Published: 08 February 2016 Written by Rich Davis
The API Standard Committee on Piping and Valves has published some standards on fugitive emissions. While other standards do address the issue of fugitive emissions, the API standards have also attempted to address leak rates and other aspects of valve performance.
The standards committee started with API 622 Type Testing of Process Valve Packing for Fugitive Emissions. This standard establishes requirements and parameters for the following tests:
Packing Material Composition and Properties
The fugitive emissions testing includes 1510 mechanical cycles with five thermal cycles—ambient to 500°F. The test methods apply to packing for use in on-off valve rising stem and rotating stem motions.
The latest standard was published in 2011 and currently is undergoing revision. A test chamber for 1/8-inch packing is being added as a number of tests on API 624 have indicated issues with the smaller packing cross-section.
API is also changing the leak test monitoring equipment by opening up the types of equipment allowed to detect fugitive emissions. An important note on this section: The review of the packing manufacturers testing should include an overview of all sections of the testing.
The expectation from the valve buyer some standards on fugitive emission still be an extended warranty and this means that the potential for oxidation and volume loss due to the heat loss of lower temperature materials may cause premature failure, so it is essential to look beyond the fugitive emissions numbers and review all of the results.
The committee hopes the new standard will permit up to 100 ppmv methane leak rate with no allowed adjustments, along with the above-referenced changes.
Following the development of the API 622, the API 624 Type Testing of Rising Stem Valves Equipped with Flexible Graphite Packing for Fugitive Emissions standard was developed and published in 2012.
The API 624 standard specifies the requirements and acceptance criteria (100 ppmv) for fugitive emission type testing of rising and rising-rotating stem valves equipped with packing previously tested in accordance with API Standard 622. The fugitive emissions testing includes 310 mechanical cycles with three thermal cycles—ambient to 500°F.
An optional low temperature test at -2°F (-29°C) may be performed if requested by the purchaser. The elevated test temperature is to be 500°F ± 5% (260°C ± 2%).
The test pressure must be the lower of 600 psig or the maximum allowable pressure at 500°F per ASME B16.34 for the applicable material group and shall be held constant throughout the test. The packing must also be suitable for use at service temperatures 20°F to 1000°F (–29°C to 538°C). Valves larger than NPS 24 or greater than class 1500 are not covered in the scope of the standard.
Both of these current standards identify requirements of requalification, i.e., if the manufacturing location changes or if the valve design changes.
API is currently working on developing a standard to cover quarter-turn type valves. It will be titled API 641 Quarter Turn Valve FE Test.
The standard specifies the requirements for type testing quarter-turn valves for fugitive emissions and applies to all stem seal materials. Conversations have been held about the types of mechanical and thermal cycles, and the committee has settled on 100 ppmv as the maximum allowable leakage.
The wide range of quarter-turn valves complicates the development of the standard. Also, the inclusion of all types of stem seals further complicates the test temperature and pressure requirements.
Finally, the Upstream & Midstream API 6D Valves group has decided to develop a separate standard covering their valves and are currently working with the Association of Wellhead Equipment Manufacturers to make that happen. The group is aiming for completion by the end of 2016.