LNG VESSEL CASCADING DAMAGE <Title of Presentation> - - PowerPoint PPT Presentation

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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 38 300 600 900 1200 1500 1800 2100 2400 2700 3000 3300 3600 Temperature (°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
• n 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