Flamepath Inspection — Ex d Equipment Guide
The flamepath is the precisely controlled gap between the mating surfaces of an Ex d flameproof enclosure. Its purpose is to cool any gases escaping from an internal explosion below the ignition temperature of the surrounding atmosphere. Flamepath condition is the most critical inspection item for Ex d equipment.
What to Check on the Flamepath
- Paint or coatings — paint on the flamepath surface reduces the effective gap or alters the surface characteristics. Category A if gap is maintained, Category X if gap is compromised.
- Corrosion — surface rust or pitting can alter the gap profile. Assess severity — light surface rust may be Category B, heavy pitting affecting the gap surface is Category A or X.
- Physical damage — burrs, scratches, or impacts can close or open the flamepath gap. Any damage affecting the gap is Category A or X depending on severity.
- Gap measurement — during Detailed Inspection, measure the actual gap with feeler gauges at multiple points around the flamepath and compare to IEC 60079-1 Table 1 limits for the gas group and volume.
Paint on a flamepath is one of the most common inspection questions in CompEx assessments. The classification depends on whether the paint has reduced the gap below the IEC 60079-1 limit. If the gap is still within limits — Category A (clean at next maintenance). If the gap is compromised — Category X (take out of service immediately).
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