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DISMANTLING OF ABOVEGROUND LNG STORAGE TANKS
AND THEIR AGING RESEARCH
Hiroshi Nishigami
Maki Yamashita
Shunsuke Ohnishi
Nobuhiro Wadama
Osaka Gas Co., Ltd
Hiroto Yamaoka
Tatsuo Tsuji, Yu Murakami
IHI Corporation
Takehiro Inoue
Naoki Saito
Motohiro Okushima
Nippon Steel & Sumitomo Metal Co., Ltd
KEYWORDS: aboveground LNG storage tank, aging research, dismantling method]
ABSTRACT
In 2011, Osaka Gas commenced the dismantlement of two aboveground LNG storage tanks with a storage
capacity of 45,000 m3 each at the Senboku 1 terminal. The said LNG storage tanks had been in commercial
operation for approximately 40 years, and were the first to be dismantled in Japan. Concurrent with the
dismantlement of the said LNG storage tanks, Osaka Gas also began the research on the deterioration due to
their aging. Aging evaluation of the said LNG storage tanks will contribute to the LNG industry by not only
potentially increasing its lifetime, but by improving its functions and safety as well. In this paper, the method of
dismantling and the research results with regard to the aging for the two types of LNG storage tanks,
respectively made of 9% Nickel steel and Aluminum alloy are reported. The contents of the research will be of
the following criteria: (1) Mechanical properties of 9%Ni steel and Aluminum alloy (2) Thickness of steel pipe
piles (3) Deterioration of instrument devices (4) Deterioration of insulation materials. After dismantling of the
said LNG storage tanks, Osaka Gas decided to construct a large scale LNG storage tank applying newly
developed 7% Ni-TMCP steel for its inner tank. The storage capacity of the new LNG storage tank will be
230,000m3, and is scheduled to be completed by November, 2015. The present state of the construction of the
innovative LNG storage tank will be reported in this paper as well.
1. INTRODUCTION
In 1972, IHI Corporation (IHI) built three LNG storage tanks
with capacities of 45,000m3in Osaka Gas Co., Ltd (Osaka Gas)
Senboku I Terminal. Since then, the tanks, which were of the
single containment type with double steel walls, had been
successfully operated without any trouble for 40 years. However,
the conventional LNG storage tanks were getting more
inefficient in the use of receiving terminal because of its lower
dike in comparison with the state-of-the-art full-containment
LNG storage tanks. (Figure1)
Figure 1. One of the demolished
LNG storage tanks
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To keep up with the increasing demand for LNG and for effective practical use, Osaka Gas started to demolish
the two conventional LNG storage tanks in 2011, and now a large LNG storage tank of 230,000m3has been
under construction since September 2012.
Demolition of old LNG storage tanks was executed with paying sufficient attention to the safety in consideration
of the influences on the other facilities in operation and neighboring companies. Then, Osaka Gas investigated
the demolished LNG inner tanks material and its thermal insulation material jointly with IHI as the constructor
and Nippon Steel & Sumitomo Metal Co., LTD (NSSMC) as the supplier of tanks steel products. Moreover, we
examined the steel pipe piles and the instrumentation devices from Osaka Gass own point of view. This paper
describes the study on dismantling method of LNG storage tanks, the results of the investigations, and also
reports on the new material used for the LNG storage tank under construction.
Investigation items:
1) Base metal mechanical properties (chemical composition / macro-micro structure / tensile strength /
Charpy absorbed energy / retained austenite)
2) Weld metal mechanical properties (chemical composition / macro-micro structure / tensile strength /Charpy absorbed energy)
3) Fracture toughness properties (CTOD test / duplex ESSO test / wide plate test)
4) Corrosion of foundation piles (steel pipe piles)
5) Deterioration of concrete
6) Deterioration of instrumentation devices
7) Deterioration of thermal insulation material
2. DISMANTLING METHOD OF THE LNG STORAGE TANKS
2.1 Specification of the tanks
Table 2.1 and Figure 2.1 show the specifications of the two demolished tanks.
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Table 2.1 Specification of the tanks
1 Internal liquid LNG
2 Capacity 45,000KL
3 Type single containment type with double steel walls
4
Dimensions inner tank outer tank
Diameter 44,600mm 46,400mm
Height 28,820mm 31,850mm
Roof radius 35,700mm 36,600mm
5 Design temp. -162 ambient temp.
6 Design pressure 0.12kg/cm2 50mmH2O
7 Main material 9%Ni steel(Al alloy) carbon steel
8 Insulation perlite & perlite concrete
9 Thickness of insulation
tank shell & roof; 900mm
tank bottom ;1,100mm
10 Foundation slabreinforced concrete
diameter :44,600mm thickness ;800mm
11 Dike
reinforced concrete
height :4,000mm(3,000mm from the ground)
thickness ; 1,400mm
12 Earthquake historyground surface acceleration;
178gal
13 Commercial operation Feb.1972.
Note; ( ) shows Al alloy tank
Figure 2.1 Configuration of the demolished LNG storage tank
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2.2 Dismantling procedure
The LNG tanks were demolished through the following procedure in Figure 2.2.
Step 2 Perlite extraction from the annular space Step 4 Removal of the outer tank roof
Step 6 Removal of the outer tank shell plate Step 7 Removal of the inner tank shell plate
Figure 2.2. Dismantling procedure
(1) Since the tank structure changes at every step during the tank dismantling, the dismantling steps should
be observed by FEM analysis, ABAQUS. Figure2.3 shows some examples of the results by the analysis.
(2) The tanks were dismantled by 150 tons cranes.
(3) Perlite was removed by a new extraction machine.
(4) Some samples for the study were taken before the tank dismantling.
1. Setting of entering road into the dike
2. Perlite extraction from the annular space
3. Removal of the pipe, pipe frame etc.
4. Removal of the outer tank roof
5. Removal of the inner tank roof
6. Removal of the outer tank shell plate
7. Removal of the inner tank shell plate
8. Removal of the outer tank bottom plate
& bottom insulation
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Figure 2.3. The examples ofthe strain diagram
3. INSPECTION AND TEST RESULTS
3.1 Visual inspection
3.1.1 Inner tank
K11 tank (9% Ni steel) and K31 tank (AL alloy) were found to be in good condition. No damages and buckling
were detected due to the Hanshin Awaji Great Earthquake in 1995. There was no influence on the soundness
of the tank. There was no damage to the instrumentation devices (level gauge, thermometer) installed in the
tanks.
3.1.2 Outer tank(a) Manhole for perlite filling
Some corrosion was found at the blind flange of perlite manhole. The doubling plate and the root of the
manhole were also corroded.
(b) Outer tank roof plate and shell plate
Some corrosion was seen at the welding seam. It is estimated that the repair painting had not been done
enough.
(c) Roof walkway
Corrosion was seen just right under the protecting seal due to the deterioration of it. In addition, corrosion was
found at checker plate of walkway.
(d) Anchor bolt
Some anchor bolts especially under the pipe rack were corroded. After removing a weather seal, the surface of
several bolts were corroded and decreased its thickness.
(e) Inner tank anchor strap
As a result of the investigation, the conspicuous deterioration, damage, deformation and corrosion were not
seen. The reason of these phenomena was that the annular space had been filled with nitrogen since the time
of the construction.
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3.2.1 Base Metal of Inner Tank
Table 3.1 shows sampling parts and investigation items of each tank. Details are given as follows.
Table 3.1. Sampling Parts and Tests (Base Metal)
Tank Sampling Part
Chemical
Component
Analysis
Tensile TestCharpy
Impact TestCTOD Test
Duplex
Esso
Test
K31
(A5083)
1st Course - - -
13th Course - - -
Annular Plate - - - -
Bottom Plate - - - -
K11
(9%Ni-Steel)
1st Course
13th Course - -
Annular Plate - - - -
Bottom Plate - - - -
(a) Chemical Compositions of Base Metal
Chemical analyses were carried out on representative samples taken from the 1st and 13th shell courses andannular bottom plate of each tank. Table 3.2 shows the results of K31 tank (made by aluminum alloy), and
Table 3.3 shows that of K11 tank (made by 9%Ni steel).
Table 3.2. Chemical Composition (A5083 Base Metal)
Sampling
PartSi Fe Cu Mn Mg Zn Cr Ti B
Shell Plate
1st Course0.08 0.10 0.01 0.67 4.51
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(b) Tensile Properties
Tensile tests were carried out by using specimens: a full thickness specimen in accordance with JIS Z 2201
No.1A. The tests were performed in both the L and C rolling directions at room temperature in accordance with
JIS Z 2241.
Table 3.4 shows the results of K31 tank, and Table3.5 shows that of K11 tank.
Table 3.4. Results of Tensile Test (A5083-O Base Metal)
Sampling PartRolling
Direction
0.2% Proof
Stress [MPa]
Tensile
Stress [MPa]
Elongation
[%]
Shell Plate
1st Course
L 136 297 23
C 139 303 24
Shell Plate
13th Course
L 153 304 20
C 139 302 21
Bottom PlateL 160 299 18
C 139 303 22
Requirement1)
-125 (0.8
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Figure 3.1. Results of Charpy Impact Test (9%Ni-Steel Base Metal)
Test Temperature:-196
(d) Other
For the 1st shell courses of K11 tank, CTOD test and duplex Esso test were carried out and we make sure of
the soundness of material used in the construction days. The details are omitted due to space limitation.
3.2.2 Weld Joint of Inner Tank
Table 3.6 shows sampling parts and investigation items of each tank. Details are given as follows. Table 3.7
shows the welding procedure of each weld joint. Table 3.8 shows the pictures of macro structure of vertical
weld joint of shell plate 1st course.
Table 3.6. Sampling Parts and Tests (Weld Joint)
Tank Sampling Part Weld Joint
Chemical
Component
Analysis
Tensile
Test
Charpy
Impact TestCTOD Test
Wide Plate
Test
Bending
Fatigue
Test
K31
(A5083)
1st Course Vertical - - - -
1st&2nd Course Horizontal - - - -
13th Course Vertical - - - -
Annular Plate Fillet - - - -
K11
(9%Ni-Steel)
1st Course Vertical -
1st&2nd Course Horizontal - -
13th Course Vertical - - -
Annular Plate Fillet - - - -
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Table 3.7. Welding Procedure of Each Weld Joint
Sampling PartK31 (Aluminum) K11 (9%Ni-Steel)
Process Material Groove Process Material Groove
Shell Plate 1st Course
Vertical Weld JointLarge
Current
MIG
JIS Z 3232
A5183-WY
(AWS 5.10
ER5183)
SMAW
JIS Z 3224
ENi 6133
(AWS 5.11
ENiCrFe-2)
Shell Plate 1st&2nd
Course
Horizontal Weld Joint
Shell Plate 13th Course
Vertical Weld Joint
MIG
Shell Plate 1st Course
& Annular Plate
Fillet Weld Joint
Bottom Plate
One Side
Lap Weld Joint
Table 3.8. Macro Structure of Vertical Weld Joint of Shell Plate 1st Course
K31
Aluminum Tank
K11
9%Ni-Steel Tank
(a) Chemical composition of weld metal
Chemical analyses were carried out on representative samples taken from the different parts of weld metal.
Table 3.9 shows the results of weld metal of K31 tank, and Table 3.10 shows that of K11 tank.
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Table 3.9. Chemical Composition (K31 Aluminum Tank Weld Metal)
Sampling Part Si Fe Cu Mn Mg Zn Cr Ti B
Shell Plate 1st Course
Vertical Weld Joint0.08 0.10 0.01 0.67 4.51
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Table 3.12. Results of Tensile Test (K11 9%Ni-Steel Tank Weld Metal)
Sampling Part
Test after DismantlingConstruction
Management Test
Tensile
Stress [MPa]
Fracture
Location
Tensile
Stress [MPa]
Shell Plate 1st Course
Vertical Welded Joint756 Weld Metal 761
Shell Plate 1st&2nd Course
Horizontal Weld Joint756 Base Metal 767
Shell Plate 13th Course
Vertical Welded Joint781 Base Metal 788
Requirement1)
655 (at 20 deg C) - -
[K31]
These results on tensile strength at room temperature satisfy the requirements1)
, and fracture locations are not
particular. It is apparent that soundness of tank was kept.
[K11]
The same as K31 tank, all results satisfy the requirements1)
, it is apparent that soundness of tank was kept.
(c) Charpy Impact Properties
Charpy impact tests were carried out on weld joints of K11 tank, machining the notch at center of weld metal,
fusion line (FL: 50% weld metal + 50% heat affected zone), FL+1mm, FL+3mm, FL+5mm, using specimens in
accordance with JIS Z 2202 and 3128. Notch is 2mm depth, V shape. The central axis of the specimen was the
same as base metal. The tests were carried out at -196 deg C in accordance with JIS Z 2242.
Figure 3.2 shows the results of Charpy impact tests. All plates conform to the requirements1)
. Those
results have indicated that the weld joints dont deteriorate with age.
Figure 3.2. Results of Charpy Impact Test (K11 9%Ni-Steel Tank Welded Joint)
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(d) Other
For the vertical weld joint of 1st shell courses of K11 tank, CTOD test and wide plate test were carried out and
we make sure of the soundness of welded joints. The details are omitted due to space limitation.
3.3 Corrosion survey on corrosion of foundation piles
3.3.1 Purpose and method
Corrosion countermeasure for foundation piles is important for maintenance of LNG tank substructure. Osaka
Gas adopts a corrosion allowance by adding 2mm margin to the specification of foundation piles in
construction design as a corrosion countermeasure. Meanwhile, heads of piles are bonded in advance during
construction so that a cathodic protection can be applied in preparation for significant corrosion progression in
service. Moreover, the installation method of electrodes using a horizontal boring technique for cathodic
protection has been developed, and the corrosion condition has been monitored in order to judge the necessity
of cathodic protection.
The corrosion condition has been judged according to the thickness measurement which is executed by
remote field testing and actual pile investigation by excavating the upper portion of piles. Based on the
evaluation in this way indicated that there was no necessity of corrosion countermeasure for the next 50 years
at least. Because actual measurement data is still not enough, we conducted a survey on actual piles that
pulled out on this occasion of tank demolition in order to make up for scant data of actual corrosion condition.
Figure 3.3 shows the section view of the LNG tank. There were 496 foundation piles in total that driven with
steel pipe piles; length 25m, outer diameter 406.4mm, thickness of upper pile 12.7mm and lower pile 9.5mm.
As shown in Figure 3.4, the survey was conducted with 31 piles among all foundation ones of LNG storage
tank. The thickness of pile was measured down to 6m below pile head, where the lateral bearing force is
susceptible due to corrosion. In addition, 5 piles among them were measured over the entire length of pile.
The measurement of thickness was carried out after removing extraneous matters such as corrosion products
and residual material. Then the averages of pile thickness were calculated from measured thickness and
weight for each 1m.
Also note that the cathodic protection of impressed current method had been applied to the removed tank from
one year after start-up.
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Figure 3.3. Specification of tank foundation
Figure 3.4. Framing plan of piles and the measured piles in corrosion survey
3.3.2 Result
Observing the appearance of piles, corrosion is found on the outside surface evenly, where local corrosion of
particular part is not found, nor rust inside of the steel pipe. Therefore, the corrosion content is estimated from
the outer wall of a pile by reducing the measured value from the initial thickness of a pile. Figure3.5 shows the
corrosion content according to the depth. The corrosion content is about 0.6mm at a maximum, so it is kept
within 2.0mm margin. Also, no specific difference is found in the corrosion conditions between each depth.
The averaged corrosion rate is obtained as 0.014mm/year at a maximum. It also stays within the confines of
normal corrosion rate that reported various research literatures. The evaluation criterion is estimated at up to
0.073mm/year before this corrosion survey; the total corrosion rating was calculated from adding
0.042mm/year as macro-cell corrosion rate of steel in concrete to 0.031mm/year as maximum natural
corrosion rate. However, the corrosion rate obtained from this survey resulted in far below the conventional
value we estimated.
From pile head to 6m below
Whole length
(Measurement range)
Steel pipe pile
Length: 25.0m
Outer diameter: 406.4mm
Thickness: (Upper part) 12.7mm
(Lower part) 9.5mm
Number: 496
Diameter of base slab: 48.0m
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The effective range of cathodic protection related to the arrangement of foundation piles could not be
ascertained because there was no specific difference found between the outer and the center piles due to the
too small corrosion content.
3.4 Deterioration survey for concrete
3.4.1 Purpose and scope
Diagnostic evaluation for concrete structure used for 40 years was undertaken based on chloride ion content,
carbonation depth and compressive strength of concrete used for the base slab and dike of LNG storage tank.
Measure points are selected at the marked point in Figure 3.6; 5 points on underside of base slab, 4 points on
side surface of base slab, each 4points on outer and inner side of dike.
Figure 3.6. Measure points for concrete deterioration survey
Depth(m)
Corrosion allowance
Corrosion content (mm)
Figure 3.5. Corrosion content
Underside of base slab
Side surface of base slab Outer and inner side of dike
*Only from K031LNGtank on east side.
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3.4.2 Result
(a) Chloride ion content
Chloride ion content as measured at each 20cm depth for 7 measuring points at t underside of base slab and
for 5 measuring points at each side surface of foundation slab and dike. Figure 3.7 shows the chloride ion
content. The covering depth of base slab and dike is 85~105mm, and the chloride ion content at the reinforcing
steels was lower than 2.5kg/m3that specified as criteria of corrosion durability. Also, it shows that almost no
chloride ion content made inroad into the underside of base slab.
(b) Carbonation depth
Figure 3.8 shows the measurement result of carbonation depth. Almost no carbonation progress is found at
base slab. Even the carbonation found at side surface of base slab and dike wall are 25mm at a maximum, it
shows that the carbonation depth does not reach to the reinforcing steels.
Carbonation depth
(mm)
Underside
of base slab
Side surface
of base slabDike
Figure 3.8. Carbonation depth
Minimum covering depth
Chloride ion content
(kg/m3
)
Depth from concrete surface (cm)
Underside of base slab
Side surface of base slab
Dike
Figure 3.7. Chloride ion content
Criteria of corrosion durability
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(c) Compressive strength
Figure 3.9 shows the measurement result of compressive strength. The survey of compressive strength shows
that all the specimens satisfy the design compressive strength of 24.0N/mm2.
3.5 Deterioration of Instrumentation Devices
The following are the report of deterioration investigation of instrumentation devices. The devices below are
selected as objectives for investigation among the instrumentation devices mounted on the tank.
Thermometer for Roll-over detection Guide wire for Float Type Level Meter
These devices have not renewed since the construction of the tanks, and they have been in service without
any failure. However, major renovation work including hot-up and opening of LNG tank would be necessary if
these devices had failure and needed to be repaired. Also, operation of the entire LNG terminal might be
interrupted. Therefore, it is important to investigate the deterioration of these devices for better approach to
future construction and maintenance of LNG tanks.
3.5.1 Thermometer for Roll-over
(a) Outline of Thermometer for Roll-overHere is the detail of Thermometer for Roll-over.
This thermometer has a very important role in monitoring LNG stratification that is considered as a warning
symptom of roll-over phenomenon.
As shown in Figure 3.10, 15 thermometers are arranged at intervals of 2m from the top of LNG tank.
According to the indicated values of the thermometers, supervised computer system (hereafter SCS) judges
the occurrence of LNG stratification. When SCS detects stratification, it sends an alert signal to the center
control room (hereafter CCR) and requires the operator to take measures, such as sending out, transfer or
circulation.
Compressive strength
(N/mm2)
Underside
of base slab
Side surface
of base slabDike
Figure 3.9. Compressive strength
Design compressive strength
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Figure 3.11. Insulation
resistance test
Figure 3.10. Arranged thermometers
(b) Objective for Investigation
30 thermometers for roll-over taken from the two removed LNG tanks are used for investigation.
The specifications of the thermometer are described below:
Model : Metal-sheathed resistance thermometer sensor
Sheath material : SUS316
Sheath outer diameter : 4.8mm
Sheath length : 13m~41m (at intervals of 2m)
Classification : 0.5
Detection element : Platinum resistor
(Standard resistance value : Pt100at 0 (JPt100))
Conductor : 3-wire type
(c) Investigation Contents / Method
It has already reported that there are some thermometers indicating the
signs of insulation degradation before the LNG tanks removal. If the
insulation degradation occurred, the ability of measuring temperature
deteriorated. Furthermore, if the insulation completely damaged,
temperature measurement became impossible subsequently. Prior to the
investigation, we implemented insulation resistance test (applied voltage:
100CV) for all thermometers just before removing them to identify the
thermometers having the insulation degradation. Then we cut off the
sheath off from the head of the thermometer having insulation degradation
and implemented insulation resistance test (Figure 3.11) again to investigate
the region where insulation degradation occurred.
(d) Result of Investigation
Table 3.13 shows the result of the insulation resistance test. There were 5 thermometers that had lower
insulation resistance value than 20M at the time of measurement before removing. However these
thermometers had more than 20Mof insulation resistance in the second test after cutting the sheath for 1m
off from the head. Therefore, it can be said that insulation degradation of the thermometers occurred within1m from the head.
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Table 3.13. The result of insulation resistance test and region of insulation degradation
Thermometer No.Insulation resistance
[M]
Region of insulation
degradation [m]
(distance from the head)
No.1 LNG tank
1 1 13 6 1
5 2 1
12 11 1
No.3LNG tank 1 0.1 1
(e) Conclusion
The insulation degradation was found on 5 thermometers among all 30 objective thermometers. However,
they did not have severe degradation to the extent of influencing the measuring ability of thermometers. The
degradation occurred within 1m from the thermometers head according to the investigation of region. It is
assumed that the cause of insulation degradation was the influent water from the terminal area covered with
epoxide resin. The epoxide resin used for insulating the terminal area had deteriorated.
The insulation degradation was solved by cutting off the deteriorated region in upper 1m. We conclude that
the thermometer should be installed with extra length to deal with insulation degradation.
3.5.2 Guide wire for Float type level meter
(a) Outline of Float type level meter
Here is the detail of Float type level meter.
Figure 3.12 shows the float type level meter removed from the tank on this occasion. It is used to measure the
liquid level according to the length of the tape that goes up and down depending on the float on the liquid
surface. The float moves along the guide wires. Therefore, friction arises between the float and the guide
wires every time when the float moves. In this investigation, the deterioration condition of guide wires were
inspected for taking into account the risk of broken guide wires.
Figure 3.12. Float type level meter
(b) Objective for investigation
There were 2 floating type level meter mounted on each removed LNG tank. One of the guide wires on eachLNG tank was selected as objectives. Specification of the guide wire is described below.
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Applied standard : JIS G 3550
Material : SUS304
Product name : Independent strand core rope
Constructive number : 719
Length : approx. 37.5m
Diameter of wire : 10mm
Diameter of strand : 0.67mm
(c) Investigation Contents / Method
We supposed that the worn volumes were different depending on the positions of a guide wire in
consideration of normal liquid level; too high and too low level were less frequent. Therefore, the samples for
investigation were picked up for each 1000mm from three positions, upper, middle and lower part. Table 3.14
shows the details of samples. Then we made a comparison of deterioration degree of these guide wires.
Table 3.14. Details of samples
Distance from the bottom of
tank [m]
Total times of
round-trip [time]*
Sample 1 (upper) 33 0
Sample 2 (middle) 17 1,000
Sample 3 (lower) 6 200
* Total times of round-trip after the installation are estimated from liquid level change for a year in 2010.
1) Observation of appearance / gauging of diameter
We inspected the worn volume of sampled wires and their strands by visual and a digital microscope.
Also, we gauged the diameters of each sample to compare the values to the standard criterion of JIS
and among the samples obtained from each position.
2) Tensile test
We implemented tensile test of sample wires if these wires satisfy the breaking force specified in JIS G
3550; for tensile test, both edges of wires were bonded by white metal.
We picked up 1 strand of each 6 strand excluding the core as objectives for tensile test of wire, and
implemented tensile test if these wires satisfied the breaking force specified in JIS G 4314 under the
condition; length of specimen between grips100mm, tension rate 50mm/min.
(d) Result of inspection
1) Observation of appearance / gauging of diameter
Figure 3.13 shows the pictures of wires appearance and their diameters. There was no thinner wire
than 10mm (the criterion specified in JIS G 3550) and no difference was found among each position.
Red rust was found on some wires however it could be wiped off easily (it is supposed that this red rust
adhered at the removing work).
Figure 3.14 shows the pictures of strands appearance and their diameters observed by a digital
microscope. There were small wears found at the parts marked with red arrows. However these wears
were not serious and the wires had enough diameters over the 0.67mm of regulation size. It can besaid that there was no wear on the wires.
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Figure 3.13. Wires diameters Figure 3.14. Strands diameters
2) Tensile test
Table 3.15 shows the result of tensile test for wires. All wires at each position satisfy the level of
standard breaking force 61.8kN for 10mm wire. Also, no difference was found among each position.
Therefore, it can be said that there was no deterioration of wires.
Table 3.16 shows the result of tensile test for strands. Some strands of No.3 LNG tank exceeded over
the maximum level of standard breaking force 1850~2100MPa for 0.67mm wire. However, no strands
exceeded the minimum level and no difference was found among each position. Therefore, it can be
said that there was no deterioration of strands.
Table 3.15. The result of tensile test for wires
Standard breaking
force of wire [kN]
Breaking force of wire [kN]
No.1 LNG tank No.3 LNG tank
Upper
61.8
64.0 68.2
Middle 64.8 71.4
Lower 66.8 72.2
Table 3.16. The result of tensile test for strands
Breaking force of strand [MPa]Standard breaking
force of strand [MPa]No.1 LNG tank No.3 LNG tank
Upper Middle Lower Upper Middle Lower
1 2037 2036 2009 2102 2179 2169
1850~2100
2 2030 1996 2044 2089 2185 2094
3 2100 1962 2052 2089 2127 2149
4 1996 2000 2016 2169 2146 21635 2038 1978 2036 2137 2194 2135
6 2056 1989 1990 2143 2165 2114
Average 2043 1994 2025 2121 2166 2137
(e) Conclusion
We investigated the deterioration condition of guide wires for Float type level meter that had been installed in
two LNG tanks. The guide wires have no specific wear and satisfy the standard specifications for both
diameter and breaking force. We conclude that the guide wires for Float type level meter have enough
properties that allow continuous use for 40 years.
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3.6 Thermal insulation material
The following thermal insulation materials (i.e. perlite, Mesalite (Mitsui Expanded Shell Light-Weight
Aggregate) concrete, perlite concrete block and cylindrical perlite concrete) were investigated (Figure.3.15).
Figure 3.15. Structural drawing of thermal insulation
3.6.1 Perlite
Perlite was sampled from the top, the middle, and the bottom of annular space, and also from inside of the
cylindrical concrete.
(a) Thermal conductivity
Thermal conductivities were measured under the temperature condition of 3 steps(-20~30, 5~35, 20~50
). We calculated these values by using the regression equation and obtained the thermal conductivities at
the zero Celsius degree. Thermal conductivities of each sample of perlite satisfy the specifications at the time
of the construction.
Table 3.17. Thermal conductivity of perlite
Sample LocationThermal conductivity(T.C.)
W/mK)(at 0Ratio
*1
Top of annular space 0.0433 0.98
Middle of annular space 0.0429 0.97
Bottom of annular space 0.0391 0.88
In cylindrical perlite concrete 0.0399 0.90
specification 0.0442 1.00
note;*1:The ratio of the measured values to the specification value
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3.6.2 Mesalite concrete
(a) Compressive strength
The test was carried out in accordance with JIS A1108 (this standard follows ISO 1920-4). The test results are
shown in Table 3.18. Compressive strength of the samples satisfies the specification value at the time of the
construction. The specific gravity was almost the same as the value at the time of the construction.
Table 3.18. Compressive strength of Mesalite concrete
specification (N/cm2) Test result (N/cm
2) Ratio
*1
1470 1955 1.33
note;*1: The ratio of the measured values to the specification value
(b) Thermal conductivity
The test was carried out in accordance with ISO 8301(Heat Flow meter apparatus Method). Thermal
conductivity was calculated at zero Celsius degree by the equation regression as same as perlite. The test
result value shown in Table 3.19 was less for approximately 67% than the construction specification and was agood value.
Table 3.19. Thermal conductivity of Mesalite concrete
Specification (W/mK) Test result (W/mK) Ratio*1
0.93 0.309 0.33
note;*1: The ratio of the measured values to the specification value
The properties of Mesalite concrete have not been changed since the days of construction.
3.6.3 Perlite concrete
(a) Thermal conductivity
The test was carried out in accordance with ISO 8301(Heat Flow meter apparatus Method).The test result
value shown in Table3.20 was less for approximately 14% than construction specification and was a good
value.
Table 3.20. Thermal conductivity of perlite concrete
Specification (W/mK) Test result (W/mK) Ratio*1
0.1163 0.10028 0.86
note;*1: The ratio of the measured values to the specification value
3.6.4 Cylindrical perlite concrete
(a) Thermal conductivity
The test was carried out in accordance with ISO 8301(Heat Flow meter apparatus Method). The test result
value shown in Table 3.21 was less for approximately 7% than construction specification and was a good
value.
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Table 3.21. Thermal conductivity of Cylindrical perlite concrete
Specification (W/mK) Test result (W/mK) Ratio*1
0.1163 0.10782 0.93
note;*1: The ratio of the measured values to the specification value
4. PRESENT SITUATION OF THE TANKS UNDER CONSTRUCTION
The inner tank material for above ground LNG storage tanks has mostly been made of 9% Ni steel plate over
the 50 years as it has excellent mechanical properties under -160deg.C. During this period, the LNG storage
tanks made of 9%Ni steel plate have safety operated. It is known that 9%Ni steel has excellent cryogenic
fracture toughness due to the retained austenite and refinement microstructure obtained by nickel content and
heat treatment process.
NSSMC, Toyo Kanetsu K.K (TKK) and Osaka Gas jointly developed 7%Ni-TMCP steel having the comparable
performance to 9%Ni steel. Newly developed 7%Ni-TMCP is achieved 2% reduction of nickel content from the
conventional 9%Ni steel by adopting Thermo Mechanical Control Process (TMCP). Various basic performance
tests and fracture toughness tests in development process showed that the base metal and welded joints
satisfy the regulatory and technical requirements for LNG storage tanks. In 2010, Japanese Ministry of
Economy, Trade and Industry (METI) approved the use of 7%Ni-TMCP steel for newly-built tank of Osaka Gas.
The development of 7%Ni-TMCP steel realizes the reduction of rare metal nickel to be used. Therefore, not
only the cost of inner tanks material but also the cost of nickel in rising market can be saved.
From September 2012, Osaka Gas started the construction of 230,000m3full-containment tank in Senboku I
Terminal. Installation of steel pipe piles had been done at the time of October 2012 and the base slab is now
under construction (Figure4). The construction of the tank will be completed by November 2015.
Figure 4. The picture of present situation at construction area
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5. CONCLUSION
Osaka Gas demolished the two LNG storage tanks that had actually been used for about 40 years. On this
occasion, we assured the secure dismantling method and verified that the mechanical properties (including
chemical composition, tensile strength and Charpy absorbed energy) of 9%Ni steel and Al alloy used as inner
tanks material satisfied sufficient levels. Thermal insulation material, steel pipe piles and instrumentation
devices have no significant deterioration. These investigations proved the high integrity of the LNG storagetanks.
The results of these investigations obtained from the demolished LNG storage tanks that had been used for
about 40 years provide invaluable actual data and it contributes to the progress of LNG storage tank market in
the future.
REFERENCE
1) Recommended Practice for LNG Aboveground Storage; Japan Gas Association 2012