Monitoring for Hot Spots
We use visual checks, thermocouples on tube skins and IR thermography to monitor for hot spots.
Thermocouples have some limitations. They are placed where the designer anticipates the tubes will run the hottest; e.g., we expect to see one on the outlet tube of each pass. But if the hot spot occurs somewhere else, the tube skin thermocouple can’t tell us about it. A typical shutdown task is to place additional tube skin thermocouples where observed hot spots, repaired tube bulges or rupture locations suggest that they would be useful to augment the operator’s visual checks. Section 613 discusses the recommended type of tube- skin thermocouples and its installation. Selection of thermocouple locations is covered in Section 2126.
IR thermography can be a useful tool for temperature surveys inside fireboxes. While it can’t always give accurate tube skin temperatures, resolution is sufficient to provide a clear picture of hot spots that may be invisible or overlooked in routine visual checks. We also use IR thermography to monitor coke formation as reflected by increased temperature at locations where coke deposits occur inside the tube and also during steam-air decoking operations. See Section 614 for more details on IR thermography.