In industrial production, especially in the energy and chemical sectors, equipment sealing is of paramount importance. However, many pieces of equipment may experience some subtle chemical leaks during operation, a phenomenon known as fugitive emissions. Although these minor leaks may appear inconspicuous, they pose potential threats to the environment and human health. Therefore, understanding and controlling fugitive emissions, particularly valve leaks, has become an important issue that the industrial sector urgently needs to address.
Fugitive emissions refer to unintended or hard-to-detect chemical leaks from equipment in industrial facilities. In the energy and chemical industries, valves, storage tanks, flanges, and pumps are the main contributors to medium leakage. Among these, valves have attracted the most attention from users due to their large quantities and dispersed installation. These leaked chemicals, such as benzene, methane, and ethanol, volatile organic compounds (VOCs), can severely harm air quality and contribute to ozone formation. Therefore, government agencies have established clear restrictions on fugitive emissions, and companies that violate these regulations may face substantial fines.
In European and American countries, after nearly two decades of persistent efforts by local governments and enterprises, the use of low-emission valves has been widely promoted, and the proportion of valve-related leaks has gradually decreased. Today, in chemical plants in Europe and the U.S., odors are virtually undetectable. This achievement demonstrates that reducing the small fugitive emissions from valves to the external environment is a necessary measure for improving environmental pollution.
In typical industrial facilities, valves are the main source of uncontrolled VOC emissions. Studies show that valves are estimated to account for 62% of total uncontrolled VOC emissions. Therefore, installing low-emission (Low-E) valves has become an effective means to reduce fugitive emissions and is a solution widely adopted across the industry.
The emergence of low-emission valves brings multiple benefits to industrial production. First, they can significantly reduce the emission of harmful gases and lower environmental pollution. Second, using low-emission valves helps enterprises comply with strict environmental regulations, avoiding heavy fines for violations. Additionally, low-emission valves can improve production efficiency and safety, reducing material waste and equipment damage caused by leaks.
Testing and Certification of Low Fugitive Emission Valves
Because the amount of fugitive emissions is extremely small, conventional water or nitrogen tests cannot accurately determine leakage. Therefore, more scientific methods and precision instruments are required for detection. Currently, the industry primarily uses the “sniffer” method for quantitative detection of invisible leaks.
To ensure a valve's low-emission performance, there are several ways to classify a valve as a low-emission valve. Factories may accept valve manufacturers that meet any of the following conditions:
Provide a written guarantee that the valve's leakage rate will not exceed 0.01% within five years.
Provide a written guarantee, professional certification, or equivalent documentation proving that the valve has been tested according to recognized good engineering practice and that the leakage rate does not exceed 100 ppm.
However, relying solely on a manufacturer's written guarantee carries some uncertainty. If a valve does leak, plant operators should consider the consequences. Does the guarantee only cover replacing the leaking valve? Does it compensate for the costs related to valve replacement? These questions must be carefully considered when purchasing low-emission valves.
Fortunately, the American Petroleum Institute (API) and the International Organization for Standardization (ISO) provide industry tests to determine whether a valve should be classified as a “low-emission valve.” These testing methods include:
API 622: The 2nd edition of API 622 is an international performance testing standard for packing materials, considering factors such as temperature, pressure, thermal cycling, and mechanical cycling. The 2nd edition specifies 1,510 mechanical cycles and 5 thermal cycles. High-temperature tests should be conducted from room temperature to 260°C (500°F) and 0 to 600 psig (0–41 barg) pressure. The test medium is methane, with an allowable leakage of 100 ppm.
API 624: Covers rising-stem valves tested using methane as the test medium. Valves must perform 310 cycles and three thermal cycles (tested at ambient temperature, high temperature, and then ambient temperature again), with methane leakage below 0.01%. The 1st edition of API 624 is a type test for low-emission graphite-packed rising-stem valves. The standard covers valves with a maximum diameter of 24" and requires testing of both rising and rotary valve stems in original condition. The procedure requires 310 mechanical cycles and three thermal cycles at a maximum of 260°C (500°F). The allowable maximum leakage is 100 ppm. Tested valve packing must have passed API 622 tests, and the working temperature range is -29°C to +538°C (-20°F to 1000°F).
API 641: API 641 is one of three widely used valve standards for evaluating low-emission performance during accelerated life testing. Among these, API 641 is the most stringent for quarter-turn valves, covering different designs, temperature classes, and seal combinations. To pass, valves must undergo 610 cycles under extreme temperatures, complying with a strict maximum leakage of 100 ppmv.
ISO 15848-1: This testing program evaluates external leakage of valve stem seals (or shafts) and body joints of isolation and control valves. It involves injecting helium or methane through the valve and digitally measuring any escaped gas. Since it applies to both seals and joints, it is considered a “whole valve” test. It provides acceptable procedures for measuring, testing, and identifying fugitive emissions. However, because the test is not conducted under typical process conditions, results may be misleading.
Differences in Testing Methods and Considerations
API testing provides a simple pass or fail result—a valve either meets the low-emission classification or it does not. ISO testing, however, allows for various “grading” evaluations of valve performance. ISO grades can classify a valve as “low-emission” even if it does not meet the EPA requirement of ≤100 ppm leakage. For example, “Seal Class CM” describes a valve with methane leakage above 100 ppm but below 500 ppm.
Moreover, according to ISO, “when the test fluid is helium (AH, BH, CH classes) and when the test fluid is methane (AM, BM, CM classes), no expected correlation exists between leak-tightness classes.” This is partly because different test fluids yield different data. Testing with helium rather than methane results in leakage rates reported in atm-cm³/s proportional to stem diameter. Although this metric more accurately defines leakage than ppm, there is no method to convert atm-cm³/s to observed ppm, making interpretation difficult when using helium to assess compliance with the EPA ≤100 ppm standard.
Ideally, low-emission valve testing should be conducted in third-party laboratories rather than by the valve manufacturer. When manufacturers hire independent third parties, impartial organizations verify that valves meet test standard requirements. Plants should then obtain valve certificates from manufacturers, including documentation of third-party verification, test locations, and results.
The importance of third-party testing lies in its fairness and reliability. Independent laboratories provide objective results, avoiding biases due to manufacturer interests. Through third-party testing, plants can more accurately evaluate valve low-emission performance and make informed purchasing decisions.
In practice, selecting the appropriate low-emission valve according to specific operating conditions is critical. Some common application cases include:
For ambient temperature CL2 gas and phosgene, ISO 15848 Class A leakage is generally required. For globe valves, bellows + PTFE packing dynamic seals are used, with PTFE-wound gaskets and body-cover flanges in male-female configurations. This design effectively reduces leaks and meets stringent environmental requirements.
For ambient and high-temperature hydrogen, ISO 15848 Class B or API 624 100 ppm leakage standards are generally required. For gate valves, low-leakage graphite packing sets are selected, with gaskets in corrugated or wound structures. These material and structural choices ensure valve sealing under high-temperature and high-pressure conditions, minimizing hydrogen leakage.
When selecting low-emission valves, plants should consider the following:
Manufacturer Reputation and Guarantee: Choose a reputable manufacturer and request a written guarantee that the valve leakage rate will not exceed 0.01% within five years.
Third-Party Testing: Ideally, testing should be conducted by an independent laboratory rather than the manufacturer. Third-party results are more impartial and reliable.
Applicability of Test Standards: Ensure the valve's test standards match actual operating conditions. For example, for high-temperature hydrogen, select valves compliant with API 624 or ISO 15848 Class B standards.
Cost vs. Benefit: Although low-emission valves may be more expensive, reducing fugitive emissions minimizes environmental risks and potential fines, offering significant long-term economic benefits.
Low-emission valves play a vital role in reducing fugitive emissions in industrial facilities. By adopting scientific testing methods and adhering to strict industry standards, valve leakage rates can be effectively reduced, improving environmental quality. When selecting low-emission valves, plants should comprehensively consider manufacturer reputation, third-party test results, the applicability of test standards, and cost-benefit analysis. Only then can they ensure optimal valve performance under real operating conditions, providing strong support for environmental protection and safe production.