Under what condition may hot oil coke in the heater tubes?

Hot oil can coke in the heater tubes primarily when the temperature of the oil exceeds 350°C (662°F). At this elevated temperature, the thermal decomposition of oil compounds begins to accelerate, leading to the formation of carbonaceous deposits, commonly referred to as coke. This process is a result of excessive heat breaking down the molecules of the oil into simpler structures that can then polymerize or oxidize, forming solid residues.

Maintaining operational temperatures below this threshold is crucial to prevent coking and ensure the heater's efficiency and reliability.

While other factors such as pressure, contamination, and flow rate can influence heater performance and oil quality, the critical aspect related to coking is the high temperature. Contaminated oil may also lead to coking, but the direct cause remains the temperature exceeding the specified limit. Inadequate pressure or excessive flow rates might alter the heating dynamics but do not reach the level of immediate coking risk presented by high temperatures.