A fugitive emission test is a procedure of testing harmful gases or gaseous vapors in an industrial zone due to leaks or accidents. Fugitive emission test procedure is performed using helium (He) or methane (CH4) gas based on the method. The term “Fugitive” is used widely because these emissions are not considered and calculated during the design of the equipment and its components.
It is recommended to conduct a Fugitive emission test before the installation of valves and at regular intervals to avoid leakage of hazardous gas or vapour into the environment. It can also be done in case of any incident near valves to make sure everything is fine.
As per American Petroleum Institute (API), Low fugitive emission or low leaking means either no or very minimal (100 ppm till 5 years) leakage from the valve. Please note that EPA Has not defined any standards for Low Fugitive Emissions.
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There are 4 major types of fugitive emissions test methods:
In Fugitive Emission test method helium is used as the testing medium to measure the overall leak rate from the stem seal using a helium mass spectrometer. In this procedure, the leak source is enclosed in a tight vacuum container, which is evacuated and then connected to a helium mass spectrometer.
In Fugitive emission test procedure, pressurized Helium or Methane is used to measure the total leak rate of the stem sealing system. The leak source is enclosed by a flush chamber, a flush gas is passed through that chamber and it is allowed to be mixed with the leaking fluid from the stem packing. Then this mixture is passed through exhaust line and based on the concentration of leak fluid and flush gas leakage volume is calculated in ppmv unit
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This is the revised version of the Flushing method and in this method, only Helium is used to measure the total leak rate using Helium Mass Spectrometer. The leak source is enclosed by a bag volume i.e. air is passed through the bag and then is mixed with leak fluid from the stem packing. This mixture is analyzed by Helium mass spectrometer through a constant flow rate detector probe or sniffer.
In Fugitive Emission test procedure, Helium as fluid is used to measure Helium concentration due to emission from stem sealing and body sealing using a detector probe or sniffer. In the case of Methane as a testing fluid, the process remains the same but instead of a Helium leak detector, VOC Detector is used.
Various organizations have came up with Fugitive Emissions Testing Standards such as API, EPA, ISO, MESC, ANSI, etc. to assess the performance of valve packing and valve emissions. There has been many discussions on various forums about comparison of standards from all agencies.
Amongst all Agencies, Fugitive Emission Testing Standards from API and ISO are widely used. ISO 15848 is very popular as it describes measurement, test and qualification procedures for fugitive emissions at industrial valves.
ISO 15848-1 is a classification system and a qualification procedures for type Fugitive Emissions testing of valves. ISO 15848-2 specifies production acceptance test of valves for valve manufacturer.
Below is the comparison of various prescribed fugitive emissions testing standards as per ISO and API:
| Comparison Factor | ISO 15848-1 | ISO 15848-2 | API 622 | API 624 | API 641 |
| Current Revision: | 1st 2006-01-15 | 1st: 2006-08-15 | Oct. 2nd, 2011 | In process of 1st publication | `Oct. 2016 |
| Qualifies: | Valve Design | Production | Packing | Valve Design | Valve design |
| Testing type/ Production acceptance | Type Testing | Production Accpetance | Type testing | Type testing | Type testing |
| EPA Method 21 compliant: | Yes | Yes | Yes | Yes | yes |
| Pre-Requisite: | None | ISO 15848-1 qualified valve design | None | API 622 qualified packing | API 622 qulified packing |
| Test Medium: | Helium or Methane | Helium | Methane | Methane | methane |
| Packing Tested in: | Valve | Valve | Fixture | Valve | Valve |
| Test Pressure: | Rated Valve Pressure at Test Temperature per ASME B16.34 | 6 bar (87 psi) | 0-600 psi | The lower of 600 psi or maximum allowable pressure at 500°F (260°C) per B16.34 | As per Valve group A, B, C, D, E |
| Test Temperature: | As pertemperature chart table -196°C, -46°C, Room temp. , 200°C and 400°C | Ambient | Ambient and 500°F (260°C) | Ambient and 500°F (260°C) | As per Valve group A, B, C, D, E |
| Mechanical Cycles: | For Isolating Valve: CO: 205 CO2: 1500 CO3 : 2500 For Control Valve CC1: 20,000 CO2: 60,000 CO3: 10,000 | 5 | 1,510 | 310 | 610 |
| Thermal Cycles: | Variable[1] | 0 | 5 | 3 | 3 |
| Leakage measurement Method | Vaccum, Flushing, Bagging, Sniffing, | Sniffing | N/A | sniffing | Sniffing |
| Allowable Packing Adjustments: | 1 (during testing only) | 0 | Packing adjustment allowed if leakage exceed 500 ppm | 0 | 0 |
| Measured Units: | mg/sec-m | ppm | ppm | ppm | ppmv |
| Acceptance Criteria: | As per tightness class: For stem seal: fluid helium Class AH: 10-5 mg/s-m Class BH: 10-4 mg/s-m Class CH: 10-2 mg/s-m For Stem seal: Fluid- Methane Class AM: 50 ppmv Class BM: 100 ppmv Class CM: 600 ppmv From body joint seal: 50 ppmv | For Stem seal: Fluid- Methane Class A: 50 ppmv Class B: 100 ppmv Class C: 600 ppmv From body joint seal: 50 ppmv | 500 ppm | 100 ppm | 100 ppm |
| Qualification Coverage: | Same basic design Stem Diameters: 50% lower and 200% higher. Pressure class: Same class and lower[4]. | N/A, Because each and every valve need to be tested | Packing Only | – | 1. Te, Pe, Pa valves are less than or equal to the valves specified in perticular applicable group 2. Stem diameters are from half to twice the tested valve diameter 3. height of stem seal is between 75% to 125% of existing tested valve |
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