Process-side hydrocarbons, leak

The process-side hydrocarbons leak into the cooling water return line. 

A tube with a silver streak will begin to bulge at its hottest point. Eventually, the tube wall will thin out over the bulge and split open. Figure 15-10 illustrates this problem. Process-side hydrocarbons will spill into the firebox and ignite. Depending on the size of the leak and how quickly the operators shut the unit down, the heater may or may not burn down. 

If a heat exchanger has process fluid on one side and lower pressure cooling water on the other a tube leak will cause hydrocarbons or toxic chemicals to enter the cooling tower. This can lead to a fire at the tower or the widespread dispersion of the toxic materials. 

---