Many industries are interested in reducing fugitive emissions. Several standards and end user efforts work toward this goal:
- International Organization for Standardization (ISO) 15848 Measurement, test and qualification procedures for fugitive emissions
- Part I – Classification system and qualification procedures for testing of valve types
- Part II – Production acceptance test of valves
- American Petroleum Institute (API) 622 Type Testing of Process Valve Packing for Fugitive Emissions
- API 624 Type Testing of Rising Stem Valves Equipped with Graphite Packing for Fugitive Emissions
- End user defined fugitive emission reduction requirements
Because valve emissions are a major concern in the U.S., API created a document called “API 624 Type Testing of Rising Stem Valves Equipped with Graphite Packing for Fugitive Emissions.” The API 624 Task Force worked for more than two years to incorporate members’ views and regulator and manufacturer requirements.
The standard applies to rising and rising-rotating stem valves—including gate and globe valves—up to 24 inches in diameter.
The standard does not apply to class 1500# valves, because methane gas volumes could be difficult to handle during testing.
The test medium is methane. ISO has a similar test often used in Europe that uses helium as a test medium. Because methane is easily available in North America and the gases have similar properties, manufacturers and the committee preferred methane to helium.
In total, 310 test cycles are required, three of which are thermal cycles. The test includes 50 low-temperature cycles followed by 50 high-temperature cycles, totaling 300 cycles. An additional 10 cycles are added based on user preference.
The temperature application range is from -29 to 538 C. The last 10 cycles are user defined and can be as low as -45 C. Because the test method determines the integrity of leakage requirements, this was adapted as the standard temperature for testing.
Gland bolts may not be tightened during testing. Once the valve is on the test bench, no further modifications are allowed.
The valve stem test orientation is vertical. Because gate and globe valves are large and heavy, the vertical orientation allows users to obtain the best test results. To comply with API 624, several valves must be tested. Similar industry principles applied to test valves qualify valves that are two nominal sizes smaller, one size larger and one pressure class lower.
Allowable leakage is 100 parts per million. This standard was chosen based on Environmental Protection Agency (EPA) regulations.
Gate and globe valves must be tested separately. Gate valves, for example, need four tests under API 602, eight tests under API 600 (for valves up to 20 inches in diameter) and eight tests under API 603. Globe valves need four separate tests under API 602.
Test valves should be production valves not specially manufactured test valves. This was required to determine that valves manufactured by standard production meet and exceed the test requirement/s.
Since API 624 was released, testing companies have been preparing for an increase in the number and size of test valves. New test houses are also coming online.
Leak screening should be completed on accessible components using a portable organic vapor analyzer in accordance with EPA Method 21 or by using alternate methods that provide an equivalent result. In some cases, Method 21 has been considered too slow and labor intensive, especially in small facilities. For these reasons, other methods may be used.
The industry should carefully monitor the implementation of API 624. Users should validate claims from valve manufacturers by requesting to view test results. Reputable test shops have noted:
- The number of cycles on some valves could damage packing, because some smaller valves do not include grease ports to keep the stem consistently lubricated.
- Failures of valve stem threads, yokes and glands can occur during testing.
- Grease is sometimes trapped in the packing, causing leakage.
- A few greases create volatile organic compounds and burn-off at higher temperatures.
- Testing in vertical orientation generates more heat in the yoke area.
An experienced testing company can provide guidelines to manufacturers about use of packing, valves, greases and testing requirements. Table 1 shows the results of an anonymous survey of end users concerning their adoption of API 624.