1. Analytical Technique for Composite Storage Tank
Design Factor Specification
NHA Annual Hydrogen Conference 2008 March 30 - April 4, Sacramento, CA
Vladimir M. Shkolnikov, Ph.D., CTC
Kevin L. Klug, Ph.D., CTC

2. AGENDA COMPOSITE OVERWRAPPED PRESSURE VESSELS
DEVELOPMENTAL GOALS & REQUIREMENTS
ACCOMPLISHMENTS TO DATE
CONCERNING ISSUES
REQUIREMENTS VARIANCE
DETERIORATIVE FACTORS OF OPERATION
DESIGN STRENGTH RECONCILIATION TECHNIQUES
EXEMPLIFIED SERVICEABILITY ASSESSMENT
DESIGN FACTOR SPECIFICATION

3. Composite Overwrapped Pressure Vessels (COPV)
COPV Type 3, metal-lined composite reinforced cylinder with load-sharing liner that alone cannot resist the operating pressure, normally termed full-wrapped.
COPV Type 2, metal-lined composite reinforced cylinder with load-sharing liner that alone can withstand the operating pressure, normally termed hoop-wrapped.
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4. DOE Goals & Requirements
Develop and demonstrate viable hydrogen storage technologies for on-board and off-board applications
By 2010: Develop and verify hydrogen storage systems achieving 2 kWh/kg (6 wt%), 1.5 kWh/L, $4/kWh, and 30 g/L; storage tank purchased capital cost $500/kg H2; ambient -30/50ºC + full solar load; min/max delivery temperature -40/85ºC; life (1/4 tank to full) 1000 cycles
By 2015: Develop and verify hydrogen storage systems achieving 3 kWh/kg (9 wt%), 2.7 kWh/L, $2/kWh, and >35 g/L; storage tank purchased capital cost $300/kg H2; ambient -40/60ºC + full solar load; min/max delivery temperature -40/85ºC; life (1/4 tank to full) 1500 cycles.

5. COPV Type 3 Designed and produced by HyPerComp Engineering, Inc.
(Brigham City, UT) for DOE project with CTC
COPV-3 prototype with aluminum liner for on-board application
Capacity: 7.75 L (0.30 kg H2)
Mean burst test pressure: 25.4 Ksi
Intended service pressure: 10.0 Ksi
Hydrogen weight efficiency: 5.2% (6 wt% for 2010)
Hydrogen volumetric efficiency: 38.7 g/L (30.0 g/L for 2010)
Estimated cost: $4,700/kg H2 ($500/kg H2 for 2010).
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6. COPV Type 2 Designed and produced by HyPerComp Engineering, Inc.
(Brigham City, UT) for DOE project with CTC
COPV-2 prototype with steel liner for off-board application
Capacity: 15.1 L (0.44 kg H2)
Mean burst test pressure: 15.5 Ksi
Intended service pressure: 6.2 Ksi
Hydrogen weight efficiency: 2.4% (6 wt% for 2010)
Hydrogen volumetric efficiency: 29.2 g/L (30.0 g/L for 2010)
Estimated cost: $641/kg H2 ($500/kg H2 for 2010)
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7. Concerning Issues
The DOE goals and requirements, while presenting good reference points for COPV advancement, are incomplete in terms of design criteria for verification of long-term COPV capability
Polymer Matrix Composites (PMC) typically exhibit enhanced sensitivity to time-variable parameters of force - temperature exposure that should be taken into account
Existing standards / codes don’t provide design guidance sufficient to characterize serviceability and/or properly select a design factor for COPVs subjected to changeable operational exposure.

8. Requirements Variance
Criteria
Material
CGA [1]
ISO [2]
DOT [3]
Stress ratios:
Burst/test
(Burst/service)
Aramid FRP
2.0 (3.0)
2.1 (3.51)
2.04 (3.4)
Carbon FRP
1.5 (2.25)
2.0 (3.34)
Glass FRP
2.33 (3.5)
2.4 (4.01)
Service life
30 years
30 + years
15 years
CGA C -19 FRP-3.– Guideline for Filament-Wound Composite Cylinders with Nonloadsharing Liners, Second Edition. Compressed Gas Association, Inc., 2002
ISO : Gas Cylinders of Composite Construction - Specification and Test Methods - Part 2: Fully Wrapped Fiber Reinforced Composite Gas Cylinders With Load-sharing Metal Liners, 2002
DOT-CFFC. Appendix A. Basic Requirements for Fully Wrapped Carbon-Fiber Reinforced Aluminum Lined Cylinders
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9. Principal Objective
Improve methodology for serviceability * characterization and specification of design factors to ensure proper long-term performance of COPVs.
* Prerequisite quality of service accomplished within a specified timeframe.

10. Deteriorative Factors of Operation
Over-the-road bulk transportation
Stationary accumulators for gas generation and/or collection sites
Stationary storage for forecourt dispensing sites
As an end-user’s vehicular fuel tank.
These applications imply a variety of duty cycles and loading factors which will affect long-term structural performance of composite wrap jacket of COPV.  
Storage tanks will be employed for assorted engineering systems of Hydrogen Infrastructure including:
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11. Deteriorative Factors of Operation
* A fabrication technique in which COPV is subjected to high pressure, causing the metal liner to yield and resulting in its compressive residual stresses. The goal of autofrettage is to increase the liner’s durability.
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12. Temperature Factor Possible Effects
Temperature may affect the composite jacket of COPV in several ways:
As a direct deteriorative factor of thermal-mechanical fatigue
Via increase of pressure of the contained gaseous hydrogen
Inducing additional interface pressure between the jacket and load-sharing liner due to difference in thermal expansion of the jacket and liner materials.
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13. Temperature Factor Outside Ambient Temperature
Off-board storage tanks can sit at any climatic zone either above ground, on, or underground. This entails a wide variety of outside ambient temperatures during operation as no temperature control is present.
Filling stations in North America
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14. Temperature Factor Pressure-Temperature-Density Interdependency*
H2 density vs. pressure & temperature
Pressure increase due to H2 heating
* - NIST Standard Reference Database,
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15. Temperature Factor Fast Filling • Warming up
The approximation is based on experimental data* regarding pressure & temperature changing over filling time and is to be utilized within COPV serviceability assessment.
Approximated P,T = f (time)
* - Eihusen, J. A., Application of Plastic-Lined Composite pressure vessels for Hydrogen Storage, GD Armament and Technical Products, Lincoln, NE
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16. Temperature Factor Thermal Expansion
Thermal expansion vs. temperature*
Possible outcomes
The difference in thermal expansion may affect jacket-liner interface pressure either increasing or decreasing the jacket stressing and resulting respectively with:
Liner’s elastic instability and
Reduction of residual after autofrettage pressure possibly affecting the interface bonding (when the tank is empty).
Either case lowers liner’s functionality.
* - Marquardt, E.D., Le, J.P., and Radebaugh, R., Cryogenic Material Properties Database, NIST, The 11th International Cryocooler Conference, Keystone, CO, June 20-22, 2000.
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17. Structural Design Reconciliation Conventional Technique
Allowed stress corresponds to stress ratio specified in COPV Design Guidance
Knock - down coefficients ki represent partial deteriorative influence of operational loading factors: repetitive/sustained Force (pressure), elevated Temperature, Humidity, Aggressive environment, and UV irradiation among possible others
Safety factor is a function of design uncertainties: actual Operational conditions, imperfection of utilized computer Model, and scattering of Properties of a real material system utilized within COPV structure
Guide for Building and Classing Naval Vessels, Part 1: Hull and Structures, Chapter 4: Composites, ABS, July 15, 2004
Smirnova, M.K., Paliy, O.M., Spiro, V.E., Principles of Strength Criteria Specification for Ship Structures of PMC, Mechanics of Polymer Materials, Riga, Latvia, March, 1984, p
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18. Structural Design Reconciliation Advanced Technique
Durability under assorted loading: for Pijk fraction of service exposure to ijk loading conditions (i - category of operational exposure regarding j - load case under k - temperature)
Durability under ijk exposure in terms of Kinetic Theory of Fracture
Accumulated micro-damage (deterioration) with Bailey’s Integral
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19. Fatigue data actual and standardized
Serviceability Assessment Technique Experimental Verification
Fatigue data actual and standardized
Actual loading:
Single loading rates
0.3…13.0 MPa/s (43.5…885 psi/s)
Cycling frequencies
0.03 … 0.50 Hz
Maximal cyclic stress
(0.6 … 0.8) SU
Temperature … 30°C (66 … 86°F)
Base-line loading:
Cycling frequency 0.1Hz
Stress range 0.1
Temperature 20°C (68°F)
* - Lavrov A.V. and Shkolnikov, V.M., Experimental Research of Fatigue of Thick-walled PMC Structures, Structural Application of PMC, Russian Society of Naval Engineers, v. 510, St. Petersburg, Russia: 1991, p.4-15.
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20. Serviceability Assessment Technique Influence of Loading Waveform
Typical cyclic loading waveforms
Glass FRP fatigue performance under
Cycling frequency 0.1Hz
Stress range 0.1
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21. Burst pressure in function of loading profile & rate
Serviceability Assessment Technique Single (Burst Pressure) Loading Evaluation
Burst pressure in function of loading profile & rate
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22. Serviceability Assessment Exemplified Operational Profiles
* Per CGA C-19 – FRP-3 – Guideline
** Once per week
*** Fraction of service life (%) except as otherwise noted
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23. Serviceability Assessment Prorated Influence of Service Loading
Severe loading conditions
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24. Serviceability Assessment Prorated Influence of Service Loading
Mild loading conditions
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25. Serviceability Assessment Prorated Influence of Test Loading
* - Autofrettage pressure is included into all loading profiles and is referred as Load case #1
Per Test Protocol of CGA C-19 – FRP-3 – Guideline
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26. Serviceability Assessment Prorated Influence of Test Loading
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27. Serviceability Assessment Prorated Influence of Test Loading
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28. Serviceability Assessment Summary
* Continuous service with stress ratio δP = 3.5
** To endure 30-year continuous service
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29. Serviceability Assessment Summary (continued)
Loading parameters significantly affect length of COPV service life and should be taken into account
Notable mismatch between computed and specified stress ratios substantiates the need for improvement of the design methodology
The nomenclature of design qualification tests should be selected corresponding to assigned COPV operation
Not being reconciled against actual / assigned operational conditions COPV’s serviceability might be either greater or lower than required.
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30. Design Factor Specification
It is possible to specify the knock-down factors on a pro-rata basis employing the proposed serviceability assessment technique
Safety factor should be added to cover the multiple uncertainties in loading parameters, PMC properties, and COPV computer modeling
Safety margin should be aligned with a selected loading profile; when this is close to actual or anticipated loading conditions, the safety margin might be reduced.
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31. Conclusion Remarks
The outlined technique meets the demand and is applicable regarding both operation and testing
The technique is also capable to specify a testing protocol adequately to the required COPV durability and to support COPV health monitoring in service
Dependable data on fatigue parameters of employed structural materials are needed to fulfill the serviceability assessments
The technique will somewhat complicate the conventional design reconciliation procedure; however, this extra effort will be paid off with increased performance predictability and ensured operational safety.
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32. ACKNOWLEDGEMENTS
The presented work is performed under R&D project sponsored by the U.S. DOE, award # DE- FC36-04GO14229.
The sponsorship and guidance for this project provided by Monterey Gardiner and Paul Bakke of the DOE are gratefully acknowledged.
The presented work has benefited from support of David K. Moyer and Eileen M. Schmura of CTC, former and current managers of the project, respectively.
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33. Thank you Questions / Comments?
CONTACT INFO:
Dr. Vladimir M. Shkolnikov
Tel: (814)
Dr. Kevin L. Klug
Tel: (910)
Thank you
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34. Back-up
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35. Project Relevance Hydrogen Regional Infrastructure Program in Pennsylvania
Hydrogen Fuel Cells Infrastructure and Technology (HFCIT) Program
Multi-Year Research, Development and Demonstration Plan (MYRD&DP)

36. COPV-3 Prototype
The selected COPV-3 has an aluminum (6061-T6) liner fully wrapped by fiber/epoxy PMC. The intermediate modulus Toray T K carbon fiber is chosen for PMC wrapping jacket.
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37. COPV-2 Prototype
Commercial grade Toray T700 12K and Epon 828, an epoxy resin were selected for the PMC jacket. High strength chromium molybdenum steel (34CRM04) alloy is the liner’s material.
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