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Last updateTue, 31 May 2016 7pm

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The Limits of Standard Manual Globe Valves for Throttling

The Limits of Standard Manual Globe Valves for Throttling

A common practice in process services is...

Industry and Regulatory Changes in Offshore Operations

Industry and Regulatory Changes in Offshore Operations

On May 13, 2016, the offshore oil and ga...

Strategies for Successful SIS Valve Diagnostic Implementation

Strategies for Successful SIS Valve Diagnostic Implementation

End users and contractors alike strive t...

Stop Check Valves

Stop Check Valves

Stop check valves are vital to several i...

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Industry Headlines

Additive Manufacturing Industry Hit $5.1 Billion in 2015

6 HOURS AGO  |  Chris Guy

According to Wohlers Report 2016, the additive manufacturing (AM) industry, consisting of all AM products and services worldwide, grew 25.9% (CAGR) to...

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Industry Headlines

Weir Opens New Safety Relief Valve Facility in Malaysia

1 DAY AGO

Weir has opened a new facility to increase the global reach and competitiveness of Weir valves by establishing a manufacturing and assembly plant close to Malaysia’s capital Kuala Lumpur.

The Malaysian operation has already successfully supplied several large and strategic projects, especially ...

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ValvTechnologies Names Garcia, Mermelstein to New Positions

6 DAYS AGO
ValvTechnologies Names Garcia, Mermelstein to New Positions

ValvTechnologies, Inc. has named David Garcia director of manufacturing and Steve Mermelstein as regional director, Americas and director, channel management.

Previously, West Point graduate Garcia served as director of operations for Merla Wellhead Solutions and held plant manager positions at Hallib...

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What’s Behind Growth of U.S. Natural Gas Use

6 HOURS AGO

U.S. consumption of natural gas is projected to rise from 28 trillion cubic feet (Tcf) in 2015 to 34 Tcf in 2040, an average increase of about 1% annually, according to EIA's Annual Energy Outlook 2016 . The industrial and electric power sectors make up 49% and 34% of this growth, respectively, while ...

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Industry Survey Finds U.S. Wind Power on the Rise

6 HOURS AGO

Wind power, America’s fastest growing new source of electricity, will stay on pace to grow to supply 10% of U.S. electricity by 2020, that’s according to the American Wind Energy Association (AWEA). Helping to grow wind energy in the U.S. are a mix of stable federal policy, passed late las...

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Additive Manufacturing Industry Hit $5.1 Billion in 2015

6 HOURS AGO

According to Wohlers Report 2016, the additive manufacturing (AM) industry, consisting of all AM products and services worldwide, grew 25.9% (CAGR) to $5.165 billion in 2015. The CAGR for the previous three years was 31.5%. Over the past 27 years, the CAGR for the industry is 26.2%. Wohlers Associat...

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Second Quarter GDP Forecast Points to 2.9% Increase

10 HOURS AGO

The Atlanta Federal Reserve’s GDPNow model forecast for real GDP growth in the second quarter of 2016 is 2.9% on May 26, up from 2.5% on May 17. The forecast for second-quarter real gross private domestic investment growth increased from -0.3% to 0.4% following this morning's durable manufacturi...

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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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