In This Article
- 1.ISO 15848-1 Emission Classes
- 2.API 641 — Fugitive Emissions for Quarter-Turn Valves
- 3.Low-Emission Packing Design
- 4.LDAR — Leak Detection and Repair
Fugitive emissions from valve stem packing are a regulated pollutant under EPA NSPS Subpart VVa (USA), EU Industrial Emissions Directive (IED), and increasingly under national regulations worldwide. Methane emissions from valve stems in oil and gas are a major Scope 1 GHG source — the IEA estimates that 30% of all methane emissions from oil and gas come from equipment leaks including valves.
ISO 15848-1 Emission Classes
| Class | Leak Rate (He equivalent) | Application |
|---|---|---|
| Class A | < 10 mg/s·m (< 10 ppm) | Highest sealing — toxic fluids, BTEX, H₂S |
| Class B | < 100 mg/s·m | General process — volatile organics, hydrocarbons |
| Class C | < 1,000 mg/s·m | Minimum requirement — standard service |
ISO 15848-1 testing involves pressurising the valve with helium and measuring leakage at the packing over 300+ open/close cycles (endurance test) and at high and low temperatures. Class A is the most stringent and is required for toxic services (benzene, H₂S, HF) and increasingly for all hydrocarbon service on new projects per IFC Performance Standard 3.
API 641 — Fugitive Emissions for Quarter-Turn Valves
API 641 (Qualification Testing of Quarter-Turn Valves for Fugitive Emissions) is the equivalent of ISO 15848-1 for ball, butterfly, and plug valves. It uses methane as the test gas (more representative of real service than helium used in ISO 15848-1). API 641 is specified by many US refiners and is a common requirement in ESHIA (Environmental and Social Impact Assessments) for new hydrocarbon projects.
Low-Emission Packing Design
- Multi-ring braided graphite packing with anti-extrusion rings — expanded graphite conforms to stem irregularities; provides ISO 15848-1 Class B sealing
- Live-loading (Belleville disc springs on gland follower) — maintains constant packing compression as graphite consolidates; extends re-packing interval from 2–3 years to 5–10 years
- PTFE chevron packing sets — for ISO 15848-1 Class A toxic service; lower friction than graphite; suited for automated valves where stem friction must be minimised for accurate positioning
- Dual stem seal (primary packing + secondary fugitive emission seal) — buffer cavity between the two seals is monitored for leakage detection
- Rising stem seal vs. rotating stem seal — rising stems have lower leakage probability than quarter-turn valves because the packing contacts a smooth stem surface linearly rather than rotationally
LDAR — Leak Detection and Repair
LDAR (Leak Detection and Repair) programmes require periodic inspection of process equipment including valves using optical gas imaging (OGI) cameras or EPA Method 21 (flame ionisation detector survey). Facilities with LDAR programmes benefit from specifying ISO 15848-1 Class B or better valves on all rotating equipment connections — it reduces the frequency and severity of LDAR findings, lowering compliance cost.
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