Fugitive Emissions (FE) certified valves enhance process plants’ safety

Over the past two decades, oil and gas processing facilities have been challenged with increasingly stringent regulatory and legislative requirements impacting environmental health and safety. This is particularly true of the rules governing allowable Fugitive Emissions (FE) from process valves.

These have grown enormously over the past two decades. Sources of regulation The very first broadly defined air pollution laws were enacted in the United Kingdom in the 19th century, due to concerns stemming from that country’s rapid industrialization. The same happened in the United States and Germany during the1960’s. As industrialization has progressed further, limitations have become more specific, a trend which has brought a narrower focus on fugitive emission sources, e.g. industrial valves. Numerous studies show that valves are a major source of fugitive emissionsfrom an industrial plant. Today there are several different valve-related fugitive emission standards issued by a variety of sources: 

• Normative standards (e.g. API624, FCI-91-1)• International standards (e.g. ISO 15848)• End user specifications (e.g. Shell SPE 77/312)• National legislative and regulatory agency standards (e.g. EPA 40 Parts 60/63, TA-Luft)

All of these standards have the same general purpose: to encourage and enforce compliance to the applicable local fugitive emission laws, and reduce fugitive emissions from the valves to prevent damage to health and the environment

Understanding FE standardsIt requires considerable expertise to understand the different fugitive emission standards and to use that understanding to develop valve packages that are appropriate to the processes for which they are intended, while conforming to the applicable regulatory standards.Among the most commonly used global fugitive emission standards are:

• EPA 40 Parts 60/63 (Limiting emissions to 100/500 ppmv)• TA-luft• ISO15848-1, which has been a favored standard during the recent years• Shell Oil Company’s end user specifications

Neles T5 top-entry ball valve with ND9000 intelligent valve controller.

Direct comparison of different fugitive emission standards is not straightforward due to the fact that they each rely on their own test procedures. The most important variables within these procedures are the test fluid, detection methods for leakage and limits.The test fluid may be either helium of methane. Helium is a very permeable gas and safe to use, whereas methane does not have similar permeability or safety. Due to the difference in permeability of these gases and the precautions that must be taken when using methane, leak test results are not strictly comparable. There are two methods for detecting emissions. A local method (e.g. sniffing) measures concentration which is typically associated with methane based tests (e.g. 100ppm). Sniffing can only be used as an estimate of the actual leakage. A correlation is applied to the leakage measured by sniffing to estimate actual leakage from the valve’s stem. Global methods (e.g. under vacuum) capture and accurately measure the actual leakage (e.g. mbar*l/s) into the atmosphere surrounding the valve. Because the local and global methods are so different, their results are not directly comparable.

Figure 1: Leakage value comparison of different valve fugitive emission standards. The leakage values (mbar*l/s) could be characterized better in real life leakage values indicating the leakage in liters per year for 25mm stem:

These are not the only procedural differences among the standards. Others include different testing temperatures, temperature cycles, and number of operational cycles before test data is collected. Moreover, there is flexibility in some standards to interpret test results more or less strictly. Finally, the FE limits set out by the different standards are also different.

So, how do we arrive at meaningful comparisons that will allow us to make the best choice? First, we need to take a more detailed look into the different standards to better understand the intent of their FE limitation requirements for the valve and the actual benefit of using a particular standard to evaluate fugitive emission performance.

Which FE standard is the most useful?EPA 40 Parts 60/63 sets only 100/500ppm leakage level criteria which must be met during the actual usage conditions and throughout the usage life of the valves. The leakage detection flow medium is a hydrocarbon from the pipeline, and the detection method is sniffing. The approach is very simple and clever because of the use of a process plant as the origin for fugitive emissions. Another advantage is that FE level is measured throughout the valves’ life cycle. However, hydrocarbons have different leakage behavior depending on the nature of the flow medium (gas/liquid). So it makes difficult to compare fugitive emission performance of different valves in cases of different flow mediums. Also these leakage limits are not very strict, so they are easier to fulfill. TA-Luft is a standard that requires a valve manufacturer’s designs to comply with certain requirements. 

TA-Luft sets the leakage criteria to be at bellows seal leakage level or the equivalent. The leakage detection flow medium is helium, which is a very permeable gas. Only global leakage detection methods are allowed. There are two different FE leakage level limits based on the application’s temperature level. The leakage limit for under 250°C can be regarded strict, where above 250°C limit can be regarded as less demanding. The TA-Luft standard does not define the exact number of operating cycles, so it leaves room for different interpretations. For example, should the operational life of a control valve be established at 500 or 60,000 operational cycles? In addition to that, TA-Luft does not contain a defined temperature cycle procedure, which is a slight disadvantage when evaluating a valves’ FE performance under actual usage conditions.

ISO15848-1 does not regulate the valve’s design but rather the type of approval tests with which valve manufacturers’ design must comply. The leakage detection flow medium is typically helium. Methane can be used, but such testing is uncommon due to safety concerns. ISO15848-1 has three different leakage limits which range from an extremely stringent (Class A) to a non-strict (Class C) measured with the global leakage detection methods. ISO Class A is the most demanding leakage level that exists at the moment. It is meant for valves equipped with bellows type seal packings. Quarter turn valves can reach ISO Class A leakage level in a short term, lower temperature tests with current graphite packings at the moment. This means that emission performance of current graphite packing rings greatly exceed PTFE based chevron packing rings that have been used as a fugitive emission solver in the past.

Additional benefits of current graphite packings compared to PTFE chevron packings are their fire safe properties and greatly elevated temperature range. ISO Class B leakage level can be regarded as a quarter turn valves’ performance level which can be reached with current graphite packing rings in long duration tests at a high temperature (400°C). ISO 15848 also establishes separate FE limits for a valve’s body joints (like bonnets or covers) measured by the sniffing method. There are three endurance classes for both, on-off and control valve types.

Jamesbury soft seated ball valve, series 7000.

Testing temperature classes ranging from -196°C up to 400°C may be used to define the testing temperature and compulsory temperature cycle procedure. Figure 1 summarizes allowed leakage values of different FE standards relating allowable annual leakage to the volume of everyday objects. From it we can see that ISO 15848 offers the most comprehensive leakage level classification. It does so with testing procedures that can be varied to simulate actual operating conditions. This allows the easy, quantifiable comparison of valves’ fugitive emission performance in order to select the most appropriate product for specific applications.

• ISO Class A = 0,014L per year (volume of d=3cm ball, 35% of a golf ball)• TA-Luft <250C = 0,3L per year (a soda can)• ISO Class B = 1,4L per year (~ two wine bottles)• TA-Luft =>250C = 30L per year• ISO Class C = 140L per year (~ barrel)

Accelerating the pace of ISO 15848 certificationDuring the past five years, many process industry end users have clearly begun favoring ISO 15848 emission standard as the most unified tool for measuring and realizing their FE performance objectives. This has provided a strong incentive for valve suppliers like Metso to actively pursue a wide range of theoretical and technical knowledge as well as laboratory facilities, along with the testing and reporting capabilities needed to fulfill current ISO 15848 standard’s Class A/B leakage requirements (see sidebar). The requirements of the ISO 15848 FE standard are very demanding for the valves. Here are some of the measures Metso has adopted to support them: 

• Simulating actual thermal cycling conditions: A mandatory heat cycling program simulates potential process’s heat cycling which sets high demands for the valve’s design.

For example, a weak valve design may lose its FE performance after a heat cycle. The severe heat cycling program combined with extremely low (Class A) and low leakage (Class B) limit criteria measured with accurate methods is a strong indication of low FE leakage at the harshest conditions that a valve may see during its life cycle.

• Third Party Certifications: Highly regarded 3rd party certifications are frequently obtained to verify testing conditions and actual FE performance of valves. In this way, end users can be sure that they receive high fugitive emission performance valves.

• Expanding the number of valve models tested: In 2012, a corporate initiative to increase the number of valves certified to the most stringent environmental standards was expanded to certify numerous soft- and metal-seated valves to the ISO 15848-1 standard and to translate the test results into evidence of compliance with other strict regional standards. Metso’s corporate initiative to expand and intensify FE certification coverage will continue in the future as it is the only way to provide proven, added value for the end users.

Many benefits of FE reduction Valves with low fugitive emission levels benefit end users in many ways. First, valves which have very low fugitive emissions help end users to fulfill current environmental rules and regulations which must be adhered to if the plant is to continue its operations and avoid heavy fines (which can be far more costly than FE-certified valves.)

Secondly, minimization of fugitive emissions can also avoid other costs that occur when product is lost via leaking valves. The lost flow medium results in both lost raw material and smaller endproduct yields. The more complex and processed the flow media is, the higher price it has per mass unit. The loss of flow medium is also lost energy, as the pumps or compressors must do extra work to compensate for the leakage. A considerable amount of money can be saved by minimizing fugitive emissions. FE-certified valves improve safety. A leaking packing can represent an enormous safety issue in a process plant. For example, a hydrogen leak can autoignite and cause hardly detectable flames. Such a flame will burn surroundings and compromise personnel and plant safety. Of course, health issues will also be minimized by reducing fugitive emissions. A healthier environment protects people and it also makes them more productive. For example, reducing H2S content in air allows workers to work a longer time period in high H2S content areas. By asking their valve suppliers to require FE testing to the most comprehensive standard available (currently ISO15848-1) end users can introduce significant health, safety and environmental benefits at their process plant, even as they improve their operating cost factors.

Metso’s Flow Lab

ISO15848-1 emission standard test is being prepared. Metso’s fugitive emission knowledge is based on strong in-house capabilities where fugitive emission theory and testing are combined by skilled working personnel. Metso has a new and large valve testing laboratory

where the fugitive emission development and type approval tests are done.

Metso valves reduce emissions and improve safety at processing plants 2012 was a banner year at the Metso Flow Laboratory, where a corporate initiative to increase the numbers of valves certified to the most stringent environmental emissions standards continues. In 2012, numerous Neles® metal-seated and Jamesbury® soft-seated valve products were certified to meet the requirements of the global ISO15848-1 standard, complying with many standards mandated in specific regions, including TA-Luft (Germany) and EPA 40 CFR parts 60/63 (USA). ISO15848-1 certified valves are regarded as fulfilling the most stringent emission standards, and meeting this qualification signifies compliance with many other emission standards. It is also a mandatory requirement of the majority of current projects in the oil and gas industries worldwide.Metso’s control and on-off valve product series include ball, butterfly and eccentric rotary plug valves in pressure classes ASME #150-600. In 2012, representative products from these series were shown to meet ISO15848-1 requirements for:

• Highest temperature class (+400 ºC with graphite packing) for metal seated valves and (+200 ºC with PTFE packing) for soft seated valves• Low leakage class (B)• Class A (bellows seal tightness) of the Neles D1F series cryogenic valves with graphite packing

Metso valve products minimize fugitive emissions even at high operating temperatures, meeting demands of even the harshest hydrocarbon processing plant environments. By minimizing fugitive emissions, these products help improve health and safety for workers, allowing plants to meet regulatory standards, and reduce product losses.

About the Author

Mr. Tarmo Laitinen is Technical product manager of Neles ball valves in Neles & Mapag product line. Tarmo has been working over eight years in various tasks including R&D, engineering and marketing at Metso Automation Inc.. He holds a degree (M.Sc.) in Product Development from Aalto University of Technology and almost two minors from Aalto University of Economics. He can be reached at tarmo.laitinen@metso.com

Published in Valve World magazine, July 2013 issue.