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<Title of Presentation> By: <Author Name>, <Organization>
<Date>
17th INTERNATIONAL CONFERENCE & EXHIBITION
ON LIQUEFIED NATURAL GAS (LNG 17)
LNG VESSEL CASCADING DAMAGE
STRUCTURAL AND THERMAL ANALYSES By: Jason Petti, Sandia National Laboratories
17 April 2013
17th INTERNATIONAL CONFERENCE & EXHIBITION ON
LIQUEFIED NATURAL GAS (LNG 17)
LNG Cascading Damage Scenario
Can an LNG tank breach event cascade throughout the
tank, extend to other tanks, and experience
further damage due to an external fire?
Membrane LNG Carrier
Multi-Physics Cascading Damage Analysis Approach
Heat Transfer
Tests
Cryo Damage
Testing/Model
Development
Fire Load
F(x,t)
Structural Damage
Model
Exterior
LNG Pool
F(x,t)
Tank Draining
F(t)
LNG Flow
Analysis
Fire Tests & Analysis
Stress, Damage,
& Stability Analysis
Cryo Interior
Flow, F(x,t)
Temperatures
F(t)
LNG Cascading Damage Components
Structural Damage Analysis – Assess Cryo Damage State
Assess Effects from Fire
LNG Flow Analysis
Internal Flow External Flow
Vessel Model Development Basic Material Tests
Large Scale Fracture Tests
Damage Model Development & Calibration
LNG Heat Transfer Tests
Cooling Rates (Air and Water)
Heating Rates
Fire & Insulation Tests
Vessel Fire Analyses
LNG Ship Structural Steel Thermal Damage Issues and Concerns
LNG spills known to cause brittle fracture of ship deck plates
– Fracture testing showed LNG ship steels vulnerable to fracture at LNG temperatures
Fires reduce steel strength
– Testing showed LNG ship steel strength will be reduced to ~15% at LNG fire temperatures
Cryogenic Damage Testing TESTING GOAL: Perform tests to explore thermally induced crack
propagation. Results provide input for Damage Model.
Phase I – Exploratory small plate tests, subjected to LN2 and designed to explore testing procedures
Phase II – Small scale tests to examine crack propagation, cooling region changes, marine steels
Phase III - Large scale tests with representative vessel hull features
Also performed basic material tests (stress-strain, Charpy, CTE) for ABS Grade A and ABS Grade EH36 over -191C to 800C.
Cryogenic Damage Test Setup
Cryogenic Damage Testing
Cracked Plate Example
Cryogenic Damage Testing - Phase III Structure
Cryogenic Damage Testing - Phase III Example
Cryogenic Damage Testing - Phase III Example
Cryogenic Damage Testing - Phase III Example
Summary of Cryogenic Testing Results
Fractures occurred mainly in the LN2 flow area
– Fractures did propagate slightly outside the LN2 flow area due to cooling
Fracture initiation was observed at machined notches and structural discontinuities
– Many initiation sites exist within vessels
Mechanical pre-load (initial stress) not required to initiate/propagate fracture
– Localized cryo temperatures are enough to generate fractures given stress concentrations
Fractures propagate through all cold structural members - webs, stiffeners, flanges
Fractures can occur in structural elements in contact with water
– Depends on the current strength and other factors
Damage Model
• Fracture model produces similar qualitative fracture and damage directions and results
• Damage occurs across plates and members and secondary cracks occur
• Damage progresses up and through the side wall
Full Vessel Model Development
Used detailed drawings and information on Membrane and Moss vessels
Structural components have been explicitly represented with some simplifications in aft and forward regions
Weight distribution for non-structural items and LNG cargo are represented with appropriate loading functions
~4.5 million elements used for Moss and Membrane vessels
Moss Regions
Fore (less detail)
Mid ship (detailed
section
Aft (less detail)
Membrane
Meshing
Moss and Membrane Flow Analyses
External Flow Analyses
External LNG Pool Formation
MOSS Membrane
Above WL
~ 180m ~ 350m
Near WL
~ 205m ~ 330m
External Pool Sizes
Cooling Rate Studies
-162
-142
-122
-102
-82
-62
-42
-22
-2
18
38
0 300 600 900 1200 1500 1800 2100 2400 2700 3000 3300 3600
Tem
pe
ratu
re (
°C)
time (s)
Temp-mid (400)
Temp-edge (400)
Temp-out (400)
Temp-mid (1080)
Temp-edge (1080)
Temp-out (1080)
Two vessels examined: Membrane and Moss
Several breach scenarios evaluated for each class of ship
– based on a range of small to large breach events, these define the initial conditions for this study
Conditions analyzed are near shore, calm water
The initial load state was computed for each vessel (Summer Arrival – full load – no ballast)
Regions of LNG flow identified for both vessels
Above waterlines analyzed, but not significantly different that near waterline
The temperature of the LNG flow regions was decreased based on LNG heat transfer tests
Damage model removes elements after reaching strain/temperature criterion
LNG Cascading Damage Initial Conditions & Assumptions
Moss - Damage
Moss - Damage
Moss Section Analysis
Original Section
Fire
Cryo
Membrane – Damage
Membrane Damage
Fire and Heating Regions
MOSS: 180m
Mem.: 210m
Heating Regions
Membrane Section Analysis
Original Section
Fire
Cryo
LNG Cascading Damage Summary
Large scale fracture testing program conducted to calibrate computational damage model
Assessments performed for a number of assumed breach scenarios for each class of ship: Membrane and Moss
Each scenario included an assessment of the final damage states, small holes may be manageable, medium and large holes lead to significant damage within the vessel