07222017Sat
Last updateFri, 21 Jul 2017 2pm

i

Monitoring Valve Health via the Internet

Monitoring Valve Health via the Internet

Most valve end users are already using s...

Valves in Oxygen Service

Valves in Oxygen Service

In his presentation at VMA’s 2017 ...

Thermal Spray Coating

Thermal Spray Coating

Q: What are the pros and cons of us...

Ball Valve Repair 101

Ball Valve Repair 101

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

Subscribe SUM17

FREE SUBSCRIPTION*

•  Print magazine
•  Digital magazine
•  VALVE eNews
Read the latest issue

*to qualified valve professionals in the U.S./Canada

The Weekly Report

New Products

  • ja-news-2
  • ja-news-3

Industry Headlines

LyondellBasell to Build the World's Largest PO/TBA Plant

Friday, 21 July 2017  |  Chris Guy

LyondellBasell has made the final investment decision to build the world's largest propylene oxide (PO) and tertiary butyl alcohol (TBA) plant in the ...

Readmore

Loading...
Advertisement
i

Web Only

How to Choose the Best Rapid Prototyping Method

How to Choose the Best Rapid Prototyping Method

Tuesday, 18 July 2017  |  Kate Kunkel

As new products are designed, including valve bodies and the parts that comprise the finished valve, prototypes must be created. How that is achieved ...

Readmore

Loading...

Industry Headlines

Badger Alloys Joins VMA as Associate Member

3 DAYS AGO

This week the Valve Manufacturers Association (VMA) welcomes Badger Alloys as an official associate supplier member. This is VMA’s fourth new member in 2017.

Located in the heart of Milwaukee and founded in 1966, Badger Alloys offers single source capabilities for custom castings. The company pou...

Readmore

Thermodyn Joins VMA as Associate Member

3 DAYS AGO

This week the Valve Manufacturers Association (VMA) welcomes Thermodyn Corporation as an official associate supplier member. This is VMA's third new member in 2017.

In 1979, Thermodyn began business with the dual purpose of selling A.W. Chesterton products and manufacturing high-temperature elastomers ...

Readmore

LyondellBasell to Build the World's Largest PO/TBA Plant

17 HOURS AGO

LyondellBasell has made the final investment decision to build the world's largest propylene oxide (PO) and tertiary butyl alcohol (TBA) plant in the Houston area. The project is estimated to cost approximately $2.4 billion, representing the single-largest capital investment in the company's history...

Readmore

EPA Selects Projects for Water Infrastructure Loans

1 DAY AGO

The EPA is inviting 12 projects in nine states to apply for Water Infrastructure Finance and Innovation Act (WIFIA) loans. These potential applicants were selected from a group of projects that represent large and small communities from across the U.S. that submitted letters of interest to EPA in Ap...

Readmore

Leading Economic Indicators Increased in June

17 HOURS AGO

The Conference Board Leading Economic Index (LEI) for the U.S. increased 0.6% in June to 127.8 (2010 = 100), following a 0.2% increase in May, and a 0.2% increase in April.

“The U.S. LEI rose sharply in June, pointing to continued growth in the U.S. economy and perhaps even a moderate improvement...

Readmore

U.S. Jobless Claims Fall to Near Five-Month Low

1 DAY AGO

In the week ending July 15, the advance figure for seasonally adjusted initial claims was 233,000, a decrease of 15,000 from the previous week's revised level. The previous week's level was revised up by 1,000 from 247,000 to 248,000. The 4-week moving average was 243,750, a decrease of 2,250 from t...

Readmore

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.

  • Latest Post

  • Popular

  • Links

  • Events

Advertisement

Looking for a career in the Valve Industry?

ValveCareers Horiz

To learn more, watch the videos below or visit ValveCareers.com a special initiative of the Valve Manufacturers Association