Experimental Study of Floating Roof Integrity for Seismic Sloshing. October 8, 2008 Haruki NISHI, Dr.Eng.

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1 Experimental Study of Floating Roof Integrity for Seismic Sloshing October 8, 2008 Haruki NISHI, Dr.Eng. National Research Institute of Fire and Disaster Fire and Disaster Management Agency

Background Oil storage tanks are regulated by the Fire Service Law (FSL) in Japan. Technical standards of Earthquake-proof OST are defined in the FSL. the standard in API 650 App. E 20.

2 Background Oil storage tanks are regulated by the Fire Service Law (FSL) in Japan. Technical standards of Earthquake-proof OST are defined in the FSL. the standard in API 650 App. E 20.7% of large earthquakes are occurred in Japan. Six floating roofs sank and two tank fires occurred in the 2003 Tokachi-oki earthquake. Collapse of a floating roof may lead to a large tank fire, FDMA decided to reinforce the standard to prevent a similar disaster in the future earthquake.

3 Distribution of Hypocenter of Large Earthquakes(>M5.0, )

of motion; simple planar, nonplanar, rotational, irregular beating, symmetric, asymmetric.

4 Sloshing Any motion of the free liquid surface inside its containers Depending on the type of disturbance and container shape, the free liquid surface can experience different types of motion; simple planar, nonplanar, rotational, irregular beating, symmetric, asymmetric. Actual FRT has a floating roof on the surface. Floating roof may collapse by the sloshing.

5 Liquid sloshing in cylindrical tank Under sinusoidal lateral excitation, free surface

6 Seismic Sloshing of Oil Storage Tank Resonance between liquid (oil) and ground motion Larger diameter longer sloshing period Higher liquid height shorter sloshing period D=10m T=3s D=50m T=8s D=100m T=13s

Damage to the Oil Storage Tanks due to Liquid

Damage Overflow of the Oil Tank Fire Ring-type,

7 Damage to the Oil Storage Tanks due to Liquid Sloshing in the Past Earthquakes 1964 Niigata Earthquake Nihonkai-chubu Earthqukae(1983) 2003 Tokachi-oki Earthquake 昭和石油新潟製油所 Detail of the Damage Overflow of the Oil Tank Fire Ring-type, Open-top Sinking of the Floating Roof タンクのリング火災 ( 秋田火力発電所 )

8 Ring-type (Rim) fire on crude oil tank ( )

9 Open-top (Full surface) fire on Naphtha tank ( )

Sinking of the floating roof of the 40,000k l kerosene tanks 30063 Naphtha Tank

40062 Kerosene Tank Two floating roofs sank.

10 Sinking of the floating roof of the 40,000k l kerosene tanks Naphtha Tank Naphtha Tank Kerosene Tank Kerosene Tank Kerosene Tank Kerosene Tank Two floating roofs sank. (2003/9/30 16:43) (2003/9/28 14:26) Fractured welding part between the outer rim and the lower deck of the pontoon (Bottom view)

11 Oil spill onto the deck of the 100,000kl crude oil tank(2003/9/26) Buckling of the pontoons Diameter 80m, Estimated sloshing height 1.4m

Floating roof of the #100654 crude oil tank sank

earthquake) Fractured welding Buckled pontoon(p40&p41) of

12 Floating roof of the # crude oil tank sank completely in the end (2003/9/30, four days after the earthquake) Fractured welding Buckled pontoon(p40&p41) of the # crude oil tank (2 nd mode dominant, sloshing height 1.4m)

13 Evaluation method of the Sloshing Height in the Fire Service Law (1) Natural period of the 1 st order mode of sloshing D Ts1 2 coth 3.68g 3.68H D Here, D:Tank diameter, H:Liquid height, g:gravitational acceleration (2)Maximum sloshing height (1) (1) max H D D 2g π T ( 1) 2 max S1 S V (2) Here, Sv:Velocity response spectrum (105cm/s 200cm/s present) Based on the velocity potential theory with small sloshing height assumption

Strength Evaluation of Floating Roofs for Seismic Sloshing Standard before the earthquake in the FSL API650 Appendix C C.3.4.

14 Strength Evaluation of Floating Roofs for Seismic Sloshing Standard before the earthquake in the FSL API650 Appendix C C Floating roofs shall have sufficient buoyancy to remain afloat on liquid a. 250mm of rainfall in a 24-hour b. Two flooded pontoon compartments plus center deck in single-deck pontoon roofs

15 2 Building a structural evaluation system of a floating roof (Problem to build a simpler method) To prevent the same damage in the future earthquake from occurring Problem (1)Linear response could not explain the damaged to the floating roof (2) Floating roof of the 100,000kl tank damaged even with small sloshing height (1) Effect of the 1 st mode 40,000kl 4m 1 0 (Simplification) Effect of the Large sloshing height and non-linear sloshing Velocity response spectrum & damping factor (2) Effect of the 2 nd mode 100,000kl Evaluation of the effect of the out of plane deformation of the deck Construct technical standards regarding a structural evaluation in the Fire Service Law 石油タンクは消防法で規制現行では雨水滞水時の浮力に関する規定があるだけ

16 Normal Sloshing (Elevation angleθ) θ Side view at sloshing(rotate C.C.W.)

17 Model tank experiment using shaking table Capacity Diameter Height Roof type Liquid height Content 300kl 7.6m 5m Single-deck type 3m Water Natural period 1st mode 3(sec) 2nd mode 1.7(sec)

18 Mode Floating Roofs Carbon steel (thickness 4.5mm) Aluminum(thickness3mm) Stainless steel(thickness1mm) Stainless steel(thickness 0.3,0.6mm) D D 4 g R D 10 7

19 Sloshing Experiment of Free Surface

20 1 st mode excitation experiment using the aluminum floating roof

21 Stainless Steel Floating Roof (thickness 0.3mm) Experiment exciting 2 nd mode of Sloshing Central part of the deck of the floating roof vibrates heavily. (Amplitude of shaking table 22mm 20waves period1.7s Sv=2800mm/s)

Floating Roof Shaking Experiment using an Actual Tank Air Cylinder Deck A 38000 A:magnification Shell plate

22 Floating Roof Shaking Experiment using an Actual Tank Air Cylinder Deck A A:magnification Shell plate Pontoon 20 Annular deck 6t 4.5t 4.5t 8t Deck Diagram of the actual tank (capacit 15,000kl)

23 Floating roof excitation equipment Valve Air cylinder Controller Jig Air compressor Shell plate Eight air cylinders are installed onto the floating roof

24 Point of loading Point of loading Restriction Only 1 st mode can be excited since the points of loading are At the pontoon. Inner diameter 250mm Stroke 2m Max. rated pressure 0.7MPa Double acting cylinder Push pull loading

25 D am ping factor(%) Damping Factor and Sloshing Height Sloshing height(m m ) 0.25M Pa_600s 0.2M Pa_600s 0.15M Pa_600s 0.3M Pa_300s 0.25M Pa_300s 0.2M Pa_300s 0.15M Pa_300s 0.1M Pa_300s Relationship between sloshing height and damping factor at each air pressure and excitation duration

26 Measurement of the Circumferential bending strain at the pontoon Shell plate Pontoon Annular deck Strain gauge 歪みゲージ Deck Cross section of the pontoon

B ending strain( st) Verticaldisplacem ent (m m ) Strain Measured at the Pontoon and Calculated Strain from the FSL 40 0 800 0 P ontoon low er end -40-800 P ontoon upper end C al.

27 B ending strain( st) Verticaldisplacem ent (m m ) Strain Measured at the Pontoon and Calculated Strain from the FSL P ontoon low er end P ontoon upper end C al Time Interval s Elapsed tim e(s) η1m ax η (1) max:0.813(m) β 1m : k: (N/m 2 ) E: (N/m 2 ) I θ : (m 4 ) Rm:17.6(m) ρ: (kg/m 3 ) B:2.4(m) M θ : (Nm) Ze: (m 3 ) σ b1 : (N/m 2 ) b1 b1 E 2.26 Z eff 8EI R 4 m k k I R m (1) max R m 2 Strian b1 becomes large when sloshing height η (1) max is both at max. and min.

Conclusions Elucidate the mechanism of damage to large

sloshing height for the 1 st mode and the 2 nd mode

Height Estimation more than 2m 4m (depending the region

9 y Fire Service law and related ordinance were revised

28 Conclusions Elucidate the mechanism of damage to large oil storage tank during an earthquake Regarding large sloshing height for the 1 st mode and the 2 nd mode Reinforcing Seismic Design of Floating Roof Sloshing Height Estimation more than 2m 4m (depending the region and tank diameter) Strain at Pontoon < 0.9 y Fire Service law and related ordinance were revised in 2005 Enforced in 2005 Plan of reinforcement by 2007 Reinforcement by 2017

29 End

30 補強案 A Shell plate Pontoon Annular deck Deck 補強案 B Shell plate Pontoon Annular deck Deck

31 Non-linearity of the sloshing a Non-linear z Linear a Upward: z + =z+a Downward : z - =z-a Shape of wave surface cross section when small sloshing height assumption dose not hold When sloshing height is large, upward height and downward height differ.

32 D isplacem ent(m m ) Wave form for excitation experim e nt Input w ave data Tim e(s) Laser displacement meter Shaking direction Wire displacement meter on the rack

33 Real Sloshing (Non-linear) a a Side view at sloshing(rotate C.C.W.) Out-of-plane bending Fracture of welded part of the pontoon by out-of-plane bending

34 M 1m max 8EI R 4 m k k Strain at the pontoon 1m EI R m (1) max R m 2 Max. circumferential bending moment of the pontoon modeled as a ring beam Ratio of the rigidity of the outer pontoon and the spring corresponding to the buoyancy b1 M Z eff M θ Circumferential bending stress of the pontoon M θ b1 b1 E 2.26 Z eff 8EI R 4 m k k I R m (1) max R m 2

Dynamic Analysis of Large Steel Tanks

Transactions of the 17 th International Conference on Structural Mechanics in Reactor Technology (SMiRT 17) Prague, Czech Republic, August 17 22, 2003 Paper # K14-1 Dynamic Analysis of Large Steel Tanks