How many coker heater TIs are adequate to monitor coking/hotspots in the radiant tubes?  During the course of the run, we lose TIs over time and are currently trying to decide how many TIs are needed to consider this a valid barrier to protect against tube rupture from hotspots.  We’re also trying to determine the appropriate frequency for heater thermography as a mitigation.  Has anyone else experienced heater TIs going bad and found a solution?  If it matters, we have a FW double fired heater.
 
Thanks!