Presentation given in the SNAME Offshore Symposium, February 2018, Houston, Texas

1. The 23rd Offshore Symposium
Feb 14, 2018 | Houston, Texas
www.snamesymposium.com
A BRIEF REVIEW OF ROBUSTNESS
EFFORTS IN THE OFFSHORE INDUSTRY
Alberto Morandi
GustoMSC
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2. Robustness
A robust process or system will accommodate
(reasonably foreseeable) perturbations and variability
without disproportional loss of functionality and in a
(cost) efficient manner.
My calculator Voyager 1

3. It all starts with Reliability
•A philosophy of strength factors relating both to
accident rates — to bring into better perspective some
of our past problems, to point to ways of further
development, and to prepare for making the fullest
use of loading statistics now accumulating.
•Sir Alfred G. Pugsley, 1930s & 40s
•Airplanes: higher stresses on materials
with no defined fatigue endurance limit
– Frequency of occurrence of loads of different
magnitudes
– Variability in material strength

4. The 23rd Offshore Symposium
Reliability & Limit State Design
(Generally at Component Level)
Pioneers:
• C.A. Cornell (1967)
(pictured)
• Hasofer-Lind (1974)
• Rackwitz-Fiessler (1978)
• Breitung (1984)
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5. The 23rd Offshore Symposium
Parallel Development in Standards
•Joint Committee on Structural Safety
(JCSS), 1971, unified set of rules
(1978) and later Eurocode (1984)
– Pioneer: Julio Ferry Borges (pictured)
•Norway NKB 1978 (Building), NORSOK
•Denmark DS 415 (Geotechnical), 1978
– Pioneer: Jørgen Brinch Hansen (pictured)
•Canada CSA (Steel Buildings) 1974
•USA, LRFD research 1960s / 1970s,
AISC LRFD 1998
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6. The 23rd Offshore Symposium
Practical Challenges
Alfred M. Freudenthal (1954): ‘Safety is deeply rooted
in engineering design and the notion of failure probability
is repulsive to a majority of engineers’
•Modeling limit states requires advanced analysis
•Statistics and probability theory require lots of
data and are unfamiliar to structural engineers
•Notional results too sensitive to assumptions for the mean and
variance of the key variables
•The payoff in structural efficiency is not always convincing
•Reconciling design safety margins with observed failure rates is
complicated by non-structural factors
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7. A Key Concept: Hazard Curve
Random
Variability
Bias

8. Low Probability & High Consequence
Hurricane Harvey flooding:
- Climate change?
- Changes to land use?

9. The 23rd Offshore Symposium
Observations for Offshore Structures
Hurricane Rita
Tie-back & other brownfield expansion
Jack-up ‘legging-up’
Climate: Abnormal events
impacting an expanding fleet
Structural changes:
Upgrade with care!
Hurricane Lili
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10. Non-Structural Factors
Troll Solution
Perro Negro 6Thunder Horse
Petrobras P36
Macondo Incident

11. Creating System Load Paths
1903 – Wright Flyer I 1906 – Santos Dumont 14-Bis
CJ70
Pushover
Analysis in
ABAQUS
CJ70 - Noble Lloyd Noble (Courtesy Noble Drilling)

12. Reliability of Fixed Platforms
New
Manned
non-
evacuated
Environment Action*
factor
Mean
RSR
AUS 1.59 2.18
NNS 1.40 1.92
CNS & SNS 1.26 1.73
New
Unmanned
Environment Action*
factor
Mean
RSR
AUS & GOM 1.17 1.60
NNS 1.09 1.49
CNS & SNS 1.02 1.40
* With 100-year joint probability metocean data
Efthymiou & van de Graaf [1997]
UK HSE Benchmark: Pushover
Analysis of Shell Kittiwake,
Morandi & Frieze, 1997

13. The 23rd Offshore Symposium
SNAME T&R 5-5A to ISO 19905-1
UK HSE – Global Maritime 2003
P. Marshall – R. Hunt 2001
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14. Reliability in ISO 19900 (DIS 2018)
Hazard
Curves!

15. The 23rd Offshore Symposium
Robustness in ISO 19900
•ISO 2394 (General Principles of Reliability): ability of a
structure to withstand adverse and unforeseen events
(like fire, explosion, and impact) or consequences of human
errors without being damaged to an extent disproportionate
to the original cause.
•ISO 19900 (General Requirements for Offshore
Structures): ability of a structure to withstand accidental
and abnormal events without being damaged to an
extent disproportionate to the cause.
•ISO 19902 (Fixed Structures): ability of a structure to
withstand events with a reasonable likelihood of
occurring without being damaged to an extent
disproportionate to the cause.
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16. Defense in Depth (ISO 19900)
Bow Tie Diagram
Reduction of the probability that the action occurs or reduction of the action intensity
(e.g. prevention through inherently safe design, material specs, integrity management,
risk management, monitoring, inspection, disconnection, etc.);
Reduction of the effect of the action on the structure (e.g. protection through ice
management, vessel heading changes, floater draft adjustment and slacking of
mooring lines, etc.);
Migitation of the consequences of failure (evacuation, shutting down wells, emergency
response, isolation and containment, etc.)

17. Monitoring for jack-ups
going on- and off-location
The Role of Digitalization
Data-driven Operations & Opportunities to Intervene
Liberty Mutual
RightTrack®

18. The 23rd Offshore Symposium
Robustness needs clearer guidance
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