FPSO Research Forum Forum Discussion OTRC, College Station USA April 2003

Korea Mar 03DNV Houston background Slide 2 Corrosion issues and challenges 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 Optimal vs. minimal requirements

Corrosion protection

Korea Mar 03DNV Houston background Slide 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

Maintenance, repair & planning strategies

Korea Mar 03DNV Houston background Slide 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

Korea Mar 03DNV Houston background Slide 7 Cargo Tank 0.5tk = 0.5mmBallast Tank 0.5tk = 1.0mm Material235MPa315MPa235MPa315MPa Long. Spacingt min 900mm16.6mm17.8mm18.0mm19.3mm Typical VLCC2021 Δ3.4mm (17%) 2.2mm (11%) 3.0mm (14%) 1.7mm (8%) 2 – 3mm reduction in main deck plate will reduce buckling capacity 10-15% t k = 3.0mm (ballast tank) = 14% of actual plate thickness = 14% of actual plate thickness Corrosion impact - Buckling

Korea Mar 03DNV Houston background Slide 8 DNV’s acceptance criteria options Thickness measurements  Repair to As-built - Easy to determine - Quick (WSD) Pass/fail No action  Repair to WWT - Requires simple calc - Medium time (WSD)  Repair to Site - Rigorous calc - Time consuming (LRFD) Which is the cost effective solution?

Korea Mar 03DNV Houston background Slide 9 Color Coded Model Thickness Measurements Import Thickness Measurements

Korea Mar 03DNV Houston background Slide 10 “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 Compare against requirements

Different environmental & operating conditions

Korea Mar 03DNV Houston background Slide 12 Different environmental & operating conditions 90% of future FPSOs are forecast to be in non-harsh environments but…

Korea Mar 03DNV Houston background Slide 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)

Korea Mar 03DNV Houston background Slide 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.