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Unique Operating Dynamics of Trunnion-Mounted Ball Valves

Unique Operating Dynamics of Trunnion-Mounted Ball Valves

For a very long time, the idea has exist...

Adopting the IIoT: Are Results Matching the Hype?

Adopting the IIoT: Are Results Matching the Hype?

Many valve, actuator and control manufac...

Where Valves Are Used: Everywhere!

Where Valves Are Used: Everywhere!

Valves can be found just about anywhere ...

Oxygen Cleaning: A Validated Process is Critical for Safety

Oxygen Cleaning: A Validated Process is Critical for Safety

From time to time, we re-publish well-re...

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Industry Headlines

Conference Board Economic Index Rose in October

Tuesday, 21 November 2017  |  Chris Guy

The Conference Board Leading Economic Index (LEI) for the U.S. increased 1.2% in October to 130.4 (2010 = 100), following a 0.1% increase in September...

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Industry Headlines

VanAire Celebrates Manufacturing with ‘Industry After Hours’

1 DAY AGO
VanAire Celebrates Manufacturing with ‘Industry After Hours’

On Nov. 8, Delta County, MI K-12 students and parents attended Industry After Hours at VanAire to learn more about the high tech, high skilled manufacturing jobs that are available. Over 276 participants were treated to a fun, entertaining and informative event that exceeded expectations and inspired ...

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Emerson Opens Solutions Center in Singapore

3 DAYS AGO

As part of its drive to make Singapore a hub for the delivery of Industrial Internet of Things (IoT) technologies and services for customers across Asia Pacific, Emerson opened a customer-focused Solutions Center at the regional headquarters of its Automation Solutions business in Singapore. To mark...

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Nebraska Approves Keystone XL Pipeline Route

1 DAY AGO

By a vote of 3-2, the Nebraska Public Service Commission approved an order giving TransCanada the go ahead to build the Keystone XL Pipeline utilizing the proposed Mainline Alternative Route. This is one of three proposed routes included in the application filed by TransCanada Keystone Pipeline. L.P...

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Energy Outlook Shows a World in Transformation

7 DAYS AGO

The resurgence in oil and gas production from the United States, deep declines in the cost of renewables and growing electrification are changing the face of the global energy system and upending traditional ways of meeting energy demand, according to the World Energy Outlook 2017 . A cleaner and more...

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Conference Board Economic Index Rose in October

3 HOURS AGO

The Conference Board Leading Economic Index (LEI) for the U.S. increased 1.2% in October to 130.4 (2010 = 100), following a 0.1% increase in September, and a 0.4% increase in August.

“The U.S. LEI increased sharply in October, as the impact of the hurricanes dissipated,” said Ataman Ozyildi...

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U.S. Industrial Output Up 0.9% in October

4 DAYS AGO

Industrial production rose 0.9% in October, and manufacturing increased 1.3%. The index for utilities rose 2.0%, but mining output fell 1.3%, as Hurricane Nate caused a sharp but short-lived decline in oil and gas drilling and extraction. Even so, industrial activity was boosted in October by a return...

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Ball Valves in Power Plants

vmwnt12_nuclear_plantCan metal-seated ball valves provide effective long term, economical solutions for critical applications in steam-generating power plants? The answer lies in knowing the design limitations of the valve, in correctly identifying the application requirements and in proper installation techniques.

During the last 20 years, advances in machining, tooling, measuring and coating technology have led to ball valve designs that provide positive sealing solutions for the power industry. These new “power plant ball valves” can withstand temperatures and pressures that make them a viable solution for the industry.


THE HISTORY

Before these new designs, creating true and matching spherical sealing surfaces was limited so that one surface—the ball—typically was metal and highly polished. The second sealing surface—the seat—generally was a fluoropolymer or elastomeric compound. This combination works well in lower temperatures and pressures, and still is widely used today. However, it is not suited for the extremes seen in steam power generating stations.

vmwnt12_Figure-1Figure 1. Typical Y-pattern globe valveInstead, traditionally rising-stem globe valves have been the work horses for stop and isolation service in steam-generating power plants (Figure 1). These valves have massive stems, plugs and seats. They are top-entry valves and often have welded or pressure seal bonnets.

The sealing areas of the plug and seat are matched conical surfaces, which are well-suited for the high pressures, temperatures and velocities found in vent, drain and continuous process services. Operation of the valves is intuitive: If the stem is in the “up” position, the valve is open; if the stem is in the “down” position, the valve is closed.


METAL-SEATED BALL VALVES

Computer numerically controlled (CNC) machines with special tooling can now produce virtually perfect spherical metal-to-metal sealing surfaces—both concave, and convex for ball and seat—with almost infinite repeatability. Highly qualified and specialized coating contractors also can provide many varieties of flame-sprayed carbide coating compounds applied with exacting precision in laboratory conditions by CNC robotic machines. These coatings carry a toughness and hardness far exceeding that of the cobalt-based weld overlays traditionally used in rising stem globe valves, and the final coated surface exactly mirrors the machined contours of the underlying part. These technologies have lead to the emergence of the power plant ball valve, capable of withstanding temperatures in excess of 1050° F (566° C) and ­pressures in excess of 3000 psig.


CONSTRUCTION FEATURES

Many power plant ball valve manufacturers are machining valve bodies from forged bar stock materials with massive wall thicknesses far exceeding that of rising stem valves. Several use the same valve body design on 1.5-inch and smaller sizes for all pressures classes—so that an ASME Class 1500 valve may actually have an ASME Class 4500 body. This standardization reduces raw material inventory, streamlines machining, shortens production times and allows for virtually unlimited alloy material selection. Usage is restricted by the pressure and temperature rating stated on the original equipment manufacturer (OEM) tag and relevant American Society of Mechanical Engineers (ASME) and American National Standards Institute (ANSI) standards.

vmwnt12_Figure-2Figure 2. Two-piece end-entry design

 

vmwnt12_Figure-3Figure 3. One-piece end-entry design

vmwnt12_Figure-4Figure 4. Top-entry designValve manufacturers produce a ­variety of power plant ball valve body designs, including two-piece end entry (Figure 2), one-piece end entry (Figure 3) and bolted bonnet top entry (Figure 4). Different seat designs are produced: integral seat, pressed-in seat, welded seat and locked seat. All designs incorporate a downstream sealing seat, with an upstream ring used as a guiding, balancing and bearing surface.

vmwnt12_Figure-5Figure 5. Live-loading methodThese designs all include a large cross-section conical load spring (Belleville washer) behind the upstream bearing ring. The designs feature live-loaded stem packing, although several methods provide this live-loading (Figure 5). Some use one large central Belleville spring, while others use four, equally spaced spring sets. Packing design varies among manufacturers—some use a single die-formed ring with wire-braided backup while others use multiple die-formed rings, and still others use top- and bottom-braided rings with internal die-formed rings.

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