The document discusses a creep damage assessment of the Reactor F105 vessel in a catalytic reforming unit. It provides background on the unit's commissioning in 1971 and history of reported damage since 1999. A stress analysis using FEA found stresses were approximately 50MPa compared to 68MPa using a flat plate solution. While rupture life is predicted to be consumed, remaining creep life depends on the integrity of the remaining wall after grinding. Based on available data, remaining life is estimated to be 50% with an inspection interval of 2 years recommended to understand long term degradation.

1. CATALYTIC REFORMER UNIT
(REACTOR FFS ASSESSMENT)
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by Amin Muhammed
PTE-EMMI
2/9/2011 1
Shell Projects & Technology

2. CATALYTIC REFORMING UNIT
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3. HISTORY
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4. HISTORY
Reactor vessel F-105 was commissioned in 1971, construction material
is 1.25 Cr 0.5 Mo material to BS -1515:1965 code
First reported damage goes back to 1999, at that time the damage had
been ground out and unit was put back in service.
In 2009 crack like damage was reported; but not contributed to creep
damage, damage had been ground out.
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damage, damage had been ground out.
In April 2009, additional damage had been found close to original
damage. An creep assessment was conducted on the reported damage
in Reactor F105 top/bottom nozzle welds.
Consumed life to date 326,446 hours. Current operational cycle 6
years. Next TAR 9/2009; first replacement opportunity for reactors
2015
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5. REACTOR F105 – SCOPE
2009 Reported Damage/repair situation
Top Nozzle head - plate inclusions/fabrications defects, no evidence
of active service-related propagation; ground out to 12mm depth
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Bottom nozzle - gas porosity/welding related hydrogen cracking;
nozzle weld repair/service related creep damage. Excavated,
profiled and left in place on the basis of previous life assessment
[note: low (2 yrs min) initial remaining life estimate]
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6. REACTOR F105 – SCOPE
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7. REACTOR F105 – SCOPE
Establish level of prior damage (see NDT, replication results etc)
Derive appropriate stresses from FE analysis compare with classic flat
plate solutions
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Provide life assessment
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8. REACTOR F105 – STRESS ANALYSIS
FEA analysis performed to establish limit load and stress distributions
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9. REACTOR F105 – STRESS ANALYSIS
Reference stress based on FEA results rather than flat plate solution
resulted in a ref. stress of ∼50MPa approx compared to 68 MPa with flat
plate solution
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10. REACTOR F105 – TEMPERATURE
Operational temperature data available from 1998 onwards
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11. REACTOR F105 – REMNANT LIFE?
Predicted rupture life using R5
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Rupture life has been consumed at this point.
Future damage is likely to develop slowly and progressively.
Creep data scatter and unknown material properties make remnant life
predictions for safe operation difficult.
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12. REACTOR F105 – REMNANT LIFE?
Replica’s required to indicate as repaired condition
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13. REACTOR F105 – REMNANT LIFE?
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14. REACTOR F105 – REPLICA POST REPAIR
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Replica result after defect removal suggests very little creep damage in
base metal, but need confirmation from weld metal and HAZ
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15. F105 –SUMMARY/CONCLUSION
Vessel life assessment of the basis of stress analysis and creep rupture
data alone is inconclusive, as a result of the variability in the available
data;
Lower bound remaining life estimates indicate that locally creep life is
exhausted and this is consistent with inspection findings to date.
Remaining creep life will depend on the condition and integrity of the
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Remaining creep life will depend on the condition and integrity of the
remaining wall, post grinding.
Inspection on the basis of replications shows no creep cavities to date,
however service conditions inherently imply that the creep life is at least
partially consumed.
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16. F105 –SUMMARY/CONCLUSION
A best estimate, on the basis of available data would suggest that life
consumption is probably in the region of 50%. Based upon experience
of life estimation on the basis of replica investigations, a prudent initial
inspection interval would appear to be 2 years from the date of the last
inspection.
Care should be taken in planning and scheduling future inspections to
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Care should be taken in planning and scheduling future inspections to
ensure sufficient time is available for vessel replacement in the event that
future degradation occurs at a faster rate than presently anticipated.
This fact has also been considered in arriving at the recommended
inspection interval such that at least two future inspection opportunities
are likely to be available as the basis for understanding long term vessel
degradation.
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