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From Cannon Balls to Pressure Seals: Graphite for Sealing

From Cannon Balls to Pressure Seals: Graphite for Sealing

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

Gaskets Are Not Created Equal

Gaskets Are Not Created Equal

Gaskets are near the bottom of the food ...

Your Valves May Be Weaponized

Your Valves May Be Weaponized

The advent of the Internet of Things (Io...

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Industry Headlines

SVF Flow Controls Joins VMA

Friday, 22 June 2018  |  Chris Guy

This week SVF Flow Controls became a full member of the Valve Manufacturers Association (VMA). This is the fourth new VMA member in 2018 so far.

For over...

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Industry Headlines

SVF Flow Controls Joins VMA

1 DAY AGO

This week SVF Flow Controls became a full member of the Valve Manufacturers Association (VMA). This is the fourth new VMA member in 2018 so far.

For over 35 years SVF Flow Controls of La Palma, CA has been manufacturing ball valves, actuators and controls for all industrial applications.

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Emerson Wins Global Tank Storage Award

2 DAYS AGO

Emerson’s Rosemount 5900S 2-in-1 Radar Level Gauge has won the Outstanding Terminal Safety Technology Award at the 2018 Global Tank Storage Awards. This award is given to a product or technology that adds an additional layer of safety to the terminal and reduces risk to employees and the surroun...

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U.S. Specialty Chemicals Markets Continue to Gain

2 DAYS AGO

The American Chemistry Council (ACC) reported that U.S. specialty chemicals market volumes continued to gain during the second quarter, increasing 0.5% in May after an upwardly revised 1% gain in April and a 0.4% gain in March. All changes in the data are reported on a three-month moving average (3M...

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Global LNG Trade Growing, Led by Australia and the U.S.

3 DAYS AGO

Global trade in liquefied natural gas (LNG) reached 38.2 billion cubic feet per day (Bcf/d) in 2017, a 10% (3.5 Bcf/d) increase from 2016 and the largest annual volume increase since 2010, according to the Annual Report on LNG trade by the International Association of Liquefied Natural Gas Importers...

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Optimism an All-Time High in NAM Survey

2 DAYS AGO

In the latest Manufacturers’ Outlook Survey from the National Association of Manufacturers (NAM), it’s clear that businesses continue to experience highly elevated levels of activity as a result of policies like tax reform, with optimism once again breaking records —95.1% of responde...

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Texas Economy Continues to Expand at “Solid Pace”

3 DAYS AGO

The Texas economy is expanding at a solid pace. Employment has grown at a 3.6% annualized rate through May, driven by job gains in the goods-producing sector. Unemployment remains near its historical low, and labor markets are tight. The Dallas Fed’s Texas Business Outlook Surveys (TBOS) suggest...

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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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