The 3°C Rule
NACE/SSPC and most client specifications (Aramco SAES-H-001, ADNOC AGES-C-04) require the steel surface temperature to be at least 3°C above the dew point before abrasive blasting or paint application. If the difference is less than 3°C, work must stop until conditions improve.
Measurement Best Practices
Use a whirling hygrometer (sling psychrometer) or digital psychrometer for accurate RH readings. Measure steel surface temperature with a contact thermometer. Check conditions every 2-4 hours and whenever weather changes. Document all readings in the daily coating log.