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Human Factors Can Cause a Disaster—or Prevent One

Human Factors Can Cause a Disaster—or Prevent One

Process industry plants are complex and ...

Improving Valve Sealing Performance and Reliability

Improving Valve Sealing Performance and Reliability

From time to time, we are re-posting wel...

A Primer on Fugitive Emissions

A Primer on Fugitive Emissions

Fourscore and seven years ago, no one ha...

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Industry Headlines

Industry Headlines

Emerson Expanding Mississippi Facility

4 DAYS AGO

Emerson plans on delivering $500,000 in new equipment to its facility in Sherman, MS. Because of this investment , and its promise of new jobs for the region, the Sherman Economic Development Corp. has approved $150,000 in grants for Emerson.

"We have a relatively new Fisher product that will be reloca...

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REXA and CCC Form Joint Initiative

4 DAYS AGO

REXA and Compressor Controls Corporation (CCC) have formed a joint initiative to modernize steam turbine controls for enhanced performance based upon each company’s core competency.

There are more than 10,000 turbomachinery trains worldwide powered by CCC. By upgrading mechanical and hydraulic go...

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LNG Exports Expected to Drive Growth in U.S. Natural Gas Trade

4 HOURS AGO

The U.S. is expected to become a net exporter of natural gas on an average annual basis by 2018, according to the recently released Annual Energy Outlook 2017 (AEO2017). The transition to net exporter is driven by declining pipeline imports, growing pipeline exports, and increasing exports of liquefie...

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Energy Transfer Partners Building New NGL Fractionation Facility

8 HOURS AGO

Energy Transfer Partners’ subsidiary, Lone Star NGL LLC, will construct a fifth natural gas liquids (NGL) fractionation facility at Mont Belvieu, TX. The construction of Fractionator V is a result of the tremendous production growth in the Delaware and Permian Basins.

Fractionator V, including NG...

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Kansas City Fed Survey Shows Regional Manufacturing Jump

8 HOURS AGO

According to Chad Wilkerson, vice president and economist at the Kansas City Fed, the district’s February Manufacturing Survey revealed that manufacturing activity expanded further with continued strong expectations . The Federal Reserve Bank of Kansas City serves the tenth Federal Reserve Distr...

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U.S. Private Sector Growth Slows from January’s 14-Month Peak

4 DAYS AGO

At 54.3 in February, the seasonally adjusted Markit Flash U.S. Composite PMI Output Index dropped from 55.8 in January but remained above the 50.0 no-change value for the twelfth consecutive month. The latest reading signaled that private sector output growth moderated from the 14-month high recorded ...

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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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