ndc presentation _ stability for jackups a new challenge
DESCRIPTION
Stability knowledge on jackups is often not given the importance it deserves. This presentation that was made at the Offshore Jackup Middle East Conference in 2013 raises some important questionsTRANSCRIPT
7/18/2019 NDC Presentation _ Stability for Jackups a New Challenge
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Stability for Jackups
A Different
Challenge
Oct 9 2013
Presented by Arun Pushkarna
Asset Integrity Manager
National Drilling Company Abu Dhabi
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Before We Start
7/18/2019 NDC Presentation _ Stability for Jackups a New Challenge
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Let’s Journey Back in Time
Early Assyrian Warship, possibly 8th Century BC
Triremes designed for low Centre of Gravity, high freeboard
Stability awareness existed at that time
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Journey in Time … contd
• Earliest oceangoing
vessels appeared in 2000B.C
• 250 BC: Archimedes
propounded the Laws of
Flotation
• 1746 – 49: Bouguer & Euler
established hydrostatic
stability criteria
• 1860: John Rusell formed
Institute of NavalArchitects
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Journey Continues
• 1867: 2350 Seamen & 137passengers died
• 1876: Compulsory Plimsoll mark on
British ships
• 1890: Marking of loadlineaccording to measurement
mandatory
• 1930: Loadline rules formulated
based on freeboard
• 1966: IMO adopted Loadline Rules
based on subdivision and damage
stability
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IMO Code on Intact Stability
Preamble
“…..the safety of a ship in a seaway involves complex
hydrodynamic phenomena which up to now have not
been adequately investigated and understood…..
….. It is recognized that development of stability
criteria, based on hydrodynamic aspects and stability
analysis of a ship in a seaway, poses, at present,
complex problems which require further research”
4013 Years ……..and Counting!!!
7/18/2019 NDC Presentation _ Stability for Jackups a New Challenge
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Let’s Agree on the Definition
StabilityThe ability of a ship to regain
its upright equilibrium position,
after the removal of external
factor which caused the vessel
to heel at an angle.
Ships are stable when upright
Ships by design need to be afloat
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Ships Vs Jack Up Rigs
SHIPS
• Appeared in 2000 B.C
• Spend 99% of time afloat;
1% drydocked
• Water supported• Ships have certified,
licensed Officers
• Has taken 4000 years for
developing stability
JACKUPS
• Appeared in year 1954
• Spend 98% time jacked up;
2% time afloat
• Soil supported• Few regulatory
requirements
• In our Lifetime…???
7/18/2019 NDC Presentation _ Stability for Jackups a New Challenge
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IMO Codes on Stability
Guidance for MODUs
contained in
• Code for Intact
Stability
• MODU Code
Conditions covered by
Codes
– Operating Conditions
– Severe Storm Condition
– Transit Condition
7/18/2019 NDC Presentation _ Stability for Jackups a New Challenge
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So……
Are we on Solid Ground?
7/18/2019 NDC Presentation _ Stability for Jackups a New Challenge
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2002: This Unit Met Stability Criteria
Jacking system slipped and the hull fell heavily on one side causing
the Port side to drop down with catastrophic consequences
Was the Rig “Stable”?
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2009: So Did This
This rig was preloading when the leg penetrated in soil
causing serious leg and hull damage
Was it “Stable”?
7/18/2019 NDC Presentation _ Stability for Jackups a New Challenge
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Three Months Ago
• Tragic consequences ofloss of soil stability
• Damage caused
uncontrolled flooding
• Rig sank in a short time• It was a MODU and
Stability compliant unit
Why did it get lost?
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The Jackup Difference
• Jackup Rigs are designed to be supported on legs
• Most of their lifespan is in elevated mode
• Risks of loss of “stability” is equally high on location
• Staff frequently experienced but not certified
• No prescriptive standards to appreciate risks
• Soil understanding almost nil
• Codes do not address the requirements
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IMO Requirements
All personnel on mobile offshore
units
As soon aspracticable
MOU
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IMO: OIM Requirements
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What Needs to Change
• Understanding of soil strength
imperative to foundationstability
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Generally Overlooked
• Attachments to legs e.g.,ladders, pipes, etc
• Marine Growth on legs
and drag due to same
• Helicopter landing loads
• Mooring loads for Supply
vessels
• Unbalanced leg loads due
to high drilling fluid
changes
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The Challenges Remain
• Guidance is strongly inclined totransit condition.
• Assumptions of storm calculations
never placed on board
• Guidance to soil testing/preloadingonly weakly referenced in
Operating Manual
• Competency requirements now
defined but lacking details
• No development paths exist
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Stark Reminder: Unsinkable Titanic (1912)