Conference on High Strength Steels for Hydropower Plants - Takasaki
Construction of Steel Penstocks using HT100
at Kannagawa Hydropower Plant
Ken-ichiro AOKI1 and Masayuki MINAMI1
1
Tokyo Electric Power Company, Japan
Introduction
Tokyo Electric Power Company’s Kannagawa Hydropower
Plant is located in Gunma prefecture, Japan.
For the first challenge in Japan, high tensile strength steel
(HT100) with a tensile strength of 950 N/mm2 was adopted
for use in the penstocks of Kannagawa Hydropower Plant to
reduce the construction cost. To apply HT100 steel for the
penstocks, a performance verification test was conducted in
advance to make sure that HT100 steel plates and welded
joints have required performance, while the requirements for
welding procedures were determined. In the actual
construction, quality control was carried out adequately on
the basis of the determined requirements for welding
procedures and other requirements.
This paper presents the design and construction of the
penstocks of the Kannagawa Hydropower Plant. In the paper,
we primarily focus on quality control items specified in
consideration of the characteristics of high tensile strength
steel and their results.
surge tank, into the penstock for units 1 & 2 with a total
length of 1,397 m and the penstock for units 3 & 4 with a
total length of 1,365 m.
Tokyo Electric Power Company decided to introduce high
tensile strength steel (HT100) with a tensile strength of 950
N/mm2 for the penstocks of its Kannagawa Hydropower
Plant to reduce the construction cost. Table 1 shows the
materials used and their weight. The total weight for units 1
& 2 penstock was about 5,154 t, of which the quantity of the
HT100 steel was about 2,331 t. The total weight for units 3 &
4 penstock will be about 5,150 t, of which the quantity of the
HT100 steel will be about 1,420 t.
The construction of the penstock for units 1 & 2 was started
in April 2001, with the installation on the site completed in
July 2004. Currently, the inclined shaft and part of upper and
lower horizontal sections of the penstock for units 3 & 4 are
under construction with the progress rate being about 40% as
of May 2009; the installation of the penstock is planned to be
completed by April 2010.
1. Overview of Facilities
Tokyo Electric Power Company’s Kannagawa Hydropower
Plant is a pure pumped-storage power plant with an effective
head of 653 m generating a maximum output of 2,820 MW
with six motor-generators. Its unit 1, with a maximum output
of 470 MW, was put into commercial operation in December
2005.
The steel penstocks of the Kannagawa Hydropower Plant are
embedded in rock mass, extending over a length of about
1,400 m with a difference in elevation of 745 m and having a
maximum design head of 1,076 m, of which the static head is
817 m, and inside diameters ranging from 2.3 m to 8.2 m.
The steel penstocks consist of upper horizontal section,
inclined shaft section, and lower horizontal section.
The inclined shaft section of the entire penstock structure is
an about 960m long steep gradient pressure conduit, with an
inclination of 48 degrees and an inside diameter of 4.6 m.
Figure 1 shows a schematic diagram of the steel penstocks of
the Kannagawa Hydropower Plant. The steel penstock is
bifurcated, at the Branch I located at the base of the headrace
1-1
Figure 1: Schematic diagram of the steel penstocks of
the Kannagawa Hydropower Plant
Conference on High Strength Steels for Hydropower Plants - Takasaki
TABLE 1: Materials and weights of steel
Steel
HT100
SHY685
NS-F
SM570
SM490B
TABLE 2: Allowable stress and yield point of steels
4)
Penstock for units 1 & 2
Penstock for units 3 & 4
Thick
ness
(mm)
29-72
28-38,
621)
2002)
Thick
ness
(mm)
27-72
28-42,
621)
2002)
22-45
20-52,
703)
-------
Weight
(t)
2331
Ratio
of
weight
45%
312
8
6%
1335
26%
1168
23%
22-44
22-52,
703)
22-26
Weight
(t)
1420
Ratio
of
weight
28%
<75
Allowabl
e stress
(N/mm2)
400
Yield
point
(N/mm2)
885
<50
50-100
200
16-40
40-75
16-40
40-100
16-40
40-100
330
320
315
240
235
175
160
130
115
685
665
650
450
430
315
295
235
215
Steel
Thickness
(mm)
HT100
SHY685NSF
907
8
18%
1541
30%
1148
22%
SM570
SM400B
---0%
126
2%
Total
5154
100%
5150
100%
weight
1) 62-mm thick steel is for joining inlet valves.
2) 200-mm thick steel is for stiffening the branch II.
3) 70-mm thick steel is for reinforcing the branch I.
4) The penstock for units 3 & 4 is now under construction, so the values are
estimated.
SM490B
SM400B
Standard
Technical
Guidline
for
HT100
JIS G
3128
JIS G
3106
JIS G
3106
JIS G
3106
2. Design of the Penstocks
2.1 Design for Internal hydraulic pressure
In the design of penstocks embedded in rock mass, internal
hydraulic pressure is partially borne by rock mass
surrounding penstocks with the aim of reducing costs
through a reduction in the thickness of steel pipes.
In this design, the ratio of internal pressure borne by rock
mass is designed according to rock mass properties, such as
the elastic modulus and plastic deformation coefficient. The
plate thickness of the penstock is determined so that the
stress acting on the penstock as a result of the consideration
of the internal pressure borne by rock mass may not exceed
the allowable stress of the penstock. In addition, the design is
established on the safe side so that the stress acting on the
penstock may not exceed the yield point of the steel material
even if rock mass is assumed to bear no internal hydraulic
pressure.
Table 2 shows the allowable stress and yield point for the
steel material used.
Joint efficiency is determined for the places of welding and
the sampling ratio in the nondestructive inspection, and can
be made 100% by welding in a workshop and inspection over
the entire welded length.
Tokyo Electric Power Company compared costs of
nondestructive inspection over the entire welded length with
reducing costs through a reduction in the thickness of steel
pipes assuming a 100% joint efficiency. For the penstocks
used in the Kannagawa Hydropower Plant, a reduction in the
plate thickness was adopted by assuming a 100% joint
efficiency after the inspection of entire longitudinal joint
lines.
2.2 Design for External hydraulic pressure
To ensure safety for external hydraulic pressure, penstocks
embedded in rock mass are designed to have a safety factor
of 1.5 or more against the critical buckling pressure
calculated using the theoretical formula.
For inclined shafts of which an adequate drain slope can be
expected, Tokyo Electric Power Company adopts a design in
which drain facilities are installed to reduce external
hydraulic pressure.
Figure 2 shows the design of the drain facilities of the
Kannagawa Hydropower Plant. The drains consist of both a
direct drain for draining water from the void between the
penstock and the infilling concrete and an indirect drain for
draining seepage water, which comes from the rocks, from
the void between the concrete and the rocks. Even when one
of the drains becomes ineffective, the other reduces the
external hydraulic pressure to prescribed level.
The groundwater level in the natural ground surrounding the
penstocks is assumed to be on the grand level according to
investigation. The drain facilities are designed to reduce the
groundwater potential near the penstock in the inclined shaft
section. For the penstock for units 1 & 2, the design external
hydraulic pressure was set at 40% of the hydraulic pressure
corresponding to the natural ground cover on the basis of the
two-dimensional seepage flow analysis. For the penstock for
units 3 & 4, on the other hand, with the aim of reducing plate
thickness, the design external hydraulic pressure was set at
30% of the hydraulic pressure corresponding to the natural
ground cover because a ratio of the measurement value for
the design external hydraulic pressure of the penstock for
units 1 & 2 was very small.
1-2
Conference on High Strength Steels for Hydropower Plants - Takasaki
2.3 Results of the Design
In designing the material and plate thickness of penstocks,
the plate thickness was decided as follows;
First, the largest plate thickness, for each unit section (with a
length of 3 m), was calculated by each candidate material
among ;
(1) plate thickness dictated by the internal hydraulic pressure,
(2) plate thickness dictated by the external hydraulic
pressure, and (3) the smallest plate thickness dictated by the
restrictions in construction.
Then, the most cost-effective material was decided with the
costs for materials, manufacturing and installation taken into
account. In addition, while welding workability was being
given consideration to avoid an abrupt change in plate
thickness and an extreme change in the material between
adjoining unit sections, materials and design plate thickness
were adjusted adequately before determining the final design.
Figure 3 shows the results of the design of the penstock (for
the inclined shaft) of the Kannagawa Hydropower Plant. For
the penstock for units 3 & 4, the plate thickness of HT100
steel is smaller than that of the penstock for units 1 & 2 as a
result of a review of design conditions such as a change in
the design external hydraulic pressure.
Figure 2: Design of the drain facilities
Penstock for units 3&4
Penstock for units1&2
①SM400
②SM490
③SM570
④SHY685
⑤HT100
Figure 3: The design of the penstock (for the inclined shaft)
1-3
Conference on High Strength Steels for Hydropower Plants - Takasaki
3. Procedure of the penstock installation
Figure 4 shows an overview of the penstock installation of
the Kannagawa Hydropower Plant.
The penstocks were constructed by cutting steel plates,
preparing edges and bending the plates in manufacturer’s
plant. And then, due to transportation limits, these were
constructed by transporting the half-pipe parts to the site,
welding the parts into 3 m-long unit pipes and then into 15
m-long unit pipes in the temporary workshop at the site, and
installing in the inclined shaft and welding the unit pipes.
The installation of steel penstock in the inclined shaft was a
critical path of the construction schedule. Since the adoption
of HT100 steel allowed one to reduce the penstock weight in
the inclined shaft section, the length of an installation unit
pipe was increased from 12 m (four 3-m long unit sections),
the longest in the past, to 15 m (five 3-m long unit sections),
thereby reducing the number of times of installation in the
inclined shaft and hence reducing the time necessary for
installation by 20%.
In the inclined shaft, a construction method that was based on
the installation of two unit pipes taken as one work cycle was
adopted. Consequently installing steel a unit pipe and filling
concrete helped shorten the construction period. The
installation speed of HT100 steel sections including concrete
filling was 11 days/30 m. The mean installation speed of the
entire inclined shaft was 10 days/30 m.
Regarding the weld processes adopted for the penstocks at
the site, the SAW(submerged arc welding) method was
adopted for straight pipes and the SMAW(shielded metal arc
welding) method for bend pipes at the temporary workshop,
while the method of automatic MAG(metal active gas)
welding from one side of the inner surface was adopted for
the inclined shaft, with the SMAW method adopted for other
on-site welding operations.
obtained during the construction on the penstock for units 1
& 2 for examples.
Figure 4: Overview of the penstock installation
Place
Steel penstock installation procedure
Inspection
Material making
Steel mill
Material Inspection
Workshop of
fabricator
Half pipe manufacturing
Half pipe Inspection
（
transportation
）
Receiving&Inspection
Unit pipe of 3m fabricating
Assembly
Groove Inspection
Longitudinal welding
Visual Inspection
4. Quality Control for the Penstocks
Nondestructive Inspection
Temporary
workshop
4.1. Overview of Quality Control for the Penstocks
To apply HT100 steel for the penstocks, Tokyo Electric
Power Company primarily focused on the prevention of
brittle fracture, while quality control items and criteria for
steel plates and welded joints were determined, especially in
consideration of toughness and weldability.
Figure 5 shows the penstocks installation procedure and
important inspection items of quality control for the
penstocks of the Kannagawa Hydropower Plant. Tokyo
Electric Power Company’s approach to quality control is
fundamentally based on both the checking of all records of
inspection by the fabricator and witness sampling inspection.
In addition to this, specifically for important inspection
items, the witness inspection of all articles is predominantly
used. In the following, the important items and results of
quality control are described using the pieces of data
Unit pipe of 15m fabricating
Asssembly
Groove Inspection
Circumferential welding
Visual Inspection
Dimension Inspection
Nondestructive Inspection
Painting
Before painting Inspection
After painting Inspection
Installation
Assembly
Groove Inspection
Inclined
shaft
Circumferential welding
Visual Inspection
Nondestructive Inspection
Completion
Figure 5: Important inspection items of quality control
for each procedure
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Conference on High Strength Steels for Hydropower Plants - Takasaki
4.2 HT100 Steel Plates and Welding Materials
Table 3 and Figure 6 show the quality control criteria and test
results for HT100 steel plates. Generally tensile strength tests
are conducted using C-direction of the steel plate. However,
the preliminary performance verification test revealed that
the L-direction strength bearing hydraulic pressure tended to
be smaller than the strength in the C-direction in HT100
steel. In the actually executed work, for this reason, the
tensile strength test was conducted both in the L- and Cdirections. Since the impact test also showed that the
toughness near the middle of the plate thickness tended to
be inferior to that at the 1/4-thickness position, the toughness
was checked at positions of 1/4-thickness and 1/2-thickness
in the actual construction.
Table 4 shows the mechanical properties of HT100 deposited
metal and the control standard for the quantity of hydrogen.
The specifications of the deposited metal were characterized
by tensile strength for which slightly softer nature than the
base metal was required in consideration of the balance with
the toughness and weldability and by the requirement for the
quantity of hydrogen.
TABLE 3: The quality control criteria and test results for HT100 steel plates
Element
Plate thickness <= 50mm
n=41
C
P
S
PCM
Plate thickness > 50mm
n=12
C
P
S
Ceq
Ceq
PCM
Maximum
0.11
0.008
0.001
Minimum
0.09
0.001
0.001
0.572
0.273
0.12
0.006
0.001
0.603
0.311
0.533
0.254
0.11
0.002
0.000
0.592
0.288
Maximum
content
0.14
0.01
0.005
0.59
0.29
0.14
0.01
0.005
0.62
0.33
Ceq=C+Mn/6+Si/24+Ni/40+Cr/5+Mo/4+V/14
PCM=C+Si/30+Mn/20+Cu/20+Ni/60+Cr/20+Mo/15+V/10+5B
Figure 6: The quality control criteria and test results for HT100 steel plates
1-5
Conference on High Strength Steels for Hydropower Plants - Takasaki
TABLE 4: Mechanical properties of HT100 deposited metal
and the control standard for the quantity of hydrogen.
Welding method
SMAW
SAW
MAG
Yield strength
(N/mm2)
Tensile strength
(N/mm2)
Elongation (%)
Charpy impact
absorption energy
(J)
≧ 785
≧ 785
≧ 785
(Reference)
HT100
steel plate
≧ 885
930-1000
930-1000
930-1050
950-1130
≧ 12
≧ 47
(at –10℃)
≧ 12
≧ 47
(at -10℃)
≧ 12
≧ 47
(at -10℃)
≧ 12
≧ 47
(at -55℃)
≧ 50
≧ 50
≧ 50
≧ 50
≦6
≦3
≦2
----
Ductile fracture
percentage (%)
Hydrogen content
(mL/100g)
completion of welding operation. However, postheating was
indispensable for preventing cracks for HT100 when preheat
temperature was similar to that for SHY685NS-F.; and
c. Use of welding materials for SHY685NS-F in single pass
welding by SMAW and MAG enabled preheat temperature
for preventing cracks to be lowered. Thus, use of welding
materials for SHY685NS-F in SMAW and MAG for root
pass welding and tack welding was effective for preventing
cracks.
For SM570 and SM490B, a special specification of weld
crack sensitivity PCM against weld cracking of not exceeding
0.2% was also applied, and preheating was omitted except on
cold days.
Table 6 shows the track records of heat input control for
HT100 welded joints. Compared with the control standard of
45 kJ/cm, the average heat input in the actual construction is
about 34 kJ/cm in the SAW and SMAW methods and about
16 kJ/cm in the automatic MAG method applied in the
inclined shaft.
In controlling the welding atmosphere, the water vapor
pressure was calculated from the results of measurements of
the ambient temperature and humidity, and the relationship
between the values obtained and the control standard was
used in order to limit the time for which the welding
materials were left alone. Figure 7 shows the track records of
the control of water vapor pressure at the temporary
workshop.
4.3 Welding Procedure Control
Table 5 shows the requirements for welding procedures. The
requirements for welding procedures for HT100 steel were
specified on the basis of the results of the preliminary weld
cracking test. The results of the weld cracking test showed
the following findings:
a. In single pass welding, the preheat temperature for
preventing weld cracking was similar or higher in a U-groove
weld cracking test than in a y-groove weld cracking test.
Thus both tests should be conducted to determine preheat
temperature for HT100.
b. A multi-layer weld cracking test showed that postheating
(150°C for 2 hours) was highly effective for preventing
cracks. In SHY685NS-F, postheating could be omitted when
a nondestructive test was conducted at over 48 hours after the
TABLE 5: The requirements for welding procedures
Steel
Thickness
(mm)
HT100 and
SHY685NS-F
Not
exceeding
50
Over 50
Minimum preheating
temperature (°C)
SMAW
MAG
SAW
100
80
125
100
Interpass
temperature
Limit heat input
(kJ/cm)
Postheating
conditions
At least the
preheating
temperature
and not
exceeding
230°C
----
The mean not
exceeding 45, and
the maximum not
exceeding 50
At least 2
hours at over
150°C
No preheating
Not
Not exceeding 60
---exceeding
25
Over 25
---Not exceeding 80
---SM490B
------------SM400B
------------a. For SMAW and MAG for HT100, welding material for SHY685NS-F was used for root pass and tack welding.
b. For tack welding of HT100 and SHY685NS-F, welding materials of a strength level that was one rank lower than that for the
actual welding.
c. Postheating was omitted for SHY685NS-F if nondestructive test was conducted 48 hours after welding or later.
d. The preheating temperature for tack welding was at least 25°C higher than the minimum preheating temperature stated above.
e. In SMAW and SAW, the preheating temperature was at least 25°C higher than the minimum preheating temperature stated above
when the partial hydraulic vapor pressure was over 25.5 mmHg.
f. For SM570 and SM490B, steels with PCM of not exceeding 0.2% was used and no preheating was conducted provided that the
temperature was preheated to 40°C when the air temperature was 5°C or below.
g. When welding was suspended, postheating was preformed using the conditions stated above or the temperature was retained until
welding was restarted.
SM570
1-6
Conference on High Strength Steels for Hydropower Plants - Takasaki
TABLE 6: The track records of heat input control for HT100 welded joints
Place of welding
Welding
method
Number
of joints
Average heat input (kJ/cm)
365
Pass maximum heat input
(kJ/cm)
Max.
Min.
Average
48.4
30.9
39.1
Temporary
workshop
Temporary
workshop
Field
Inclined shaft
Control standard
SAW
Max.
39.8
Min.
27.7
Average
32.8
SMAW
20
48.4
41.1
27.2
36.3
SMAW
MAG
87
25
49.1
26.6
39.9
37.6
24.6
30.1
Not exceeding 50
37.9
45.0
38.9
19.9
32.0
18.5
13.1
16.4
Not exceeding 45
Water vapor
pressure(mmHg)
40
Contorol Standard：25.5mmHg
30
20
10
0
2001/11/1 2002/1/31 2002/5/2
2002/8/2 2002/11/1 2003/1/31 2003/5/3
2003/8/2 2003/11/1 2004/2/1
2004/5/2
2004/8/1
Date
Figure 7: The track records of the control of water vapor pressure at the temporary workshop
Offset ratio for thickness(%)
4.4 Offset and Angular Distortion of Welded zones
From the viewpoint of preventing brittle fracture, checking
the shape of welded zones inducing the stress concentration
is one of the most important control items. In the actual
construction, quality control was conducted on undercuts,
overlaps, reinforcement weld heights, offsets, angular
distortions and so forth. Among these, the offset and the
angular distortion of a longitudinal joint were put to
quantitative control. Figure 8 shows the track records of
control of offsets and angular distortions of welded zones of
HT100.
6.0
Control Standard ≦5%
5.0
≦3mm
4.5 Nondestructive Inspection
The Japanese standards require that welded zones in the main
pressure bearing parts of a penstock be put to nondestructive
inspection after welding operation as needs arise, and that the
methods of nondestructive inspection be based on the
radiographic test or ultrasonic test as a rule. Table 7 shows
examples of the criteria (for lineal flaws) for the radiographic
test and ultrasonic test.
(1) Nondestructive test on the penstock for units 1 & 2
The nondestructive inspection on welded zones of the
penstock for units 1 & 2 of the Kannagawa Hydropower
Plant was conducted according to the following policies in
consideration of the track records of inspection on penstocks:
4.0
a. The main pressure bearing parts should be put to the
radiographic inspection as a rule; and
3.0
2.0
b. Branch pipe shells and reinforcement beam connections to
which the application of the radiographic inspection was
difficult due to structural problems should be put to the
ultrasonic test.
1.0
0.0
20
30
40
50
60
Plate thickness(mm)
70
80
3.0
Angular distortion(°)
Control Standard ≦2.5°
2.5
TABLE 7: Examples of the criteria (for lineal flaws) for
the radiographic test and ultrasonic test
2.0
1.5
Thickness
t (mm)
Not exceeding 50
1.0
0.5
Over 50
0.0
20
30
40
50
60
Plate thickness(mm)
70
80
Figure 8: The track records of control of offsets and
angular distortions of welded zones of HT100
1-7
RT (for linear flaws)
UT
Not exceeding t/3 and
16 mm
Not exceeding t/4 and
12 mm
Not exceeding
t/2 and 30 mm
Conference on High Strength Steels for Hydropower Plants - Takasaki
Table 8 shows the rules for the time to conduct
nondestructive tests on the penstock for units 1 & 2. In
consideration of the occurrence of delayed cracking in high
tensile strength steels having performance equal or superior
to that of SHY685NS-F, the time to conduct nondestructive
test was specified.
Table 9 shows the track records of nondestructive tests on the
penstock for units 1 & 2. Nondestructive tests over entire
lines were conducted on longitudinal joints bearing hydraulic
pressure with the aim of rationalizing the design by means of
setting the joint efficiency at 100%. For branch pipes with
complicated structures that require a high welding skill,
nondestructive tests were conducted on entire weld lines. For
HT100 steel circumferential joints, entire line inspection was
conducted at the beginning of welding operations, and the
rate of inspection was reduced to about 10% after the quality
of welding had been verified. These inspections allowed one
to make sure that all welded joints satisfied the criteria.
tester.
Figure 9 shows how the ultrasonic test is carried out. With
the tester introduced this time, flaws detecting operation is
carried out from both sides on one face of a welded zone
simultaneously. First, flaws are searched for coarsely, square
by square, at intervals of 5 mm, and if reflected echoes are
detected, flaw detection is carried out finely at intervals of 1
mm again. All items of obtained data are recorded in the
form of electronic data, and the judgment of data on flaws is
carried out automatically.
Rules for the time to conduct nondestructive inspection for
the penstock for units 3 & 4 (Table 8) and the rate of
execution of nondestructive inspection on longitudinal joints
(conducted over entire lines) are the same as those for the
penstock for units 1 & 2.
TABLE 8: Rules for the time to conduct nondestructive tests
Steel
HT100
SHY685
NS-F
Place of
welding
All places
Inclined shaft
Temporary
workshop
SM570,
SM490B
SM400B
All place
Time of testing
At least 24 hours
after the completion
of welding
At least 24 hours
after the completion
of welding
At least 48 hours
after the completion
of welding
No rules
Postheating
conditions
150°C for at least
2 hours
None
None
HT100
Branch II
Entire length
129.906(m)
JIS standard materials
General penstock body
Longitudinal joint Circumferential joint
Entire length
12% of the welded length
2090.011(m)
670.173(m)
Conclusion
150°C for at least
2 hours
TABLE 9: The track records of nondestructive tests
General penstock body
Longitudinal joint Circumferential joint
Entire length
57% of the welded length
1034.737(m)
1560.779(m)
Figure 9: Automatic ultrasonic test equipment
Branch I
Entire length
281.031(m)
(2) Nondestructive test on the penstock for units 3 & 4
With the aim of increasing the work efficiency and
decreasing construction costs, the ultrasonic test based on an
automatic ultrasonic tester was adopted for the
nondestructive inspection on welded zones in the
construction of the penstock for units 3 & 4 of the
Kannagawa Hydropower Plant. Before introducing an
automatic ultrasonic tester, tests were conducted on
artificially flawed test pieces to verify the performance of the
First challenge of introducing HT100 steel with tensile
strength of 950 N/mm2 to penstocks of a hydropower plant in
Japan was started at Kannagawa Hydropower Plant.
Especially in case of utilizing new materials, quality
management is the key issue to complete the project without
fatal defects since many unexpected phenomena might
happen and counter measures should be taken immediately
for completion of the project.
In Kannagawa, therefore, quality management system was
established by close cooperation between Tokyo Electric
Power Company as the owner, engineer and fabricator with
support of steel mill. At the any stage of the construction,
quality control was been made jointly.
Tokyo Electric Power Company’s approach to quality control
is based on deciding control items and criteria, carrying out
the witness inspections, and analyzing their results. The
quality control was conducted from the viewpoint of not only
judging the results for control criteria but also improving
control criteria and our design.
As the result of these efforts, the construction of the penstock
for units 1 & 2 completed successfully and no irregular stress
and strain has been observed by measuring system since
starting operation of unit 1 in December 2005.
The construction of the penstock for units 3 & 4 is now on
going, and the effort for quality management will be also
continuing until completing the construction with achieving
targeted quality successfully.
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