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• Within one and half year of commissioning of VDU heater, its radiation section tubes (from bottom) excessive sagging / bowing happened. What is the main reason of tube sagging / bowing?

  Sep-2025

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Answers

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• Marcio Wagner da Silva, Petrobras, marciows@petrobras.com.br

  These phenomena are strictly related to non-uniform heating and thermal stress of the tubes. These symptoms can be related to coke deposition in the fired heater tubes as well as flame impingement, this is a serious issue once can lead to tube failures under operation causing fire and explosion, I understand that the equipment should be taken out of operation immediately. The question is not mentioned if the fired heater has skin points temperature (tubeskin thermocouples) which can easily reveal if the tubes are operating under high temperature which can be caused by flame impingement and coke deposition in the tubes. If they do not exist, it's possible to carry out a deep evaluation of the tube's temperature using infrared thermography. Another point to check, more related to the mechanical stress is the failure of tube support which can lead to mechanical stress scenarios not foreseen in the design leading to sagging and bowing of the tubes.

   

  Sep-2025