Usually, cleaning actions should be

Usually, cleaning actions should be taken when the temperature rise reaches 30°C above the basic value measured during start-up. 9.2Decolorated tube coils A spotwise decolorated coil surface indicates poor aligment of the flame. Irregular decoloration of single coil passes indicates unequal flow of heat transfer fluid. 10.Heater bottom Check condition of refractory lining (7). Due to thermal stress fissures will appear, which, as long as they are not wider than 10 mm, do not influence the life-time of the lining. Bigger fissures must be repaired. 10.1 Center insert (2) Check sheet steel shell for deformation and fissures Check condition of refractory lining (8). Due to thermal stress fissures will appear, which, as long as they are not wider than 10 mm, do not influence the life-time of the lining. Bigger fissures must be repaired. A defective sight glass (5) must be replaced.