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We have cook formation inside the coils of VDU heater and the metal of this coils are suffering from a hardness, Which method is the optimum for decoking, steam air or pigging to avoid metal damage?
 
Answers
19/12/2015 A: RUPAM MUKHERJEE, ENGINEERS INDIA LIMITED, rupammukherjee86@gmail.com
Steam air decoking is only applicable when you have the decoking pot system in the downstream available. The other option is online spalling although the heater must be designed to suit the spalled effluent temperature, typically exceeding 650 degC. One pass done at a time.
Pigging is a viable option but will require shutdown of the heater. Also, u must have spool pieces at inlet and outlet where the pig can be launched. Saying all this, the root cause for coking should be investigated to avoid similar occurances.
12/12/2015 A: Eric Vetters, ProCorr Consulting Services, ewvetters@yahoo.com
I would just add to the previous comment that pigging can sometimes be challenging in a vacuum furnace because of the number of different tube diameters found in most furnaces.
28/10/2015 A: Bruce Carr, Suncor Inc, matukaze1@hotmail.com
If you are having a problem with hardness I would prefer pigging especialy if the tubes have removable U return bends. Just make sure the company that you use is using soft bristle pigs to prevent gouging the interior of the tubes. Also ensure there are no stab in thermocouples anywhere in the system.