Using Critical Zone Inspection and Response Monitoring To Prove Riser Condition M Cerkovnik -2H Offshore
Agenda 1. Introduction 2. High level methodology 3. Verifying condition 4. Defining requirements 5. Assessment Effects of Damage Life Prediction 6. Summary and recommendations August 30 - September 1, 2016 6 th Annual Global FPSO Forum
Introduction Life extension Continue the service of assets beyond the original design life Field life extension will need to cover Risers and Subsea components No established guidance available for US assets. A general guidance from O&G UK is available August 30 - September 1, 2016 6 th Annual Global FPSO Forum
Aging Assets Percent Exceeding 20 Year Age by 2020 Africa GOM Brazil Asia North Sea 0 5 10 15 20 25 30 35 40 Percent
High level methodology for life extension Verify condition Define the extended service requirements Check the original design assumptions against current knowledge Assess Fatigue Corrosion Degradation
Key Issues Verification of condition Fatigue life Material degradation Uncertainty of requirements Flexible riser condition
SCR Condition Verification Threat External corrosion Internal corrosion Damage Degradation of Flexjoint Degradation of CP Degradation of coatings Fatigue Verification Visual inspection Full ILI Critical Zone Radiography Targeted ILI Corrosion modelling Visual Inspection Visual Inspection CP survey Visual inspection Visual inspection Loads Monitoring Vessel Motion Monitoring Response Monitoring Metocean Tracking
Condition Assessment To determine the current status of risers: Corroded pipe Corrosion defects Missing strakes Severe marine growth Damaged coating Higher environmental data Etc.
Verifying internal condition if full length ILI is not possible Radiographic local inspection CT scans Partial ILI Tethered Subsea pig launch Down and back Corrosion Modelling
Local Radiographic Radiographic methods can be employed to verify the wall thickness. This method is not a practical way to inspect an entire flowline, but it can be a very good way to determine the condition of the pipe at a sampling of critical areas. For example low spots in a flowline are corrosion critical areas because they tend to attract debris and water dropout.
Relying on corrosion modelling Requires data on contents, pressure and temperature from beginning of service Models must be verified for service conditions to be credible.
Fatigue For many sites the Metocean data has changed in the last 20 years. Sometimes the data shows decreased threat; but sometimes the threat increases. There is no code based justification for relaxation of safety factors Calibration of models based on monitoring is the most likely approach to refinement.
Measuring Riser Response
Comparing Measurement to Predictions
Monitoring can be temporary or permanent Temporary used to confirm response, understand behavior, or calibrate numerical models Permanently installed monitoring is used to assure integrity. Acoustic modems used to transmit tension 18
Fatigue + Corrosion Crack growth rates increase in corrosive environments If corrosion is present in lines the fatigue analysis will need to account for it
Analytical Assessment Based on current condition and the latest loading information Tension requirements Strength analysis and hurricane acceptability Fatigue analysis Wear analysis Fitness for service Etc.
Conclusions 1. Life extension for risers starts with verifying the condition 2. Full ILI is the best option to verify condition but local inspection of critical areas together with corrosion modelling can be compelling. 3. Fatigue damage models can be improved by monitoring 4. Corrosion fatigue analysis is best done using FCG methods August 30 - September 1, 2016 6 th Annual Global FPSO Forum