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Last updateFri, 02 Dec 2016 4pm

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Valves in a Cement Slurry Line

Valves in a Cement Slurry Line

Basically everywhere you look in modern ...

Triple Offset Butterfly Valves

Triple Offset Butterfly Valves

Since their introduction to the market m...

Digital Valve Control Leads to Increased Plant Availability

Digital Valve Control Leads to Increased Plant Availability

Surge is characterized by fast flow reve...

Cast vs. Forged: The Ongoing Debate Takes a New Direction

Cast vs. Forged: The Ongoing Debate Takes a New Direction

In the valve industry, the cast versus f...

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Industry Headlines

Industry Headlines

VMA Members Among Plant Engineering 2016 Product of the Year Finalists

2 DAYS AGO

Several VMA members are among this year’s Plant Engineering Product of the Year finalists. Emerson has products nominated in four different categories, while Siemens has several products nominated in a total of three different categories. Chesterton and Hunt Valve have products up for awards the...

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MSS Publishes Revised American National Standard for Steel Pipeline Flanges and Receives ANSI Approval

3 DAYS AGO

The Manufacturers Standardization Society (MSS) announces that the substantially revised Standard Practice, SP-44-2016, Steel Pipeline Flanges, has been approved by the American National Standards Institute (ANSI) as a Revised American National Standard (ANS).

The first edition of MSS SP-44 was publish...

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U.S. Chemical Industry Remains Optimistic for 2017

2 DAYS AGO

Moving into 2017, the U.S. Chemical Processing Industry continues to enjoy optimism about future investment, according to Industrial Info's 2017 Global Industrial Outlook . Much of this activity stems from the continued low cost of natural gas liquids (NGLs), a primary feedstock for building-block che...

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Hydraulic Institute Celebrates Centennial with New Logo

3 DAYS AGO
Hydraulic Institute Celebrates Centennial with New Logo

The Hydraulic Institute (HI) will celebrate its centennial in 2017 with a new logo as part of a larger initiative to position HI for the next 100 years of service to the pump industry. The new logo is a key element of HI’s overall brand refresh and redesign process.

The logo includes a hidden &ld...

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U.S. Adds 178,000 Jobs, Unemployment Rate at 4.6%

1 DAY AGO

The unemployment rate declined 0.3% to 4.6% in November, and total nonfarm payroll employment increased by 178,000, the Department of Labor reported today. Employment gains occurred in professional and business services and in health care.

Employment in construction continued on its recent upward trend...

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Third Quarter GDP Revised Up to 3.2% Growth

3 DAYS AGO

Gross domestic product (GDP) in the U.S. increased at an annual rate of 3.2% in the third quarter of 2016, according to the second estimate released by the Department of Commerce. In the second quarter, real GDP increased 1.4%.

This new GDP estimate is based on more complete source data than were avail...

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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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