Rahul Patil
Author: Rahul Patil
Rahul Patil is an Application Engineer (Sales support) - EMEIA providing Technical sales support to respective sales office.
This article is published on piping-world.com with the authors permission.

Numerous studies show that valves are a major source of fugitive emissions from an industrial plant. In this article, I am addressing comparison of various standards which govern Fugitive Emissions (FE) related to industrial valves. 

What is Fugitive Emission?

  • Fugitive emissions (FE) are any chemicals in a physical form that can unknowingly leak from an installation e.g. Emissions of gases or vapors from pressurized equipment like industrial valves. 
  • These are unintentional losses from equipment that arise due to normal wear and tear, improper assembly of components, damage during installation or use, vibrations, corrosion and environmental effects etc.

Valves are considered to account for approximately 60% of all fugitive emission of a Refinery out of which most emissions escape through the valve stem i.e. around 75-80%, and remaining from valve body and other joints. 

Fugitive Emissions impacting environmental health and safety, emissions of volatile organic compounds from oil refinery and chemical plants pose a long term health risk to workers and local communities. In situations where large amounts of flammable liquids and gases are contained under pressure, leaks also increase the risk of fire and explosion. Stem packing leakage in non-fugitive emissions applications i.e. steam application can be expensive because of product loss, economic losses like cleanup costs, loss of production time and labor costs to repair leaks. These scenarios demonstrate that basic packing information cannot be taken for granted and can greatly affect a plant’s safety and reliability. Reducing fugitive emissions not only protects the environment but also saves money for industrial facilities.

Poor quality valves, especially those that are used regularly but not looked after, will eventually start to leak. Often they leak along the stem (shaft) hence the focus has been on the main source of the emissions of a valve i.e. valve stem packing (gland packing).

The valve stem packing is compression packing designed to provide a seal between a moving spindle or shaft and the pressurized housing that it penetrates. Gland packing consisting of a type of gasket, is a resilient material packed under pressure so that it fills the space between the valve stem and the stuffing box and presses against both of these surfaces. Some of typical packing resilient material are based on temperature capability such as graphite (for higher temperature and fireproofing applications) or PTFE/Teflon (for excellent chemical resistance and low temperature applications). Graphite and PTFE are the main basic packing materials, usually they become selected based on fluid temperature because all materials have temperature parameters within which they work best.

Valve Fugitive Emissions

Many techniques, methods are utilized to reduce leakage at valve stem such as external springs (live loads) i.e. Belleville washers are sometimes used to ensure that proper pressure exists in the stem packing over a long period of time. This may be necessary to offset the effects of thermal expansion and consolidation. Diaphragm and pinch valves isolate the fluid from the control mechanism in a manner that avoids leaks around the stem. Bellows stem seals do not have stem leakage either.

Over the past 30 years before FE are becoming less and less tolerated by regulating agencies, since the 1990s the petroleum and chemical industries have been looking for meaningful standards that will enable the qualification of valves and packing that meet the stringent fugitive emission restrictions regulations which comes under environmental health and safety.

From last 30 years, governmental agencies have worked with industry leaders to address these leaks by increasing the implementation of new technology, new packing materials and formulations, in an attempt to reduce emission from valves. Numerous valve-related fugitive emission standards were developed which are as follows.

  • ISO 15848-1, API 622, API 624, API 641, TA LUFT (VD 2440)
  • ISO 15848-2, Shell SPE 77/312

Fugitive Emission Type Test

Valve Type Test is a protocol where upon the successful completion of the test program as defined in particular FE standard, if tested valves is qualified as per specification of FE standard then this qualification can be extended to untested sizes and classes of valves of the same type under same criteria’s which are specified in particular FE standard.

Fugitive Emission Production Acceptance Test

Valve Production Acceptance Test is a test where the Purchaser (person, group, company, agency, corporation, or designated representative responsible for valve acceptance) is going to witness actual valve evaluation test at the valve manufacturer’s site. Hence manufacturer has to perform test on each valve of required lot of purchaser or as per agreement between the manufacturer and the purchaser particular percentage of valve has been tested with a minimum of one valve of the lot of valves per valve type, pressure class and nominal size.

Even though all of these standards have the same general purpose, which is to reduce FE from the valves to prevent damage to health and the environment but the all standards are not directly comparable. They vary significantly from each other, as the test requirements, measurement methods, and approval criteria differ from one standard to another. The most important variables are the test fluid, leakage detection methods, permissible limits and acceptable criteria. ISO and API are the most commonly used global fugitive emission standards and now we arrive at the point where we can understand the meaningful comparisons between them.

Comparison of FE Standards

  • API standard does not specify the type of service for which the valve is intended, i.e. control valve service or on/off (isolating) service whereas ISO standard indicates the same in the portion of mechanical-cycles required for different services that come in valve performance endurance class.
  • ISO standard (15848-Part1 and Part 2) itself allow any type of valve motion (stem/trim travel) i.e. linear/rotary motion whereas formation of different API standards are dominantly based on valve motion i.e. API 624 for Rising Stem Valves (Linear Motion: Gate, Globe type valves) and API 641 for Quarter Turn Valves (Rotary Motion: Ball, Butterfly, and Plug type valves). All are valve-type tests meant to evaluate the total performance of the valve itself but one important point is that API 622 is not a valve test, but it provides packing test (gland/stem packing) and is applicable to graphite packing used in API 624 and API 641 qualified valves.
  • The ISO standards also defines cryogenic temperatures for testing, -46°C (-51°F) and -196°C (-320°F), whereas there are no cryogenic parameters specified in API standards. As per API 622 Packing shall be suitable for use at service temperatures –29°C to 538°C.
  • API directly includes particular fugitive emission standards in its API valve standards i.e. for multi-turn valves as per API 600 and API 602 etc. specifying that the valves shall be as per API 624 (which requires API 622 compliant packing) in order to be tagged as API 600 or API 602 valves. But the current editions of API quarter-turn valve standards (API 608, API 609) do not have API 641 certification as a requirement whereas ISO is not referenced in any of the API standards but there is chance in future that ISO-15848-Part 1 could be added as a requirement to international valve standards
  • Although methane is the predominant type of greenhouse gas emitted as a fugitive emission in the oil and gas sector, due to safety concerns helium is frequently the gas used in ISO leakage detection flow medium. The ISO test can be done with either methane or helium as the test fluid/ medium; whereas the API test only allows methane. In ISO there is no correlation intended between measurements of leak rate when the test fluid is helium and when the test fluid is methane.
  • As per the ISO standard, there are different methods for acquiring leakage rate data such as a Global method (helium only) e.g. vacuum and bagging and a Local method (helium/methane) e.g. sniffing. In the local method, a correlation is applied to the leakage measured by sniffing to estimate overall leakage from the valve stem as well as other body joints wherein global method actual leakage rate is measured without any estimation and it only applicable to valve stem leakage detection, not to other body joints leakage detection. In API standards leak measurements shall be sniffed using a detection probe only.
  • As per ISO standard, a Performance Class is defined by the combination of the tightness class, endurance class (mechanical cycles and thermal cycles) and temperature class.
  • In ISO standards; Tightness class applicable for stem (or shaft) has three different leakage limits which range from an extremely stringent (Class A) to a non-strict (Class C); When the test fluid is helium the tightness classes are identified as (Class AH ≤ 10-5, Class BH ≤ 10-4 and Class CH ≤ 10-2  leakage rate in mg/(s*m)) and when methane is identified as (Class AM ≤ 50ppm, Class BM ≤ 100ppm and Class CM ≤ 500ppm).

- As in API standards, there is no tightness class specified; the measured leakage throughout the test does not exceed 100 ppmv.

  • In ISO standards; Endurance classes for Isolating valves these are CO1 (205 cycles including 2 thermal cycles), CO2 (1500 cycles including 3 thermal cycles) and CO3 (2500cycles including 4 thermal cycles) and For Control valves these are CC1 (20000 cycles including 2 thermal cycles), CC2 (60000 cycles including 3 thermal cycles) and CC3 (100000cycles including 4 thermal cycles).

-As in API standards, API 624 Valves shall be subjected to a total of 310 mechanical cycles and 3 thermal cycles and In API 641 total of 610 mechanical cycles and 3 thermal cycles

  • In ISO standards; Temperature class testing can be performed at -196°C (-320°F), -46°C (-51°F), +200°C (392°F) and 400°C (752°F).
  • In ISO standard various class designations are chosen based on both the valve type and the intended application. If service application is stringent then stringent class i.e. Class A (for lethal gas) and CO3/CC3 (for frequent operation) is selected as required by the end-user/ requested by the purchaser or by recommendation of valve manufacturer wherein API the leakage limits and mechanical cycles are throughout the same for every service application.
  • No stem seal adjustments are allowed in the API standards. If at any point the leakage exceeds 100 ppmv, the test is considered a failure whereas in ISO standard if stem leakage has been measured in excess of the target tightness class selected i.e. Class A/B/C then mechanical adjustments of stem system during the type test shall be permitted only once in CO1 or CC1, two adjustments are accepted in CO2 or CC2 and three are in CO3 or CC3

Which Standard is most appropriate for your Valves?

  • 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.
  • Selection of these standards depends on end-user test requirements, it is based on the valve type and design feature, it is based on process application, it is based on the geographic market the valves are being sold into.

I tried to cover all the important points which are helpful for comparison between API and ISO standards. I hope you will like it. If there any part is missing then you can give your ideas.