball / seat cross section ratio will remain the same even as the valve bore sizes increase. Compared to standard floating ball valves the cross section area is much larger spreading the load to an larger area and reducing friction.

In this design, the seat carrier acts as an internal bypass mechanism that equalizes pressure at the moment the valve is opened, also reducing the operating torque.

Low pressure sealing

The seat assembly with the seat carrier is energized like the trunnion valve but with an elastomeric L- seal. The seat material selection is not like traditional floating ball valves that use PTFE but an Acetal co-polymer or Peek with an elastic memory.

The floating compact ball valve seat design will seal in the low pressure applications, on the inner diameter of the seat insert, creating a line seal and sealing bubble tight, even in Helium gas testing.

In a High pressure differential application the ball is pushed in the seat (the floating principle) pushing the ball into the downstream seat will follow the full geometry of the seat insert, creating a very large ball / seat interface. This large ball / seat cross section is the difference between the soft seated API 6D trunnion ball valves and the compact floating ball valve design, that makes it possible to use this valve in unprocessed upstream fluid applications.

The compact style floating ball & seat interface is larger than any other seat design and makes this valve more tolerant of abrasive fl ow media. This valve is widely used in applications where other ball valves are not even considered, such as upstream manifolds and fracking service.

The Compact style valve is supplied together with the bevel for weld end connections. At first glance, the valve looks like a butt-weld valve. In fact the valve design has eliminated the companion flanges and welds directly to the pipe. This also offers a significant cost and weight savings to this floating compact valve design.

Just like with the flexible bore sizes, this design is an engineered item. It can be supplied to meet any material specifications that are requested. The valve can be supplied in all possible material configurations.

The biggest savings are to be realized in the Space and Weight sectors and also the variety of applications, for which it is well suited. Its original application, for High Pressure Production Manifolds has not restricted it’s use to only Off shore applications, where space and weight are always of the utmost importance. In fact due to the uniqueness of the design, with bores based off of common pipe sizes and piping materials, custom bores sizes can even be offered for piggable service applications. 

In studies performed by a major FPSO (floating production storage off shore) contractor the savings on a large turret accommodating the manifold for more than 50 risers it would save several decks on the turret just to replace the standard API 6D ball valves by high pressure compact ball valves. This would not only save major cost on the turret construction but also on the buoyancy of the FPSO.

This proven valve design comes with over 35 years of service in some of the most challenging applications. Because of these great advantages, this design is adding another option to the standard API 6D trunnion mounted ball valves and the standard API 6D floating ball valves.

The most important applications are:

  • Upstream Oil & Gas manifolds for land based and onshore installations
  • Fracking services, well completion.
  • Subsea commissioning and pre commissioning PLR’s, A&R heads etc.
  • Skid building for high pressure applications like chemical injection.
  • Diverter systems on drilling rigs.


For more information, please visit: http://combet-valves.com/

 

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