Aging Convection Section Life Assessment

This paper presents a case study of a remaining life assessment for several coils in a convection section of an ethylene steam-cracking furnace. KnightHawk Engineering, Inc. (KHE) performed this assessment for a client with a steam-cracking furnace that was originally commissioned in the early 1990s and was nearing the end of a prior 20-year remaining tube life prediction.

The life assessment was conducted using methods and acceptance criteria from API-579 Fitness-for-Service. Analyses performed on the convection section tubes evaluated (i) wall thinning by oxidation corrosion and plastic collapse, (ii) creep damage accumulation and creep rupture, (iii) fatigue and creep-fatigue interaction due to cyclical operation, and (iv) deflection by static loads and accumulated creep strain. The tubesheet supports were evaluated for (i) wall thinning by oxidation corrosion and plastic collapse and (ii) creep damage accumulation and creep rupture. Tube fins were evaluated for oxidation corrosion.

Based on the results of the analyses performed, KHE calculated the remaining life of the convection section and identified potential necessary replacements to ensure a reliable operation for the next 100,000 hours of service. Recommendations for future inspection and monitoring plans as well as potential modifications were also provided based on the remaining life assessment.