Metal seated ball valves
Metal-seated ball valves face significant challenges in maintaining integrity and functionality under high-pressure conditions . This article explores innovative solutions to overcome these issues , with a focus on the flexible groove design concept .
Flexible grooves combat ball valve deformation challenges
By Amutha Geethan
About the author Amutha Geethan is a Design Manager at PTPA Middle East FZE with 13 years of experience in valve design and development . A Mechanical Engineering graduate , Amutha has specialized in ball valve design for various applications , including cryogenic , hightemperature and subsea environments , with 2 years of R & D experience specifically in cryogenic valve development .
Valve seat sealing in metal-to-metal seated ball valves poses a significant challenge in maintaining valve integrity and functionality , particularly under high-pressure conditions ( from ANSI class 1500 and from API 5000 PSI ). A typical trunnionmounted ball valve relies heavily on the correct sizing of the ball to ensure static strength and prevent leakage . This article examines ball sizing , common issues and innovative solutions to address these challenges .
The importance of ball sizing
In metal-to-metal seated ball valves , the ball ’ s size is crucial for maintaining static strength and preventing leakage . An undersized ball can lead to elastic deformation , commonly known as the “ egging effect ,” where the ball deforms into an elliptical shape under pressure . This deformation is particularly problematic at the 3 and 9 o ’ clock positions , leading to leakage due to insufficient contact pressure between the ball and the seat .
Understanding the egging effect
The egging effect occurs when the ball ’ s material undergoes elastic deformation due to the pressure exerted during valve operation . As a result , the ball loses its perfectly spherical shape , compromising the seal integrity . This deformation is more pronounced at the 3 and 9 o ’ clock positions , where the ball seat contact is weaker due to the smaller thickness near these points . Figure 1 illustrates the egging effect and the resultant leakage paths .
Sizing rules and pressure considerations
Valve designers often use a rule-of-thumb approach , considering the sphere-to-ball ratio for various pressure ranges . This method involves verifying the contact pressure between the ball and the seat using finite element analysis ( FEA ). The criterion for a successful seal is that the contact stress generated must exceed the line pressure to ensure valve tightness . However ,
Figure 1 as the pressure rating increases , the ball size must also increase significantly to counteract the egging effect , leading to bulkier and more complex valve designs .
Perfect lapping technology
Perfect lapping technology can achieve a tight shut-off by ensuring an exceptionally smooth and accurate ball-seat interface . However , even with perfect lapping , under sizing the ball will still cause leakage due to insufficient contact pressure to counteract the deformation under operational conditions .
Material constraints in valve industry
The choice of materials in the valve industry is limited due to the need to balance strength and durability with resistance to cracking or brittle failures . Harder materials , while offering increased resistance to deformations , pose a higher risk of cracking under some chemical services like H2S . This limitation further complicates the task of ensuring a reliable seal , as designers must work within the constraints of available materials that can endure the mechanical stresses without compromising the valve ’ s integrity .
Innovative solutions for enhanced sealing
To address the limitations of traditional ball sizing methods , valve manufacturers have developed innovative technologies and alternative designs to improve sealing performance without significantly increasing ball size .
Cameron ’ s Integrated Sealing Technology ( IST )
Cameron , a valve manufacturing company , introduced the Integrated Sealing Technology ( IST ) as a solution to the egging effect and leakage issues in high-pressure applications . IST involves a specialised ball and seat design that enhances the contact pressure and ensures a tight seal even under extreme conditions . The technology focuses on optimising the ball-seat interface to prevent deformation and maintain consistent sealing performance .
Flexible groove design
An alternative solution to the egging effect is the introduction of a flexible groove in the ball ( Figure 2 ). This approach offers significant advantages in sealing performance . The flexible groove design allows for localized flexibility in the ball-seat contact region , effectively absorbing
68 Valve World November 2024 www . valve-world . net