How do you prevent coking in fired heater tubes for hydrocarbon service?

Coking mechanisms: thermal cracking (excessive tube metal temperature), catalytic coking (metal surface catalysis), and condensation coking (heavy molecule deposition). Prevention: maintain adequate velocity (minimum 1-2 m/s liquid), avoid hot spots (proper burner adjustment, even heat flux distribution), keep tube metal temperature below coking threshold (material upgrade for higher limits), inject steam or dilution (reduces hydrocarbon partial pressure), use specialized metallurgy (low catalytic activity alloys like aluminum-diffused tubes), and implement decoking procedures (steam-air, pigging).