Features of full-welded steel water tank and its earthquake resistanceYoshihide YAMADA*, Susumu HASHIMOTO*** General Manager, Design and Development Department, NYK Co., Ltd., 1689-1, Negane,Hasuda City, Saitama, 349-0131** General Manager, Quality Assurance Department, NYK Co., Ltd., 1689-1, Negane, Hasuda
City, Saitama, 349-0131
Keywords：full-welded steel water tank, water reservoir, non-solvent epoxy lining, earthquake
resistance

1. Introduction
Steel water tanks have a long history withchanging structures, construction methods
and corrosion prevention measures dependingonthe
historicalbackgroundandtechnological innovations.
For example, painting with red lead paintand zinc hot-dip galvanizings had been used
to prevent corrosion originally, and wasreplaced with metallic spraying in the late
1920s. Then, epoxy coating began to be usedaround 1959 and continued to be used alongwith improvement of coating materials. With
regard to structures and construction methods,
riveting and gas welding was used at first andthen replaced with covered arc welding sincearound 1946. From around 1965, welding or
bolting of mold panels became common
construction methods 1). Then, full-weldedsteel water tanks were launched on themarket around 1977 and became themainstream in the current market of steel
water tanks.
Table 1 shows a brief history of steel watertanks. In the following sections of this paper,the outline and general features of NYK
full-welded steel water tanks are described,
focusing on their earthquake resistance.

2. Structure of full-welded steel watertanks
A full-welded steel water tank consists of asteel can body, and an epoxy lining film
covering it. The outline and general features
are as follows (see Figure 1, 2):
2.1 High-strength can body・ A can body consists of a corrugated top
panel, corrugated sidewalls and an arc
bottom panel each of which is attached bybutt welding and fillet welding on bothsides. Welding from a can body to a pipe
connecting port forms an integrated
structure.
・・Not internally-reinforced in generalsizes.
No platform at the bottom which isprovided for water tanks made of othermaterials. A skirt under a bottom panel
is regarded as a platform. An integratedstructure up to the base which is fixedwith the foundation with anchors
increases the reliability of earthquake
resistance.

Table 1
Year Historical background and brief historyof steel water tanks
1940 Arc welding was introduced as aconstruction method (1946).
1950 The Water Supply Act was issued (1957).
□ Epoxy coating was introduced as acorrosion prevention method (1959).
1960 □ Panel water tanks constructed bybolting and on-site welding werelaunched on the market (1965).
1970 The Building Standards Act was revised(1975).
The Public Notice of the Ministry ofConstruction No.1957 came into force(1976).
■ Full-welded steel water tanks werelaunched on the market (1977).
1980 The Enforcement Order of the BuildingStandards Act was revised (1980).
The New Anti-Seismic Design Act cameinto force (1981).
■ Custom-designed water tanks werelaunched on the market (1989).
1990 Large steel water tanks were launched on
the market (1993).
Great
Hanshin-Awaji
Earthquake
occurred (1995).
■Water tanks with emergency shutoff
valves were launched on the market(1997).
Water tanks accommodating watersupply trucks were launched on themarket(1998).
2000 The Mid Niigata Prefecture Earthquake
occurred (2004).
■ Full-welded steel unit water tanks
were launched on the market (2006).
The Noto Hanto Earthquake occurred(2007).
The Niigataken Chuetsu-Oki Earthquake
occurred (2007).
□Steel water tanks■Full-welded steel water tanks

2.2 Long-life lining film
・ Grit blasting for surface preparation
enhances the adhesion between thelining film and steel panels.
・ An epoxy lining film is applied on theouter and inner surface of tanks with anon-solvent hot airless spray. Afterapplication, it is heated at 120℃ for 4hours, and hardens to form a solid lining
film with a smooth surface.
Epoxy can be hardened at ordinary
temperature or by baking. In general,hardening by baking superior properties
and water resistance.
・ The standard film thickness inside oftanks is set to 0.4 mm or more.

Figure 1 Outline view

Steel plate(blasting on inner and outersurfaces)
Water storage

Epoxy lining (inner surface)
Epoxy coating (outer surface)

Figure2 Schematic cross-sectional view
Figure 1 Outline view

3. Custom-designed water tanks
As a main feature, full-welded steel watertanks can be designed freely, and it ispossible to produce water tanks likemonuments (custom-designed water tanks).
The function and performance ofcustom-designed water tanks is the same asthat of rectangular tanks. In such tanks, pipes
are contained inside and cannot be seenoutside. This construction method aims toprevent compromising the design of the tankwhile serving as a tamper-resistant function.
Moreover, it does not need concrete walls
and fences which are normally requiredaround tanks, thus providing an advantage interms of cost.
Furthermore, it is also possible to produce
free-formed water tanks depending on theshape of the site, and water tanks with wall
paintings on the outer surfaces.
The following pictures are examples ofcustom-designed water tanks and free-formed
water tanks (see Picture 1-5):

Picture 3 Water tank decorated with acorporate logo (Awarded the 2nd
Environmental and Equipment DesignAward)

Picture 4 Shinkansen-shaped water tankPicture 1 KKR Hotel Biwako
Picture 5 Free-formed water tank(with wall paintings)

Picture 2 Rocket-shaped water tank

4. Disaster control
The purpose of a water supply tank is to“provide drinking water” to buildings. It is
critical to maintain this function even when
essential utilities are damaged in the event ofearthquakes or other disasters.

4.1 Water tanks with excellent earthquake
resistance
As mentioned above, the robust structureof full-welded steel water tanks provides
excellent earthquake resistance. If water does
not leak from a water reservoir at anevacuation site, holding 10 tons of water,
about 1,000 people are provided withdrinking water for 3 days 2). In fact, NYK
full-welded steel water tanks had noproblems such as damage and water leakage
during Great Hanshin-Awaji Earthquake, TheMid Niigata Prefecture Earthquake, the Noto
Hanto Earthquake and the Niigata ken
Chuetsu-oki Earthquake, and fulfilled thepurpose of water tanks in an emergency. The
detailed situation in an actual earthquake is
described in the next chapter.
4.2 Emergency shutoff valves
The system of emergency shutoff valves is
to close valves when a preset acceleration isdetected to keep water inside a tank. Water
runoff caused by piping damage can beprevented by installing this system on watertanks.
4.3 “Water reservoir accommodatingwater trucks” enhance water supply
efficiency
Water tanks are provided with water fromwater trucks (mainly with a capacity of 2 to 4tons) for an emergency water supply (seePicture 6). However, it is difficult to takewater to large capacity water tanks because
the water level hardly rises.
To address this problem, “water reservoirs
accommodating water trucks” are available inwhich walls (water level adjustment walls)
are installed inside so that the water level canrise even with the water volume from watertrucks (see Figure 3).
They are normally used as water reservoirs,
thus offering advantages in terms of storage
space and maintenance cost compared withsimple water tanks for emergency watersupply. In addition, water hose connecting
ports and emergency water intake openings
can be provided at any locations on thereservoir. This enables reservoirs to takewater from water trucks and utilize it more
effectively.
Recently,such“waterreservoirs
accommodatingwatertrucks”
areincreasingly being introduced together withthe emergency shutoff valves mentioned
above.

Picture 6 Emergency water supply at healthcare facility for the elderly during The Niigata
ken Chuetsu-oki Earthquake (Kashiwazaki
City, intensity 6, upper division)

Water level adjustment wall

Figure 3

5. In the event of an earthquake
This chapter describes an example of theresult of post-earthquake investigations
which NYK conducted. No problems due todamage or water leakage were found in any
NYK units.
Figures 4 through 7 are based on the“Distribution of seismic intensity 7 from fieldinvestigation” and the “Estimated seismic
intensity map” by the Japan MeteorologicalAgency.
Types of buildings and names of places in
the captions of pictures are those at the timeof the earthquakes.

5.1 Great Hanshin-Awaji Earthquake (TheSouth Hyogo Prefecture Earthquake)
Picture 8 Municipal elementary school(Nishinomiya City) Point B in the figure:
Intensity 7Figure 4

Picture 9 Municipal junior high school(Higashi-Nada Ward, Kobe City) Point C in
the figure: Intensity 7

5.2TheMid
Niigata
Earthquake in 2004

Picture 7 Municipal junior high school(Takarazuka City) Point A in the figure:
Intensity 7

Figure 5PrefecturePicture 10 Municipal junior high school(Kawaguchi City) Point D in the figure:
Intensity 7

Picture 13 Care facility for the elderly (OjiyaCity) Point G in the figure: Intensity 6, upperdivision

5.3 The Noto Hanto Earthquake in 2007

Picture 11 General government office(Tokamachi City) Point E in the figure:
Intensity 6, upper division
Figure 6

Picture 12 Prefectural hospital (NagaokaCity) Point F in the figure: Intensity 6, lower
division
Picture 14 Municipal hospital (Wajima City)
Point H in the figure: Intensity 6, upperdivision

5.4
TheNiigatakenEarthquake in 2007

Chuetsu-oki

Figure 7

Picture 15 Municipal elementary school(Kashiwazaki City) Point I in the figure:
Intensity 6, upper division

Picture 16 Welfare facility for the elderly(Kashiwazaki City) Point J in the figure:
Intensity 6, upper division

6. Environmental protection
Environmental protection efforts arepromoted in full-welded steel water tanks inthe following ways:
6.1 Long-life
The combination of a robust can body witha full-welded steel structure and non-solvent
lining material permits the construction oflong-life water tanks. Moreover, thenon-solvent material provides an excellent
working environment without affecting
workers and dispersing odor to thesurroundings.
A water reservoir which was delivered at
the beginning of the launch of the sale has
still been used for over 30 years (see Picture
17 and 18). An over 60 years product life
cycle is expected for film in the accelerating
test, which is the same lifetime as that ofbuildings.
The prolonged product life cycle means
reduction of industrial waste and saving ofresources and energy.
6.2 Re-use
Full-welded steel water tanks have astructure (steel panels) covered by a lining
material, so that fatal damage to water tanks
hardly occurs. Therefore, they can be re-usedby retrieving and re-applying the lining
material.
The general procedure for re-use is asfollows:(1) Recovering and taking back the watertank to the NYK plant.
(2) Conducting
avisualinspection.
Remodeling a tank by adding orremoving nozzles and other components,
as necessary.
(3) Performing blasting to remove theexisting lining film.
(4) Applying the lining.
(5) Painting the outer surface depending on
the installation environment.
(6) Delivering and installing the tank.

In this way, as the same epoxy lining
material can be applied by the same process
as that used in the production of a new tank,the same quality is achieved for the lining ofa re-applied tank which can be re-used for along time.
The re-use of water tanks eliminates theneed to produce a new can body, thus saving
resources and energy.

6.3 Recycling
It is easy to recycle NYK full-welded steel
water tanks because SS400 steel, a common
material for structures, is used. No special
facilities are needed for recycling. Tanks arerecycled in a general method bydisassembling, melting in a furnace andre-forming as steel products.

Picture 17 Full view

Picture 18 Picture of inside of water tanktaken from a manhole

7. Conclusion
Despite of their excellent earthquake

resistance and durability, the market share offull-welded steel water tanks is still small inthe building equipment industry. NYK willcontinue to make efforts for further
enhancement of functions and improvementof technologies. Our mission is to produce
and sell more excellent full-welded steel
water tanks, and we believe that this willcontribute to the well-being of the society
and the global environment.

1)2)

References“Technical History of Air-Conditioningand Sanitary Equipment”, the Society ofHeating, Air-Conditioning and SanitaryEngineers of Japan“Tokyo Local Disaster Prevention Plan
(Earthquake Version), Section 3”, theTokyo
Metropolitan
DisasterManagement Council