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.

Every radiant tube is designed against a rupture life, not a wall-loss allowance. Creep is what spends it, quietly, whether or not the thickness gauge notices. Why it matters Every fired heater radiant tube is sized against two numbers at once: an internal-pressure hoop-stress requirement, and a creep-rupture life at its design metal temperature, per API Standard 530. The pressure calculation gets checked at every turnaround with a thickness gauge. The creep calculation gets

Coke does not just foul the tube. Left too long, it carburises the metal underneath. At a glance The problem Carbon diffuses into P22, P5 and P9 tube steel above 593°C (1100°F), making it hard and brittle without reducing wall thickness. Why it's missed A thickness gauge cannot see it. A tube can hold 90% of its original wall and still be days from a brittle fracture. What causes it Decoking itself, and raising firing rate to compensate for a coked-up coil — both operator dec