Fugitive emissions are unintended leaks of process gas or vapour to atmosphere through valve stem packing, bonnet joints and body seals — individually small, collectively the largest source of VOC and methane leakage in process plants. Valve tightness is certified by type tests such as ISO 15848-1, API 622 and API 624.
A valve does not need to fail to emit — every stem stroke drags a molecular film of process fluid past the packing, and thermal cycling relaxes bolted joints a little more each year. Studies consistently attribute around 60% of refinery fugitive VOC losses to valves, which is why regulators (EPA Method 21 monitoring, EU IED permits) and operators now write low-emission requirements directly into valve purchase specifications.
Three test standards dominate. ISO 15848-1 classifies whole valves by measured leak rate (tightness classes AH/BH/CH for helium, AM/BM/CM for methane) over defined mechanical and thermal cycles. API 622 qualifies the packing material itself, and API 624 (rising-stem valves) / API 641 (quarter-turn) burn-in those packings on production-representative valves with a 100 ppmv methane ceiling. A compliant datasheet cites the standard, class and cycle count — "low-E packing" alone is marketing.
Engineering options escalate from live-loaded graphite packing sets to full hermetic isolation with a welded bellows seal. VTXFLOW supplies live-loaded graphite packing sets and bellows-sealed gate and globe valves for low-emission duty. Where a project calls up a specific fugitive-emissions qualification — API 622 for the packing material, API 624 or ISO 15848 for the valve assembly — state it at enquiry so the packing and stem arrangement can be selected accordingly.