The cleaning cycle that is meant to extend tube life can just as easily end it. AT A GLANCE The problem A steam-air decoke hot spot pushes local tube-wall temperature past 593°C (1100°F) while the coke layer supplies exactly the carbon activity carburisation needs. The cleaning cycle becomes the damage event. Why it's missed Coil outlet temperature is an average. A single-fired heater's uneven burn hides a hot pass at precisely the resolution a routine decoke log cannot see.