Dew Point Calculator for Steel Surface Painting (3°C Above Dew Point)
Formula
DP = (a × T) / (b - T) + ln(RH/100) simplified to Magnus formula
Governing Standard
ISO 8502-4, SSPC-SP 1
Required Inputs
- Air temperature (°C)
- Relative humidity (%)
- Required margin above dew point (°C)
Output
Dew point temperature (°C) and minimum surface temperature for painting (°C)
Notes
Painting must occur when the steel surface temperature is at least 3°C above the dew point. At 30°C air temp and 70% RH, the dew point is 23.6°C — the steel surface must be at least 26.6°C before painting.
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