Life extension of existing offshore structures

1
Life extension of existing offshore structures
ISO/TC 67 N 896 Annex B

• ISO TC67 Man Com
• Rio de Janeiro
• October 2004
• Helge I Vestre, PSA Norway

2
Brief status/update re action 02MC-09

• Ph D student in PSA completes thesis on different
  approaches to designlife extension summer 2005
• PSA have resently received spesific applications
  on extension of design life
• HSE have developed check list in cooperation with
  Cranfield activities/evaluations/calculations
• PSA have positive experience with check-list for
  floaters/drilling- accomodation rigs
• SC7 19902 now includes requirements related to
  possible designlife prolongation
  (milestone-activities)
• API starts development of standard on designlife
  extension? (ref R Snell)
• SC2 New convenor in WG13. No progress on state
  of the art reported

3
Age distribution of offshore installations has
not changed
4
We do not want this to happen due to age
OTC 16801
5
Example Crack growth
cracks
Cr. growth stopped after insp repair
T
6
Definition of life of a structure

• Life of structure until design life is reached
• For damage tolerant structures the safe life is
  reached when the probability of simultaneous
  failures exceeds a safe level before they are
  found and repaired.
• For not damage tolerant structures the safe life
  is reached when the probability of single
  failures exceeds a safe level before they are
  found and repaired

7
Elements in handling of life extension

• Check condition against drawings and computer
  models
• Update fatigue analysis
• Check robustness wrt to damaged condition
  (overload and fatigue)
• Reassessment of inspection program and the need
  for repairs
• Evaluate experience from incidents and accidents
• Establish potential hazards, failure modes,
  barriers, barrier indicators, and acceptance
  criteria. Establish methods to monitor these
  barrier indicators.
• Evaluate simultaneous failures and additional
  acceptance criteria for the barriers
• Estimate a safe life for the structure /
  installation

8
Interesting questions

• Does API plan to develop a standard on designlife
  extension
• If Yes
• Will the scope be relevant for SC2 and SC7 (or
  others)
• Could early cooperation/koordination be an idea
• Could synergies be achieved both for API and ISO
• What about doing it once, right and
  internationally ?

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Summary

• Increasing number of aging structures both on
  NCS, UKCS and GOM (world-wide)
• Aging structures are a potential hazard, and an
  asset if kept operational, and should be treated
  differently from structures in their original
  design life.
• The challenge is fully accepted and documented in
  resolutions in ISO TC67/SC2 and SC7
• Authorities will continue to handle consent
  applications from case to case
• Early cooperation API/ISO could bring synergies
  to both parties