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FPSO Research Forum Forum Discussion

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FPSO Research Forum Forum Discussion. OTRC, College Station USA April 2003. Corrosion issues and challenges. Optimal vs. minimal requirements. Corrosion protection Corrosion margins Coating types Maintenance, repair & planning strategies Repair or replace? Now or later?

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FPSO Research Forum Forum Discussion

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  1. FPSO Research ForumForum Discussion OTRC, College Station USA April 2003

  2. Corrosion issues and challenges Optimal vs. minimal requirements • Corrosion protection • Corrosion margins • Coating types • Maintenance, repair & planning strategies • Repair or replace? • Now or later? • Owner/Operator vs. Class vs. Regulatory • Balancing economic vs. safety vs. environment • Different environmental & operating conditions DNV Houston background

  3. Corrosion protection

  4. Corrosion Protection • Coating: • Critical but expensive: • Application (fabrication schedule impact) • Inspection (construction and in-service) • Class focus during operation but not (normally) NB • Note: Cannot coat steel with steel • Anodes • Significant weight and cost. Can we optimize? • Impressed current Which provides the best economic return? CAPEX vs. OPEX DNV Houston background

  5. Maintenance, repair & planning strategies

  6. Corrosion impact • Leaking: • Gaseous vapors  explosion • Pollution • Fatigue: • Lives halved in corrosive environment(corrosion is located at HS) • General corrosion has less impact • Yield strength: • typically small impact Typically local impact only DNV Houston background

  7. Corrosion impact - Buckling tk = 3.0mm (ballast tank) = 14% of actual plate thickness 2 – 3mm reduction in main deck plate will reduce buckling capacity 10-15% DNV Houston background

  8. DNV’s acceptance criteria options Thickness measurements Pass/fail No action • Repair to As-built • Easy to determine • Quick (WSD) • Repair to WWT • Requires simple calc • Medium time (WSD) • Repair to Site • Rigorous calc • Time consuming (LRFD) Which is the cost effective solution? DNV Houston background

  9. Import Thickness Measurements Thickness Measurements Color Coded Model DNV Houston background

  10. Compare against requirements “As-built” or “As Measured” Plot Thickness Distribution Curves (S-Curves)(Tanker Structure Cooperative Forum & DNV) Prediction of Steel Diminution • Generate repair specifications • Establish volumes, weights, areas & staging • Store all collected information for analysis and later re-use DNV Houston background

  11. Different environmental & operating conditions

  12. Different environmental & operating conditions 90% of future FPSOs are forecast to be in non-harsh environments but… What is a "harsh" environment for corrosion? DNV Houston background

  13. Questions for discussion • Should we focus on: • Corrosion protection systems? (Preventative), or • Monitoring, recording & decision making systems? (Reactive) • What information do we need: • Corrosion margins • Corrosion rates • How do we address and rank the variables? • Cargo type, temperature, steel type, etc. • How do we incorporate into the Life Cycle: • Design • Fabrication inspection • Inspection and Maintenance Planning • Repair decisions • Feedback / Industry updates (ownership) DNV Houston background

  14. Reference DNV Guidelines • Classification Notes 72.1 Allowable Thickness Diminution for Hull Structure, November 2000(currently being updated) • RP Corrosion Protection of Ships, 2000 • Classification Notes 33.1, Corrosion Prevention of Tanks and Holds, July 1999. DNV Houston background

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