canada-newfoundland and labrador offshore petroleum board presenter : walter bobby icrard stavanger...

Presenter : Walter Bobby Canada-Newfoundland and Labrador

Offshore Petroleum Board

ICRARD

Stavanger

September 12, 13 2007

Walter Bobby



CanadaCanada

Additional information on the website

ICRARD



SafetyEnvironmental Criteria

IssuesDiscussion



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

IssuesSafety



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?

IssuesSafety (Contd.)



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?




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?




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




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?

IssuesSafety (contd.)



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

IssuesEnvironmental Criteria



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

IssuesEnvironmental Criteria (Contd.)



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




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




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?


canada-newfoundland and labrador offshore petroleum board presenter : walter bobby icrard stavanger...

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