November 11, 2015 at 5:46 am #19207
Paul R OrlowskiKeymaster
Furnace tube degradation occurs primarily due to corrosion, metallurgical changes and creep.
Furnace tube failures occur primarily due to creep. Creep is the time-dependent deformation occurring when tube metallurgy is subjected to stress (internal pressure) at elevated temperatures.
Unscheduled coker outages due to furnace tube failures are costly within the unit as well as throughout the refinery. This is because the entire refinery can be impacted due to reduced crude processing rates or adjustments to crude blends if the coker must be shut down or operated at reduced capacity.
Fortunately, creep can be simulated and the simulation used to predict what will occur in the future –the remaining life of a furnace tube.
Periodic infrared (IR) scans are being used more often to help monitor tube metal temperatures and check for hot tubes and hot spots.
Periodic IR scans ensure that the tubes monitored are representative of furnace conditions.
April 19, 2016 at 6:57 am #21322
As you mentioned correctly, Creep is one of the contributor to Furnace tube failure. But many other operating causes like flame impingement, burner tip choking, wrong draft profile from radiation floor to convection outlet, delay in furnace tube decoking/pigging, abnormal skin temperature rise, proportion of Fuel oil in the Total fuel fired etc. are significant contributors particularly with time.
April 19, 2016 at 1:19 pm #21324
Bsudhakar – are you still operating a fuel oil fired coker heater? There are not many that I have encountered these days?
High heat values and burner/draft issues make hot spots more likely with these types of heaters. All of the causes you mention can lead to hot spots and accelerated creep rates. If you don’t have a TMT there or have good visibility with IR camera, you might never know there was hot spot there. We always advocated for more TMT’s and better peep doors for just this reason.
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