- 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
- 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