1. Yohsuke Tamura, Koji Yamazaki, Kiyotaka Maeda and Kenji Sato
INTERNATIONAL CONFERENCE ON HYDROGEN SAFETY
September, Hamburg (Germany)
ID 104
The residual strength of automotive hydrogen cylinders after exposure to flames
Yohsuke Tamura, Koji Yamazaki, Kiyotaka Maeda　and Kenji Sato
（JARI，Toho Univ.)

2. Contents Back ground and purpose Structure of cylinder
Safety requirement for the handing of cylinder exposed to fire
Test method and test condition
Results
Temperature and Internal pressure during fire
Appearance of cylinders after exposure to flames
The residual strength of cylinders after exposure to flames
Consideration
Summary

3. Structure and type of automotive CFRP cylinders
TPRD
Type Ⅲ： aluminum alloy
Type Ⅳ： plastic
Liner
　　CFRP
Carbon fiber
Matrix resin

4. About TPRD (Thermal Pressure Relief Device)
Gas
CFRP　cylinder
To prevent the rupture of the cylinder, TPRD attached on the CFRP composite cylinder, was activated by the heat of fire.

5. Safety requirement for the handing of cylinder exposed to fire
TPRD
CFRP cylinder
When the fire is extinguished before TPRD is activated, the high-pressure gas is left inside the cylinder damaged by fire. For the safe handling of such a cylinder, it is necessary that despite damage by fire the cylinder retain sufficient strength for withstanding the internal gas pressure.

6. In this study
Using the cylinder without the TPRD in order to assuming the worst condition that the TPRD did not activate, residual strengths of the cylinders after burning that overheated to just before rupture or leakage were examined.

7. Test method Rupture conditions at a constant buring fire
Pressure
Temp.
Rupture conditions at a constant buring fire
(temperature, pressure, time, etc.)
Water
Pressure
Temp.
Natural cooling
Hydraulic burst test
Sample cylinders cut off the fire source and cooling (water or natural cooling) just before rupture. These cylinders examine the bursting pressure by the hydraulic burst test.

8. Test condition
Test cylinder：
　Total of five types (20~70MPa　Type Ⅲ, Type Ⅳ)
Filling pressure :
　Workling pressure、 Half of the working pressure

9. Fire exposure conditions
　Burner Measure point of temp. .
　Firepower is controlled to 600~800 °C　at 25mm from the cylinder bottom
　Engulfing fire、Localized fire exposured a half of the cylinder

10. Result -Flame and cylinder temp., Internal pressure

11. Result -Flame and cylinder temp., Internal pressure

12. Result -Flame and cylinder temp., Internal pressure

13. Internal pressure during fire expose and cooling
Burst pressure during fire
Case: 70MPa TypeⅣ cylinder, Filling 70MPa, Engulfing fire
Supply of heat per unit time was the same condition.
These had provided the cylinders with the maximum possible exposure to flames.

14. Situation of flame expose test
35MPa TypeⅢ　Natural cooling　

15. The appearance of a cylinder after exposure to flames
Case: 35MPa TypeⅢ cylinder, Filling 35MPa, Engulfing fire
Water cooling
Natural　cooling

16. Hydraulic burst test

17. Burst pressure after extinguishment of a fire
Cylinder
Flame exposure conditions
Filling pressure
Cooling condition
Burst pressure　after extinguishment of a fire
Burst pressure/　Filling pressure
Burst pressure/　Burst pressure of new cylinder
20MPa TypeⅢ
Engulfing fire
20MPa
Water　cooling
more 84.2MPa
more 4.21
0.92
Natural cooling
more 84.7MPa
more 4.24
Localized fire
Water cooling
82.7MPa
4.14
0.89
25MPa TypeⅣ
25MPa
77.5MPa
3.1
0.63
79.8MPa
3.19
0.65
35MPa TypeⅢ
35MPa
111.1MPa
3.17
0.90
73.3MPa
2.09
0.60
70MPa TypeⅣ
70MPa
188.4MPa
2.69
1.00
187.9MPa
2.68
173.4MPa
4.95
0.94
TypeⅢ
197.5MPa
2.82
0.87
193.0MPa
5.51
0.85

18. Extinguished after the CFRP layer after extinguishment of a fire
Layer of outside side were damaged by heat decomposition of matrix resin.

19. Heat characteristics of CFRP
Strength during heating (fire) is reduced more than the glass transition temperature Tg.
Strength after cooling (extinguished) is restored less than the heating resin loss start temperature Te.
Tg<Te
Reference : A. P. Mouritz(2006), Atsushi Sumida(2008)

20. Restore strength of CFRP
Image diagram of temperature and stress change in the cylinder after fire during flame exposure
Restore strength of CFRP
Reduction of load accompanying decrease of internal pressure
The strength of the CFRP cylinder after extinguished is higher than that during fire, has the strength to withstand the filling pressure

21. Summary
To examine the handling of the CFRP cylinder after extinguished, CFRP cylinders without pressure relief device were exposed to a fire to the verge of bursting; then after the fire was extinguished the residual burst strengths was examined. The results indicated that these cylinders had a residual strength at least twice their internal gas pressures. Therefore, we consider that the burnout of cylinder will has the strength to withstand the pressure of the filling gas.

22. Thank you for your attention．
This study introduces one of the achievements of the “technology development project for hydrogen production, transport and storage systems” commissioned by New Energy and Industrial Technology Development Organization (NEDO) in Japan.