Life assessment of visbreaker tubes

Visbreaker furnace,under construction


  • Serpentine coils in a cylindrical viscosity-breaker furnace, fabricated from 9CrMo steel


  • Residue oils are admitted to the viscosity breaker for thermal cracking
  • This process leads to a gradient of temperature, carburisation and fireside corrosion along the coil, with consequent variation in failure probability


  • To determine the variation of remaining life across the coil
  • To develop the optimum plan for tube replacements


Tube failure probability variation with position in coil


  • Remaining life of individual tubes, at various probability levels, determined as a function of position in the coil.
  • Tubes 15-19 predicted to have reached a critical probability level.


  • Accurate prediction of remaining life, as a function of position in the coil, verifiable against progressive inspection data
  • Optimum, risk-based, tube replacement plan

Plant Integrity