08262016Fri
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Valve Basics Training Helps Fill Industry Skills Gap

Valve Basics Training Helps Fill Industry Skills Gap

One of the most keenly felt needs in tod...

An End-User’s Perspective on Valve Selection and Risk

An End-User’s Perspective on Valve Selection and Risk

I am not a valve expert, although I ofte...

New Test Stamp and More Updates on Pressure Vessel Codes

New Test Stamp and More Updates on Pressure Vessel Codes

A new test organization program and stam...

The Role of Valves in HAZOP Studies

The Role of Valves in HAZOP Studies

Process hazard analysis (PHA) is require...

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ValvTechnologies Successfully Completes NUPIC Audit

2 DAYS AGO

ValvTechnologies, Inc. recently achieved NUPIC-approved suppliers list status, upon successful completion of the Nuclear Procurement Issues Committee (NUPIC) audit conducted at the Houston facility. NUPIC members include all domestic U.S. nuclear utilities as well as several international members.

Form...

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GE Oil & Gas Supporting ONGC’s Exploratory Drilling Campaign in India

2 DAYS AGO

GE Oil & Gas has been awarded a multi-million-dollar frame agreement by Oil and Natural Gas Corporation Limited (ONGC), India’s largest exploration and production company. Under the agreement , GE will provide an estimated 55 subsea wellheads (SG5) over next three years for the operator&rsqu...

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Chemical Activity Barometer Suggests Accelerated Business Activity

3 DAYS AGO

The Chemical Activity Barometer (CAB) expanded 0.4% in August following an upward revision for July. This marks the barometer’s sixth consecutive monthly gain. Accounting for adjustments, the CAB is up 3.2% over this time last year, the strongest year over year growth since January 2015. All d...

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Innovation Could Lead to Significant Cuts in Chemical Manufacturing Energy Use

3 DAYS AGO

Scientists from ExxonMobil and Georgia Tech have developed a new technology that could significantly reduce the amount of energy and emissions associated with manufacturing plastics. If brought to industrial scale, this breakthrough could reduce industry’s global annual carbon dioxide emissions ...

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Manufacturing Productivity in U.S. Higher Than Other Nations

1 DAY AGO

“U.S. productivity unexpectedly declined for a third straight quarter in the three months through June, Labor Department figures showed. On a year-over-year basis, it fell for the first time since 2013,” Bloomberg reports .

But on a more positive note, “the U.S. still blows other natio...

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Durable Goods Orders Up 4.4%, a Six-Month High

1 DAY AGO

New orders for manufactured durable goods in July increased $9.7 billion or 4.4% to $228.9 billion, the U.S. Commerce Department announced. This increase, up following two consecutive monthly decreases, followed a 4.2% June decrease. Excluding transportation, new orders increased 1.5%. Excluding def...

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Controlling And Monitoring Control Valve Fugitive Emissions

vmsum12_fugitive_emissionsSince valves are the number one source of leakage, those faced with reducing fugitive emissions need to look at the most challenging type: control valves.

Process plant managers have a host of good reasons to minimize fugitive ­emissions from their facilities and reduce the amount of process fluid released into the atmosphere and surrounding environment. Those reasons include keeping employees and neighbors safe, lessening the facility’s environmental impact, complying with increasingly stringent air-quality regulations, optimizing the plant’s energy ­consumption and maximizing plant operating efficiency.

Industrial valves are a leading source of leakage from typical process plants. In fact, studies of refineries have shown that valves and relief valves account for about 75% of fugitive emissions.1

Because of this reality, monitoring, ­controlling and reducing valve leakage can make a significant impact on overall plant fugitive emissions. Of particular concern are control valves, which pose a greater challenge than other industrial valves because of their typical operating mode and potential leak paths. There are, however, techniques, technologies and strategies that plant owners and managers can implement to better manage fugitive emissions from the control valves in their facilities. This article highlights some of these options for typical control valve features, characteristics and options.


CONTROL VALVE LEAK PATHS

Standard control valve designs include a number of potential external leak paths. For example:

Globe-style Control Valves

vmsum12_fugitive_emissions_1Figure 1. Potential leak paths in globe-style control valvesFigure 1 shows a cross-section of a typical globe valve or linear operating valve, with the key potential leakage locations highlighted. The process fluid is contained within the valve body, which is a pressure vessel designed in compliance with standard ­pressure vessel codes, such as American Society of Mechanical Engineers (ASME), Deutsches Institut für Normung e.V. (DIN; in English, the German Institute for Standardization) or Japanese Industrial Standards (JIS).

There are several static joints or locations interfacing with the valve body where external leakage is possible, including the pipeline-flange connections and the valve-body-to-bonnet joint. Leakage at these joints is uncommon because of the static nature of these joints and the fact they are typically sealed with gaskets and then bolted together. Leakage is still possible, however, so these joints should be monitored.

The primary valve leak path is the stem-seal interface, which is typically sealed using packing installed within the valve bonnet. This is a dynamic interface, as the stem moves up and down through the packing box area during operation.

Control valves are typically applied in continuously throttling services to maintain a specific set point or operating range for different process variables, such as pressure, temperature and flow rate. As a result, the valve packing wears over time, allowing more leakage across this interface. In addition, thermal expansion and contraction caused by the process fluid and ambient temperature changes can further increase the leakage rate. Thus, the packing must be periodically tightened or fitted with some kind of mechanical compensation, such as “live loading” the packing with springs to maintain the seal integrity and control leakage to the atmosphere.

Another key contributor to packing wear in globe-style control valves—and, thus, another source of potential fugitive emissions—is the presence of foreign particles or debris in the surrounding atmosphere. Since the globe valve strokes in a linear motion, the valve stem moves up through the packing area as the valve opens and then moves back down into the packing area as the valve closes. As the valve cycles from open to close, a portion of the stem is exposed to the environment, creating an opportunity for particles to attach to the stem surface and potentially impact the packing wear rate and sealing capabilities. These particles also can increase the operating friction, which reduces the overall responsiveness and controllability of the valve.

Rotary-style Control Valves

vmsum12_fugitive_emissions_2Figure 2. Potential leak paths in rotary-style control valves Figure 2 shows a cross-section of a ­typical rotary-style or rotating-motion-design control valve. As with globe-style valves, the pipe-flange connections and the stem seal area are potential paths for process fluid to leak into the environment. However, many rotary-style ­control valves have an integrated body and bonnet, eliminating that location as a potential leak path.

A key advantage of rotary-style control valves in managing fugitive emissions is the rotating motion of the valve stem as the valve is opened and closed. The stem stays within the stem seal or packing area, minimizing the possibility of introducing foreign particles or debris into the sealing interfaces. As a result, these valves are typically more effective in reducing the possibility of fugitive emissions leakage, and normally deliver greater reliability and operating efficiency from this perspective.

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