Caltex Rbi

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RBI implementation

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Caltex Rbi

  1. 1. Case Study: RBI and its Application to Inspection of DHTU Flare Knockout Drums
  2. 2. AS3788 Pressure equipment – In-service inspection n Mandatory under NSW Occupational Health & Safety Regulation 2001 n Mandates maximum periods between internal inspections (Table 4.1) eg.
  3. 3. Notional risk increase with extended inspection date 100 Risk @ 2008 Risk @ 2006 High Acceptable Risk Level (ALARP) 75 Medium-High Risk Ranking 50 Medium 25 Low 0 1C-1 1C-2 1D-1 1D-2 1D-3 1D-4 1D-5 1D-6 1D-7 1D-8
  4. 4. Statutory inspection v. Risk based inspection 100 Relative Risk Statutory Inspection Level Optimum (Risk Based) Inspection Level 75 Relative Risk 50 25 0 1C-1 1C-2 1D-1 1D-2 1D-3 1D-4 1D-5 1D-6 1D-7 1D-8
  5. 5. Statutory inspection v. Risk based inspection n AS3788 advocates regular visual inspection, which may not adequately address all deterioration modes. It does not quantify the value of inspection techniques for mitigating risks other than thickness loss. eg. for Inspection Periods & Remaining Life Assessment, AS3788 is quantitative with regard to “Wastage” (para. 4.4.4.4, Appendix N), but qualitative with regard to environmental cracking & other deterioration modes (Appendix O concerns Fitness for Service, not Remaining Life) n API581 quantifies most available inspection techniques in terms of their effectiveness at reducing a range of deterioration modes
  6. 6. Risk Based Inspection “RBI may … be validly used … to modify some of [the AS3788] prescriptive requirements…” (AS3788 App.B)
  7. 7. What is Risk Based Inspection (RBI)? n “A way to extend runlengths/save maintenance $$$” n A method of using equipment history and the likely consequences of equipment failure to determine Inspection regimes focused on actual risks, so as to prevent unsafe incidents occurring n The RBI method is based on the API 581 base resource document – 23 major oil & petrochemical companies – massive statistical analysis of petrochem facilities over a number of years – “complex and … best suited for use in a computerized form” n Each piece of equipment is assigned a risk ranking based on the Probability and Consequence of a failure (loss of containment)
  8. 8. RBI principles – API 581 n Consequence (loss of containment) n Flammability Not influenced by inspection! n Toxicity n Production loss n Probability – deterioration modes n Internal corrosion n External corrosion Can reduce by effective inspection n Environmental cracking (eg. stress corrosion, hydrogen induced)
  9. 9. Typical risk matrix
  10. 10. Uninspectable risk n Cannot reduce risk to zero! – Human error – Natural disasters – External events (eg. falling objects) – Secondary effects from other nearby failures – Deliberate acts, sabotage – Fundamental limitations of inspection methods – Design errors – Previously unknown mechanisms of deterioration
  11. 11. Can inspection extend the life of an asset? n Can’tinspect good condition back into equipment at end of life! (API581 9.3.3.3d) n However…we don’t arbitrarily retire equipment at the end of its design life n Inspection and recertification are crucial to maximising the service life of equipment
  12. 12. 45C-612 & 45C-612A – inspection history n C-612 n C-612A – in service Oct 1978 – Feb 1980: visual – Feb 1980: visual – Aug 1982: visual – May 1983: visual – Jun 1985: visual – Sep 1987: visual (internally – Jan 1989: visual (internally coated) coated) – Sep 1991: visual – Jan 1992: visual, MPI – Sep 1995: visual – Apr 1996: visual, MPI – Feb 2002: visual 45C-612A is the vessel due for inspection based on time
  13. 13. 45C-612A – history of incidents H2S release on attempting to open for inspection n Mar 2002 n Sep 2003 Inspection requested to assess possibility of extending run via external inspection techniques
  14. 14. 45C-612 & 45C-612A – base data n Process: flare gas – water + ~2% H2S, ie. sour service n Post Weld Heat Treated (stress relieved) n Design: 350kPa & 450oC n Operating: 55kPa & ~75oC n Uninsulated n Internally coated from ~10 years into service life n Measured average general Corrosion Rate ~0.05mm/yr n Remaining Life from general corrosion (“wastage”) >>20yrs n Pitting Corrosion Rate ~0.5mm/yr prior to internal coating, now largely mitigated
  15. 15. 45C-612 & 45C-612A – application of RBI Via use of Capstone RBMI program: n External corrosion risk low – uninsulated, external coating good n Internal corrosion risk low – reflects in CR & RL calculation n For water + 20,000ppm H2S & PWHT, API 581 App.H assigns Low susceptibility to Wet H2S cracking è entered into Capstone RBMI n “Low” is not zero! Capstone RBMI calculates: – Medium risk of cracking for C-612A, because of MPI testing in April 1996 – Medium-High risk of cracking for C-612, because it had never been inspected for cracking
  16. 16. Aside – effectiveness of stress relief (PWHT) US experience (large statistical sample): n History of cracking in SR/PWHT vessels n Loosely specified n Inadequate QA
  17. 17. 45C-612 & 45C-612A – application of RBI n 45C-612 is the vessel due for inspection based on risk n 45C-612A is the vessel due for inspection based on time n Cracking, rather than corrosion, is the highest risk for both vessels n Visualinspection does not effectively address cracking
  18. 18. 45C-612 & 45C-612A – calculated risk levels @ 2003 45C-612 45C-612A
  19. 19. 45C-612 & 45C-612A – 2003 inspection regime n 45C-612: Ø external shearwave UT of 100% of welds è Highly Effective inspection for Wet H2S cracking per API 581 Table H-4C è no defects n 45C-612A: Ø spot external thickness gauging è Fairly Effective inspection for Thinning per API 581 Table G-6A è confirms low corrosion rate Ø credit claimed for representative cracking inspection è AS3788 4.4.4.6 allows representative inspection of parallel equipment è Usually Effective inspection for Wet H2S cracking per API 581 Table G-6A (one level lower than for vessel inspected)
  20. 20. 45C-612 & 45C-612A - results n Reduction in OH&S risk (H2S 45C-612 & C-612A risk @ 2011 exposure) n Saving & deferral of estimated $60K expenditure n Inspection period for both vessels extended to 2011 with no significant increase in risk (Capstone RBMI “What if?” analysis - lookahead)
  21. 21. 45C-612 & 45C-612A - lessons n Corrosion is not the only, or even the most important, deterioration mechanism – this leads to some (initially) surprising results n Visualinspection may not be the best way to mitigate all deterioration risks – can do an “effective” inspection without entry n PWHT may not eliminate the risk of environmental cracking! n API 581 allows quantification & comparison of cracking risk with other risks
  22. 22. 45C-612 & 45C-612A - postscript n Internalinspection of 45C-612 & 45C-612A as part of Kurnell Clean Fuels upgrade n Found cracking in 45C-612 – Fabrication defects? – Missed by shearwave, or appeared since 2003? n Justifies requirement for crack testing n Capstone RBMI has an Inspection Planning tool (Last Date, Frequency, calculated Next Date) & reporting functions to ensure appropriate testing is done at suitable intervals
  23. 23. Benefits of Risk Based Inspection n5 year plant T&I schedule for 2004 on based on RBI n Various plant runlength extensions granted n Estimated saving…

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