LARGEST ABOVEGROUND PC LNG STORAGE TANK IN THE WORLD, INCORPORATING THE LATEST TECHNOLOGY-CONSTRUCTION COST REDUCTION AND SHORTENING OF WORK ...
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LARGEST ABOVEGROUND PC LNG STORAGE TANK IN THE
WORLD, INCORPORATING THE LATEST TECHNOLOGY—
CONSTRUCTION COST REDUCTION AND SHORTENING
OF WORK PERIOD BY EMPLOYING
NEW CONSTRUCTION METHODS
RESERVOIR GNLBP LE PLUS GRAND DANS LE MONDE
REALIZE PAR LA TECHNOLOGIE DE POINTE—
TECHNOLOGIE DE REDUCTION DE COUTS ET DUREE DE
CONSTRUCTION PAR L’IMPLANTATION
DE NOUVELLES METHODES
Takeyoshi Nishizaki, Motohiko Nakatani, Koichi Miyagawa, Naoshige Kubo
Engineering Dept., Osaka Gas Co., Ltd.
1-2, Hiramomachi 4-Chome, Chuo-ku,
Osaka, 541-0046, Japan
Fumio Kamada
Obayashi Corporation
Shinagawa Intercity Tower B 2-15-2, Konan, Minato-ku,
Tokyo, 108-8502, Japan
Minoru Okudate
Obayashi and Konoike J.V.,Obayashi Corporation
4-33, Kitahama-higashi, Chuo-ku,
Osaka, 540-8584, Japan
Kazuyuki Nakagawa
Toyo Kanetsu K.K.
19-20, Higashisuna 8-Chome Koto-ku,
Tokyo, 136-8666, Japan
Shinsuke Odahara
Mitsubishi Heavy Industries, Ltd.
12, Nishiki-Cho, Naka-ku,
Yokohama, 231-8715, Japan
ABSTRACT
In October 2000, Osaka gas completed construction of a large-scale prestressed
concrete (PC) LNG storage tank at the Senboku LNG Terminal II. Given its capacity of
180,000 m3, this tank will be the world’s largest aboveground LNG storage tank, realized
by using the latest technology to increase the capacity, and reduce the cost and work
period. For the first time in the world, high-strength self-compacting concrete (SCC) has
been adopted for the entire PC wall (10,000 m3). To place as much as 1,000 m3 of
concrete at a time, the company developed manufacturing, construction and quality
control techniques in advance.
This paper presents the advanced cost-saving and work-period-reduction technologies,
with focus on the effectiveness of high-strength SCC and technologies established in
relation to it.
PS6-4.1
RESUME
OSAKA GAS est en train de construire un grand réservoir GNL en BP (béton
précontraint) dans le deuxième atelier de l’Unité de Senboku pour achever en automne 2
000. La capacité de ce réservoir étant 180 000 m3, il est le plus grand du monde en
modèle au sol. Il sera construit en utilisant la technologie de pointe de grande capacité et
des technologies de réduction de coûts et durée de la construction. Pour la paroi déversoir
en BP, 10 000 m3 de SCC (béton auto-compactage) à haute résistance sont utilisés
entièrement en mettant le compactage ultérieur inutile. Dans ce cas, des méthodes de
production, d’exécution ou de contrôle qualité ont été étudiées pour bétonner une grande
quantité de SCC à haute résistance (1 000m3/ fois).
Dans cet article, nous présenterons les dernières technologies de réduction des coûts
et de la durée de construction et principalement les techniques assurant l’effet maximum
du SCC à haute résistance.
PS6-4.2LARGEST ABOVEGROUND PC LNG STORAGE TANK IN THE
WORLD, INCORPORATING THE LATEST TECHNOLOGY—
CONSTRUCTION COST REDUCTION AND SHORTENING
OF WORK PERIOD BY EMPLOYING
NEW CONSTRUCTION METHODS
1. INTRODUCTION
Osaka Gas uses LNG as the raw material for almost all of its natural gas supplies. To
cope with seasonal fluctuations in natural gas demand and to maintain stockpiles, Osaka
Gas stores LNG in LNG tanks. Because it is necessary to store large amounts of LNG for
these purposes, expenditures for the construction of the tanks account for a major portion
of the terminal's overall construction costs. Therefore, reducing LNG tank construction
costs is one of the most important topics for lowering the costs of LNG terminal
construction. Osaka Gas has made continuous efforts to achieve this.
One way to reduce the costs of LNG tank construction is to increase the capacity of
each tank. The scale merit brought about by a larger-capacity tank reduces the overall
costs and also enables more effective use of land, which is a major management resource
in Japan. At the time Osaka Gas began using LNG, tank capacity was 40,000 m3. The
company later increased this to 80,000 m3, then to 140,000 m3. In October 2000, Osaka
Gas completed construction of a 180,000-m3-capacity LNG tank at Senboku Terminal II,
the largest above-ground LNG tank in the world.
Another approach to reduce LNG tank construction costs is to develop various
technologies that enable the efficient design and construction of tanks. Such technologies
not only reduce construction costs but also shorten the construction period.
The advanced cost-saving and work-period-reduction technologies are presented in
this paper, with focus on the effectiveness of high-strength SCC and technologies
established in relation to it.
Moreover, the construction of another 180,000-m3-capacity LNG tank is in progress
at Himeji Terminal, which commenced in March 2000. Self-elevated scaffolding and
other technologies have been developed to achieve a substantial work period reduction.
Consequently, an additional reduction is expected in construction cost per unit volume,
owing to these technologies.
2. THE DEVELOPMENT AND CONSTRUCTION OF A PC LNG STORAGE
TANK WITH INCREASED CAPACITY(180,000m3)
2.1 Abstract of the development
In developing a large-capacity tank, a high degree of reliability needs to be ensured in
every aspect, from materials and structure to construction management and quality
control. Consideration should also be given to higher safety measures for the rare event
of a leakage. Osaka Gas has undertaken the development of a new type of storage tank
with prestressed concrete (PC) outer tank which achieves increased capacity while
ensuring higher safety and reliability. After years of R&D efforts in PC tanks, and the
establishment of large capacity storage technology including the development of inner
tank material, Osaka Gas completed a 140,000-m3 PC LNG tank in 1993.
PS6-4.3Various engineering analyses have been conducted in relation to large-capacity
storage technology. Such efforts have resulted in the development of the 180,000-m3-
capacity PC LNG tank, as mentioned above, the largest above-ground LNG tank in the
world, which was completed in October 2000. (Fig. 1)
Fig.1 Overview of 180,000m3 PC LNG storage tank
2.2 The structure of the PC LNG storage tank
The structure of the 180,000-m3 PC LNG tank is shown in Fig.2. It consists of an
inner tank, an outer tank and a cold insulation material filled between the inner and outer
tanks. The inner tank that stores the LNG features a dome roof that offers excellent
resistance to earthquakes, while the outer tank roof is fixed on the upper section of the PC
liquid retaining wall. Together, they constitute a double-integrity structure. The inner tank
is made of steel with 9% Ni for high strength and toughness in low temperatures. In the
event of an LNG leak, the PC liquid retaining wall, with its low-temperature liquid-proof
performance, will contain all of the leaked LNG for safety. The inner wall and the bottom
surface of the PC liquid retaining wall are fitted with a cryogenic resistance cushioning
material that minimizes the adverse effects to the retaining wall caused by contact with
LNG, such as a sharp temperature decrease or thermal stress.
2.3 Newly-developed technologies applied to 180,000-m3-capacity PC LNG tank
Information on recent technological developments for the reduction of LNG tank
construction costs is summarized in Fig.3. The construction cost per unit volume of the
180,000-m3-capacity LNG tank built at Senboku Terminal II is 10% lower than that of
the previous 140,000-m3-capacity LNG tank. The 180,000-m3 PC LNG tank occupies a
site with an area that equals the installation site of a 75,000-m3 above-ground double-
integrity metal tank, demonstrating that the new tank utilizes land about two-and-half
times more effectively than a conventional tank.
PS6-4.4800 800
Thick50mm
Insulation
Steel liner
‚ f
‚ k
Fig. 2. Structure of 180,000m3 PC LNG storage tank
Reduction in number of shell
plate
Reduction in concrete placement and
Widened shell plate
workers
Self-compacting concrete Reduction in prestressing
no need for compaction tendons
Enlarged prestressing
tendons
Reduction in
thickness
PC LNG Tank Thick inner tank
High-strength concrete
material
Inspection technology Reduction in
for thick inner tank piles
Reduction
1353
in
1293
concrete
Technology for capacity expansion weight with high-strength
concrete
Technology for further cost reduction
Fig. 3 Performance gained by cost reduction technologies applied to
180,000-m3 –capacity PC LNG tank
PS6-4.5(1) High-strength, self-compacting concrete (Technologies for reduction in construction
cost and period)
Self-compacting concrete differs from conventionally used normal concrete in that it
requires no compaction at the time of concrete placement (Fig. 4). This results in a
reduced number of workers and a shorter work period. Moreover, further cost reductions
can be achieved by increasing the strength of the self-compacting concrete. A detailed
explanation will be given in Section 3.
Fig. 4 Property comparison between normal concrete and self-compacting concrete
(2) Enlarged PC tendons (Technologies for reduction in construction cost and period)
About 100 circumferential prestressing tendons (prestressing strands and anchorages)
are installed in the PC outer tank. By increasing the number of prestressing strands of
each tendon and thereby increasing the induced compression force of each tendon, the
number of circumferential tendons was reduced by 1/3. As a result of increased strands,
the size of anchorage blocks inevitably became larger. This would cause a decline in
toughness of the anchorage blocks in cryogenic temperatures, due to the mass effect of
the blocks during heat treatment. In order to prevent this decline, toughness tests were
carried out and Ni-Cr-Mo steel was selected as a material for the anchorage blocks.
(3) Development of inner tank material (Technology for increasing capacity)
Nine percent Ni steel is used as the inner tank material because it has superior
strength and toughness even at temperatures as low as –160°C. Since the inner tank wall
becomes thicker as the tank capacity expands, we had to produce a 9% Ni steel plate
which was thicker than anything that had been used before. 30 mm thick plates had been
used for 80,000 m3 class tanks, 40 mm thickness for the 140,000 m3 tank and, for the
180,000 m3 tank, 50 mm thick plates were used.
The strength and toughness of the thick 9% Ni steel were enhanced by introducing the
latest technologies in steel production, which helped to improve the heat treatment
process and reduce impurities. In commercializing the thick 9% Ni steel, a number of
strength and toughness tests were performed, including a low-temperature fracture test, in
order to ensure the material’s safety for use in a large-capacity tank. The development
and establishment of new technology for a 50 mm, thick 9% Ni steel has made it possible
to increase the capacity of LNG tanks.
PS6-4.6(4) Enlarged shell plates (Technologies for reduction in construction cost and period)
By expanding the width of each plate on the inner shell by 1 meter and thus reducing
the number of shell plates, the number of welding on the inner tank was reduced by 10%.
In employing large size 9% Ni steel plates, it was confirmed that uniformity is maintained
throughout the plate in terms of the material performance and dimensional accuracy.
3. USE OF HIGH-STRENGTH, SELF-COMPACTING CONCRETE (SCC)
High-strength, self-compacting concrete (SCC) was used for the 180,000-m3-capacity
LNG tank completed in October 2000 at Senboku Terminal II. The use of SCC, 60
N/mm2 in design concrete strength, for the PC liquid retaining wall was intended to
reduce wall thickness through the use of high-strength concrete, and to save labor and
shorten the work period by omitting compaction work.
3.1 Abstract of high-strength, self-compacting concrete
A comparison between the mix proportion for a prestressed concrete high dike with a
design concrete strength of 60 N/mm2, 1.5 times as large as that of the existing tank, and
the mix proportion of the self-compacting concrete used for closing the temporary
construction opening of the existing PC LNG storage tank is shown in Fig.5. Both types
of concrete contain almost the same amount of powder with a difference only in
percentages of fine and coarse aggregates by volume. A slight difference in the amount of
high-range water reducing agent results in only a small variance in the cost of concrete
material. It was then decided to construct the high dike with self-compacting concrete.
Water Powder Fine Agg. Coarse Agg. Air
Chemical admixture
Normal concrete
2
f'ck=24N/mm
Air – entraining and
Cement
22
water – reducing agents
f'ck=40N/mm
Existing PC LNG storage tank
22 Limestone powder [SPA]
f'ck=40N/mm
(Example of new - RC)
22
f'ck=60N/mm , slump 24cm
Existing PC LNG storage tank
( HPC for closing Expansive adm.
the temporary construction 2opening )
2
Limestone powder
f'ck=40N/mm
New PC LNG storage tank
(High – strength and self – compacting concrete
22
f'ck=60N/mm
Fig.5 Comparison of several mix proportions
3.2 Performance
(1) Reduction of materials
Increased concrete strength makes it possible to reduce the size of structural
components and the quantity of materials.
When the same concrete strength as that of the existing PC LNG storage tank (f’ck=40
N/mm2) is applied, and membrane stress is set at the same level, the thickness of the
PS6-4.7prestressed concrete high dike would be 110 cm for 180,000 m3, while the thickness for
140,000 m3 is 90 cm. This causes an increase in self-weight, prestressing force and
thermal stress due to low temperature. The thickness of the wall can be reduced to 80 cm
if the strength of the concrete is increased up to f’ck=60 N/mm2. As a result, concrete
volume is reduced 27%, from 13,000 m3 to 9,500 m3, and the number of foundation piles
is reduced 4.4% from 1,353 piles to 1,293 piles.
(2) Reduction in worker numbers
Labor savings are possible in concrete placement if there is no need for compaction,
that is, no need for temporary workers who are required only for concrete placement.
Labor for concrete work on the previous PC LNG storage tank, (vibrator compaction
required) entailed mobilization of temporary workers on the day of concrete placement
only.
This leads to a large percentage of the workforce compared to the normal workforce
(Fig.6). Also, the performance of compaction carried out by temporary workers is a
determining factor in the quality of the concrete high dike.
Therefore if normal concrete is used, the realization of durable and reliable concrete
structures depends on extensive site management. Concrete engineers should accompany
the whole concrete placement process to constantly provide guidance, monitor and
confirm that careful compaction has been carried out from start to finish.
On the other hand, if SCC is utilized, no temporary workers are required and
experienced workers alone can manage the concrete placement operation. Desired
concrete quality is obtained by simply inspecting at the point of receiving the ready-
mixed concrete to confirm whether the concrete is self-compacting or not. This leads to
great savings in manpower, and to a minimization of the impact of human factors on the
quality of concrete structures.
Foreman
Every day Steeple jack Smith & Constr. worker Form worker
Temporary workers
near future
The day of concrete placement Confirmation of compacting Adjustment of
form work and Pumping Plaster
(New PC LNG storage tank) operator
equipment, other
The day of concrete placement Adjustment of
Compacting and supporting form work and
(Existing PC LNG storage tank) equipment, other
0 50 100
Workers (persons)
Fig.6 Concrete placement workers
PS6-4.8(3) Reduction of work period
SCC shortens the work period through the increased placement height of each
concrete lot, which has conventionally been restricted by compaction work, and also
through the reduced number of concrete lots.
In conventional construction, the placement height of each concrete lot may not
exceed 3 m for the vibrating operation. On the other hand, with SCC, the concrete
placement height can be chosen as desired, as it is not restricted by the compaction work.
Lateral pressure along the formwork, however, may increase up to the hydrostatic
pressure of the concrete. A placement height that will minimize costs exists in practice,
with trade-offs being taken into account in relation to the structures of formwork and
shoring and the frequency of reuse. Under a construction plan based on the assumption
that the lateral pressure of concrete during placement would be identical to the
hydrostatic pressure, a placement height of 4.4 m was obtained as an optimum value. The
designed height is about 1.5 times the previous placement height. The number of lots
required for a 38.4m concrete high dike was reduced to 10 lots, 4 lots less than in
previous practice. This resulted in shorter construction period of 4 months.
4. ADVANCED TECHNOLOGIES FOR REDUCTION IN CONSTRUCTION
COST AND PERIOD
4.1 Abstract
Aiming at further reductions in cost and work period, the technologies shown in Fig.
7 have been developed for the construction of the 180,000-m3-capacity LNG tank, which
commenced in March 2000 and is in progress at Himeji Terminal. This tank is scheduled
to be completed in August 2003. The self-lifting scaffolding is explained below. In
addition, the utilization of information technology (IT) on the construction site will also
be described.
Inner tank roof plates
Reduction in thickness of reduced in thickness
outer tank liner
Use of PC for base
PC LNG tank
Self-lifting scaffolding
Use of long piles
Fig. 7 Technologies for Reduction in Construction Cost and Period Applied to
the 180,000-m3-Capacity PC LNG Tank under Construction
PS6-4.94.2 Self-lifting Scaffolding
In general, PC liquid retaining wall is built stage by stage in a vertical direction.
Scaffolding and formwork are such that their size is sufficient for the construction of each
lot. They are lifting and reused for the construction of the next lot. On the conventional
construction site of a PC liquid retaining wall, large scaffolding and formwork for the
construction of a lot are divided into 36 segments, each segment being lifted up by a large
crawler crane.
In building the PC liquid retaining wall of the tank currently under construction, the
entire scaffolding and formwork around the liquid retaining wall are lifting at once. This
is made possible by supporting the scaffolding and formwork by hydraulic jacks on rods
provided in the building frame (Fig. 8).
Owing to this contrivance, it takes only one week to complete the construction cycle
of each lot, consisting of the procedures shown in Fig. 9. The work period needed for
building a PC liquid retaining wall is reduced to half of that required by the conventional
method. Construction costs for the PC liquid retaining wall are cut approximately 10%.
These improvements are summarized in Table 1.
Concrete placement
Scaffolding and formwork Tendon sheath
lifting after removing installation
forms of last lot
1-week cycle
Placing of
reinforcement
Fig. 8 Self-lifting scaffolding Fig. 9 Lot construction procedures
Table 1 Comparison of PC liquid retaining wall construction methods
Existing PC LNG tank PC LNG tank under construction
Size of scaffolding 12m 10m
Scaffolding
Large crawler crane Jack
elevation method
Placement cycle Approx. 1 month per lot (4.3 m) Approx. 1 week per lot (1.9 m)
Period of PC liquid
retaining wall 12 months 6 months
construction
Cost reduction ∆ approx. 10% (PC liquid retaining wall construction cost)
PS6-4.104.3 Application of Information Technology (IT) on Construction
A system is built on the construction site so that the person placing the order and
contractors can share various site information in electronic form (Fig. 10). This
strengthens site management, as well as bringing benefits including a speed up or
improved efficiency in work and support to engineers at distant locations.
The Application Service Provider (ASP) for construction, which was recently
introduced into Japan as a new service in the information and communication industry, is
used as the information sharing system. As a benefit of a service offered on the Internet,
ASP enables users to share information without the need for constructing an extra
network among those placing orders and contractors.
Temperature-dependence Ready-mixed concrete
and stress-strain behaviors suppliers
PC LNG tank of PC building frame
• Material input record
• Mixer load currents
Quality management Measurement management/control
Remote-controlled camera
Work/inspection Use of ASP
manuals, inspection
records, photos, logs, (Shared information) Contractor k
and process schedules (construction site)
Contractor j Checking and
Design documents
(construction site) giving directions
Contractor k (design)
Contractor j (design)
Person placing order (site) Person placing order (headquarters)
Fig. 10 Conceptual diagram of electronic information sharing system
5. CONCLUSION
Lower costs and shorter work periods have been achieved for the 180,000-m3-
capacity LNG tank recently completed and for the one with the same capacity under
construction in comparison to the costs and time required for previous tanks, as has been
shown above. A summary of the reductions in costs and work periods is shown in
following.
• Technology for increasing capacity:
Ø Development of inner tank material
• Technologies for reduction in construction cost and period:
Ø High-strength, self-compacting concrete
Ø Enlarged PC tendons
Ø Enlarged shell plates
Ø Self-lifting scaffolding
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