Probabilistic life assessment of fired heater tubes

Refinery furnaces


  • Fired heater tubes, fabricated from 1¼CrMo steel, with over 200,000h service


  • A life assessment to underwrite five years additional service


  • A phased assessment, commencing with a lower-bound deterministic calculation progressing to a probabilistic life assessment, using standard materials data and post-exposure test results
Predicted failure probabilities based on standard materials data and on PET results


  • A conservative, code-based calculation generated life estimates considerably below the service actually achieved to date
  • A probabilistic calculation using standard materials properties, with a realistic distribution of rupture strength did not allow sufficient confidence to ensure secure long-term operation
  • Refining the probabilistic assessment by obtaining and using post-exposure stress rupture data from tube samples generated a remaining life estimate of over 50,000h at a 1% probability level


  • Confidence in the remaining life of the tubes, under a specified inspection and replacement plan


Brear, J.M., Williamson, J. and Cane, B.J.
“Life extension of high temperature process equipment”
NACE Int Conf ‘Corrosion 90’, Las Vegas, April 1990 Paper 196
Published in Materials Performance, November 1990, pp 70-75

Plant Integrity