experimental study of floating roof integrity for …...floating roof of the #100654 crude oil tank...
TRANSCRIPT
Experimental Study of Floating Roof
Integrity for Seismic Sloshing
October 8, 2008Haruki NISHI, Dr.Eng.
National Research Institute of Fire and DisasterFire 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
20.7% 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.
Distribution of Hypocenter of Large
Earthquakes(>M5.0,1998-2007)
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.
Liquid sloshing in cylindrical tank
Under sinusoidal lateral excitation, free surface
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=10mT=3s
D=50mT=8s
D=100mT=13s
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
Detail of the Damage
• Overflow of the Oil
• Tank Fire Ring-type, Open-top
• Sinking of the Floating Roof
昭和石油新潟製油所
タンクのリング火災(秋田火力発電
所)
Ring-type (Rim) fire on crude oil tank
(2003.9.26)
Open-top (Full surface) fire on Naphtha tank
(2003.9.28)
(2003/9/28 14:26)
Two floating roofs sank. (2003/9/30 16:43)
Sinking of the floating roof of the 40,000k
l kerosene tanks
Fractured welding part between the outer rim and the lower deck of the pontoon(Bottom view)
40062 Kerosene Tank
40061 Kerosene Tank
30063 Naphtha Tank
40062 Kerosene Tank
40061 Kerosene Tank
30063 Naphtha Tank
Oil spill onto the deck of the 100,000kl crude oil
tank(2003/9/26)
Diameter 80m, Estimated sloshing height 1.4m
Buckling of the pontoons
Buckled pontoon(P40&P41) of the #100654 crude oil tank(2nd mode dominant, sloshing height 1.4m)
Fractured welding
Floating roof of the #100654 crude oil tanksank completely in the end(2003/9/30, four days after the earthquake)
D
H
g
DTs
68.3coth
68.321 ・
V
S
S T
π.
g
D
1
max)1( 2
83702
(1) Natural period of the 1st order mode of sloshing
Here, D:Tank diameter, H:Liquid height,
g:gravitational acceleration
(2)Maximum sloshing height
D
H
Here, Sv:Velocity response spectrum (105cm/s→200cm/s present)
(1)
(2)
(1)max
Based on the velocity potential theory with small sloshing height assumption
Evaluation method of the Sloshing Height
in the Fire Service Law
Strength Evaluation of Floating
Roofs for Seismic Sloshing
Standard before the earthquake in the FSL
API650 Appendix C
C.3.4.1
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
Effect of the Large sloshing height and non-linear sloshing
Evaluation of the effect of the out of plane
deformation of the deck
Building a structural evaluation system of a floating roof
(Problem to build a simpler method)
Construct technical standards regarding a structural evaluation
in the Fire Service Law
(Simplification)
(1) Effect of the 1st mode
(2) Effect of the 2nd mode
(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 heightProblem
Velocity response spectrum & damping factor
-2 0 2
-2
0
2
-1
0
1
-2 0 2
-2
0
2
-2 0 2
-2
0
2
-1
-0.5
0
0.5
1
-2 0 2
-2
0
2
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
40,000kl、4m
100,000kl
To prevent the same damage in the future earthquake from occurring
Normal
Sloshing(Elevation angleθ)
Side view at sloshing(rotate C.C.W.)
θ
Model tank experiment using
shaking tableCapacity Diameter Height Roof type Liquid
height
Content
300kl 7.6m 5m Single-deck type 3m Water
Natural period1st mode 3(sec)2nd mode 1.7(sec)
Mode Floating Roofs
Carbon steel (thickness 4.5mm) Aluminum(thickness3mm)
Stainless steel(thickness1mm)Stainless steel(thickness 0.3,0.6mm)
4Rg
DD
710≒D
Sloshing Experiment of Free Surface
1st mode excitation experiment
using the aluminum floating roof
Stainless Steel Floating Roof (thickness 0.3mm)
Experiment exciting 2nd 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
38000
DeckAir Cylinder
A
A:magnificationShell plate
Pontoon× 20 Annular deck
Deck
32500
38000
6t 8t4.5t4.5t
200 2400150
Diagram of the actual tank(capacit 15,000kl)
Floating roof excitation equipment
Eight air cylinders are installed onto the floating roof
Shell plate
Air cylinder
Jig
Air compressor
Controller
Valve
Inner diameter 250mmStroke 2mMax. rated pressure 0.7MPaDouble acting cylinder→
Push pull loading※RestrictionOnly 1st mode can be excited since the points of loading are
At the pontoon.
Point ofloading
Point of loading
Damping Factor and Sloshing Height
0
1
2
3
4
5
6
7
0 500 1000
Sloshing height(m m )
Dam
ping factor(%)
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
Measurement of the Circumferential bending
strain at the pontoon
Cross section of the pontoon
歪みゲージ
Shell plate
Pontoon
Annular deck
Deck
200 2400
Strain gauge
-160
-120
-80
-40
0
40
300 310 320 330 340 350
Elapsed tim e(s)
Ben
ding strain(
st)
-3200
-2400
-1600
-800
0
800
Vertical displace
men
t (m
m)
Pontoonlow er end
Pontoonupperend
C al.
η1m ax
Strain Measured at the Pontoon and Calculated
Strain from the FSL
2)1(
max
4
11
8
26.2
mm
m
eff
bb
RR
I
kR
EI
k
ZE
TimeInterval7.5s
Strian b1 becomes large when sloshing height η(1)max
is both at max. and min.
η(1)max:0.813(m)
β1m:3.23×10-1
k:2.35×104(N/m2)
E:2.06×1011(N/m2)
Iθ:0.00287 (m4)
Rm:17.6(m)
ρ:1.00×103(kg/m3)
B:2.4(m)
Mθ:5.23×104(Nm)
Ze:2.08×10-3(m3)
σb1:2.52×107 (N/m2)
Conclusions
Elucidate the mechanism of damage to large oil storage tank during an earthquake
Regarding large sloshing height for the 1st mode and the 2nd mode
→ Reinforcing Seismic Design of Floating Roof
Sloshing Height Estimationmore 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
End
Shell plate
Pontoon
Annular deck
Deck
Shell plate
Pontoon
Annular deck
Deck
補強案A
補強案B
z
a
a
Linear
Non-linear
Shape of wave surface cross section when smallsloshing height assumption dose not hold
Non-linearity of the sloshing
When sloshing height is large, upward height and downward height differ.
Upward:
z+=z+a
Downward:
z-=z-a
Wire displacement meter on the rack
Shaking direction
Wave form for excitation
-10
-5
0
5
10
0 10 20 30
Tim e(s)
Displacement(mm)
experim ent
Inputw ave data
Laser displacement meter
Real Sloshing(Non-linear)
Out-of-plane bending
Fracture of welded part of the pontoon by out-of-plane bending
a
a
Side view at sloshing(rotate C.C.W.)
Strain at the pontoon 2
)1(
max1max
26.2mm
mRR
EIM
kR
EI
k
m
m
4
18
eff
bZ
M1
Max. circumferential bending moment of the pontoon modeled asa ring beam
Ratio of the rigidity of the outer pontoon and the springcorresponding to the buoyancy
Circumferential bending stress of the pontoon
Mθ
Mθ
2)1(
max
4
11
8
26.2
mm
m
eff
bb
RR
I
kR
EI
k
ZE