Probabilistic life assessment of fired heater tubes

Refinery furnaces

Component:

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

Objective:

  • A life assessment to underwrite five years additional service

Approach:

  • 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

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

Benefits:

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

Publication:

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