ICRARD

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• ICRARD
• Stavanger
• September 12, 13 2007
• Walter Bobby

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Canada

• Additional information on the website
• ICRARD

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Discussion
Issues

• Safety
• Environmental Criteria

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Issues

• HELP!

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Safety
Issues

• SIL used
• Application of IEC 61508 and IEC 61511
• IEC 61508 Part 6
• Reliability of a SIL loop is a function of the
  components reliability and test period of the
  components
• component failure rates are constant over the
  life of the system
• Reliabilities of valves normally dormant (shut
  down valves, blow down valves) are dependent on
  test frequency of the valve. Therefore, their
  failure rates are not constant

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Safety (Contd.)
Issues

• SIL used (Contd.)
• Is there a need to review the application of IEC
  61508 and IEC 61511 for valves normally dormant
  (shut down valves, blow down valves)? The
  reliability of such valves are dependent on the
  frequency of testing.
• How should IEC 61508 and IEC 61511 be applied for
  components whose failure rates are dependent on
  testing frequency?

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Safety (Contd.)
Issues

• A QRA is done to verify that the target level of
  safety is achieved.
• API RP 14C defines the emergency shut down valve
  as part of a primary system
• Should the reliability (frequency of failure) of
  the emergency shut down valve be verified on an
  ongoing basis?
• How does the frequency of failure of the
  emergency shut down valve influence the QRA?

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Safety (Contd.)
Issues

• Target reliability for subsea systems
• Failure of subsea systems affects safety
• For people marginally
• For the environment significantly
• Repair of subsea systems may affect safety
• For people significantly
• For the environment marginally
• Should the target reliability for subsea systems
  be the same as for a manned installation?

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Safety (Contd.)
Issues

• Concept of safety envelope
• Risks associated with repair is normally not
  included in QRA
• Sometimes the risk associated with repair is
  comparable or more than during normal operation
• Repairs increase project duration and hence the
  duration of exposure to risk

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Safety (contd.)
Issues

• Concept of safety envelope (Contd.)
• For some hazards such as noise and thermal
  radiation, acceptable levels are a function of
  time of exposure to the hazard, e.g., less than 1
  hour for level of sound of 105 dB
• Should criteria be established for the integral
  of risk and time of exposure?

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Environmental Criteria
Issues

• Accelerated fatigue noticed on the Grand Banks
• Semi-submersibles are designed for 100 year
  environmental criteria
• A lesser return period for beam seas is used if
  it produces higher stresses
• Grand Banks experiences cross seas

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Environmental Criteria (Contd.)
Issues

• Should additional load combinations be included
  in design for cross seas?

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Environmental Criteria (Contd.)
Issues

• Rare environmental events. CSA S471 states
• Specified loads based on frequent environmental
  processes shall have an annual probability of
  exceedance, PE, not greater than 10-2
• Note For practical reasons, a probability of
  exceedance, PE, of 10-2 per annum is generally
  used to choose a process of defined magnitude
  rather than, as would ideally be the case, to
  choose a load resulting from processes of
  different magnitudes that occur with different
  probabilities.
• specified loads based on rare environmental
  events shall have an annual probability of
  exceedance, PE, within the range of 10-4 to 10-3

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Environmental Criteria (Contd.)
Issues

• Iceberg considered both as frequent environmental
  processes and as rare environmental process
• Iceberg loads generated based on probability
  distribution of shape, mass, velocity,
  eccentricity etc.
• 500 year and one in 10-4 values were determined

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Environmental Criteria (Contd.)
Issues

• It is possible for an iceberg to be in the
  vicinity of the installation that could cause
  loads in excess of the 500 year load value
• How can this be captured in the design criteria?

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• Thank You