Valve Sealing Performance: Standards, Selection, and Low-Leakage Detection

In industrial production, piping systems transport a wide variety of media, including raw materials, finished products, energy, and waste. Valves play a crucial role in controlling flow, regulating pressure, and ensuring the safe and efficient operation of these systems. Every opening and closing of a valve determines the direction and volume of media flow, directly affecting the stability and efficiency of the production process.

However, a valve’s performance depends not only on its operational capability but also on its sealing performance, which is critical to preventing leaks and ensuring safety. This article explores the importance of valve sealing, standards for sealing grades, and methods for detecting low-leakage valves.

The Importance of Valve Sealing Performance

Valve sealing performance refers to a valve’s ability to prevent media leakage at key sealing points. Its significance cannot be overstated, as leakage can compromise efficiency, safety, and environmental protection. There are three primary sealing locations:

1. Valve Seat and Closure Member – the core sealing area. Leakage here, called internal leakage, affects the valve’s ability to cut off flow, disrupting production.

2. Packing and Valve Stem / Packing Box – leakage here is called external leakage, which is more serious as it allows media to escape outside the valve, causing economic loss, environmental pollution, and potential safety hazards.

3. Valve Body and Valve Cover Connection – another potential site for external leakage.

External leakage is particularly critical for hazardous media (flammable, explosive, toxic, or corrosive), as even small leaks can lead to accidents. For high-risk applications, zero external leakage is mandatory.

Selection of Valve Sealing Grades

Accurate assessment of sealing performance requires adherence to internationally recognized sealing grade standards.

1. European and International Standards

European and American standards have largely replaced the older Soviet classification system. Key examples include:

• EN 12266-1:2003 – aligned with ISO 5208:2008, excluding certain grades (AA, CC, EE).

• ISO 5208:2008 – expanded the previous 1999 version by adding six sealing grades (AA, CC, E, EE, F, G) for detailed classification.

• ISO 5208 also provides cross-references with API 598 and EN 12266, facilitating conversion between standards. Leakage rates are calculated based on valve size.

2. API 598: American Petroleum Institute Standard

• API 598 is widely used for pressure testing and inspection of valves including gate, globe, check, plug, ball, and butterfly valves.

• Certain historical inconsistencies exist between API 598 and API 600/ISO 5208. In engineering projects, it is essential to specify the version to avoid discrepancies.

3. API 6D: Pipeline Valve Requirements

• API 6D:2008 specifies acceptance criteria for valve leakage:

  • Soft-seated valves and oil-sealed plug valves: leakage ≤ ISO 5208 Grade A (no visible leakage).

  • Metal-seated valves: leakage ≤ ISO 5208 Grade D, or twice that for special cases.

• The standard emphasizes selecting leakage tests based on valve type, size, and pressure, balancing performance with production cost. Low-pressure tests are recommended for long pipelines, while high-pressure tests may reduce performance for elastic-sealed valves.

4. Control Valve Sealing (ANSI/FCI 70-2 / ASME B16.104)

• Selection between metal elastic sealing and metal sealing depends on media characteristics and operation frequency.

• Grades IV–VI are typically used for critical control valves, ensuring adequate performance. Grade selection should be specified in the purchase contract.

5. Test Water Chloride Content

• API 6D: chloride content ≤ 30 μg/g for austenitic stainless steel valves.

• ISO 5208 and API 598: chloride content ≤ 100 μg/g.

• The test water chloride concentration should be clearly stated in the contract to prevent inconsistencies.

Detection Standards for Low-Leakage Valves

With stricter environmental and safety requirements, low-leakage valves—valves with minimal external leakage—are increasingly demanded. Advanced detection methods include:

1. EPA Method 21 (USA) – focuses on volatile organic compound leaks.

2. ISO 15848 – evaluates tightness, durability, and temperature resistance. Tightness is graded A, B, or C. Leakage at the valve body must be ≤50 cm³/m³; stem leakage is calculated based on diameter.

3. SHELL MESC SPE 77/312 – similar to ISO 15848, with grading and type approval procedures for on-off and control valves. Bellows-sealed valves can achieve a tightness grade below ISO Grade A.

Conclusion

Valve sealing performance is a critical factor in industrial production. It affects efficiency, safety, economic outcomes, and environmental protection. Choosing the correct sealing grade requires consideration of standards, media type, operating conditions, and valve design. Low-leakage valves must be evaluated using rigorous detection methods to ensure optimal performance.

By adhering to internationally recognized standards and selecting appropriate grades, engineers can ensure valves operate reliably, reduce leakage risks, and safeguard industrial processes.

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