SECTION 13205 - WELDED STEEL WATER STORAGE TANK
PART 1
1.01
GENERAL
SCOPE
A. This section covers the construction of steel water storage ground tank in conformance
with AWWA D-100 “Welded Steel Tanks for Water Storage”, latest edition, including
Section 13 for seismic design. All components shall comply with NSF/NSF61, Drinking
Water System Components – Health Effects in addition to Safe Drinking Water Act.
B. The tank site is not accessible by rail. The access to the site is provided by a private
road owned by the City. The construction of the tank will require re-alignment of an
existing road as shown in the drawings. The Contractor shall complete the construction
of the road re-alignment work before start of construction of the tank.
C. The Owner will not provide electricity or compressed air for the construction of the
reservoir. The Contractor may be able to use the water from the site at the prevailing
rate to be paid to the City. The Contractor will be responsible for installation of the water
meter and temporary piping for the purpose of metering the water used during
construction.
D. This work shall be performed on a design-build basis by an independent tank fabricator /
erector (Contractor). The Contractor shall provide the foundation, steel tank, pipe
connections, man ways, ladders, hatches, vents, water level indicator, and other
appurtenances shown on the drawings and/or included in the specifications. The work to
be performed under these specifications includes, but is not limited to, the design,
fabrication, construction, cleaning, coating, painting, disinfection, and testing of welded
steel ground water storage tanks, including the foundation and all accessories as shown
and specified in the Contract Documents.
E. The tank lining and coating systems are specified in Section 13217. The hydro test and
disinfection of the tank shall conform to Section 13206.
F. The Contractor shall provide all labor, materials, equipment, tools, supervision, and
incidentals necessary to construct the water storage tanks as shown and specified in the
Contract Documents.
G. The tank shall be vertical, cylindrical, flat-bottom type of all-welded steel construction,
supported on a poured-in-place reinforced-concrete ring foundation. Height of the tank,
steel tank plate thicknesses, foundation details shown on the drawings is the minimum
requirement. The Contractor will re-evaluate the height of the tank to accommodate the
freeboard predicted by the formula in AWWA D100 latest edition using the appropriate
seismic use group as required by the soils report. Should the calculations performed by
the Contractor indicate lower tank height, lower plate thicknesses, or smaller concrete
ring foundation, the Contractor shall supply the tank with the height, plate thicknesses,
and concrete foundation as indicated in the contract documents.
H. All materials used for tank construction shall be new, previously unused and shall comply
with all the requirements of this standard. Copies of the mill test reports shall be
furnished.
1.02
PRE-QUALIFICATION OF CONTRACTOR:
A.
Bids will only be accepted from experienced Contractors who have successfully
completed at least 5 (five) tanks of equal or greater capacity in the last five (5) years.
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WELDED STEEL WATER STORAGE TANK
SECTION 13205 - WELDED STEEL WATER STORAGE TANK
Each bidder shall provide a list of at least 5 (five) such projects stating location,
completion date, contact names and telephone numbers. If a contact name and
telephone number listed cannot be reached, this project will not count as one of the five
minimum projects.
1.03
REFERENCED STANDARDS
A.
The materials, design, fabrication, erection and inspection of the welded steel tank and
foundation, shall conform to the latest editions of: ACI 301 Specifications for Structural
Concrete for Buildings; ACI 318 Building Code Requirements for Structural Concrete;
ASCE 7 Minimum Design Loads for Buildings and Other Structures; AWWA C652
Standard for Disinfection of Water Storage Facilities; AWWA D100 Standard for Welded
Steel Tanks for Water Storage; AWWA D102 Standard for Painting Steel Water Storage
Tanks; NSF 61 Drinking Water System Components; OSHA Occupational Safety and
Health Standards; SSPC-PAS Steel Structures Painting Council: Paint Application
Specification.
1.04 GEOTECHNICAL REPORT
A.
The soils investigation report furnished by a qualified Geotechnical Engineer dated
February 3, 2015 is included in Appendix A of the Project Specifications.
1.05
SUBMITTALS
A. Each Bidder shall submit with its proposal a sketch of the tank showing major dimensions
and plate thickness, nozzles and nozzle orientation, manholes, together with details of
the reinforced concrete foundation. The latter shall show preliminary dimensions and
approximate quantities of concrete and reinforcing steel.
B. Manufacturer’s qualification submittal.
C. After award and prior to construction, the successful bidder shall furnish detailed
drawings of the tank and foundation sealed by a Professional Engineer licensed in the
State of California. The successful bidder shall include a specification sheet for seismic
data per AWWA D 100 – Welded Steel Tanks for Water Storage.
D. The successful bidder shall provide details of welded joints, including the sequence and
methods for welding 3 plate intersections for floors and roofs. Mill test reports shall be
submitted for all steel materials prior to shop fabrication of plates. Steel supplied for the
tanks shall be all new.
E. The Contractor shall provide certified copies of radiography reports at the end of erection
of tanks before start of painting and coating work. The Owner will provide the services of
an independent radiograph inspector to evaluate the quality of the welding. If any weld
defect is established, the Contractor will correct the defective welding and re-radiograph
the welds to the satisfaction of the independent radiograph inspector. No additional
compensation will be provided to the Contractor for the repair of defective welding. The
cost for the independent radiograph inspector shall be by the Owner. The submitted
radiography reports shall become property of the City Engineer.
F. Welder’s certifications shall be submitted in accordance with AWWA D100 upon request.
G. Design calculations certified by a Professional Engineer proving compliance with all
requirements herein, shall be furnished by the Contractor to the Engineer.
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WELDED STEEL WATER STORAGE TANK
SECTION 13205 - WELDED STEEL WATER STORAGE TANK
H. Submittals shall conform to the requirements of Section 01300 – Contractor Submittals.
I.
After conclusion of the Work of this Section, the Contractor shall submit a written
compliance certification report per AWWA D 100, paragraph 11. The report shall include
the following:






Copy of the welder performance qualifications
Summary of inspection radiographs and inspection by air carbon arc gauging
Identification of unacceptable radiographs and inspections by arc gauging and
statement of the action taken to rectify unsatisfactory welds
Record of welders employed on each joint
Certified record of welders.
Radiographs and inspection records.
PART 2
2.01
PRODUCTS
GENERAL
A. Provide one ground storage tank as shown on the Plans and as specified in this section
and located as shown on the Plans. The approximate dimensions of the tank shall be as
follows:
Diameter: 72 feet
Sidewall Height: 22.6 feet plus the required freeboard per AWWA D100
2.02
DESIGN CRITERIA
A.
The roof shall be of “witches hat” design with a minimum slope of 1 inch in 12 inches.
B.
Dead load shall be the estimated weight of all permanent construction and fittings. The
unit weight of steel shall be considered as 490 pounds per cubic foot and the unit weight
of concrete shall be taken as 144 pounds per cubic foot.
C.
Live load shall be the weight of all of the liquid when the tank is filled to the overflow. The
unit weight of water shall be considered as 62.4 pounds per cubic foot.
D.
The specified snow load shall not be less than that required by AWWA D100 Section
3.1.3.
E.
Wind load shall be 115 miles-per-hour
F.
Seismic design shall be in accordance with AWWA D100 Section 3.1.5 for the zoning
indicated by AWWA D100 Figure 7.
G.
The design for all sections of the steel tank (cylinders, conical and double curved) shall
be per the classes of materials and unit tension/compression stresses mentioned in the
latest edition of AWWA D100.
H.
The tank details shall be designed to eliminate un-welded joints that will promote
corrosion, pockets that will accumulate rain water, and attachments to the shell which
result in excessive localized stresses due to welding or imposed loads. The exceptions
to this requirement are the roof rafters and internal roof plate lap joints. The contact
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SECTION 13205 - WELDED STEEL WATER STORAGE TANK
surfaces between the roof rafters and roof plates and the interior roof plate lap joints shall
be primed before erection in accordance with Section 09800 - Painting and Coating.
I.
Welds joining shell plates and wetted roof plates shall have complete joint penetration
and fusion and shall be double-welded from both sides. The use of low-hydrogen
electrodes is mandatory for manual welding of shell plates, for permanent attachments to
the shell plates, for fittings, and for welds joining the shell plates to the bottom plates.
Shell plates shall be rolled, regardless of material thickness.
J.
The roof shall be designed for the minimum live load and shall have a pitch as indicated.
Lateral bracing of rafter compression flanges shall not be assumed to be provided by
friction between roof sheets and rafters. Rafters and bridging between rafters shall be
designed of standard structural steel shapes. The minimum roof plate thickness shall be
3/16-inch.
K.
Columns shall be fabricated from steel pipe sealed at both ends. Column bases shall be
fabricated from steel plate and provided with the necessary gusset plates to distribute the
load uniformly. The base plates shall be designed for a maximum foundation loading of
2,000 pounds per square foot, exclusive of the weight of water. The column bases shall
not be welded to the bottom plates but shall be prevented from lateral movement by
angle clips welded to the bottom plates. Where column base plates are placed over lap
joints, filler plates shall be used to provide full bearing under the base. Structural steel
shapes shall not be used for column bases.
L.
Nuts and bolts used for erection purposes shall be hot-dip galvanized after fabrication.
Bolts inside the reservoir that support permanent loads, ladders, or appurtenances shall
be Type 304 stainless steel.
M.
The tank bottom, including sketch and annular plates, shall be fabricated from steel plate
not less than 1/4-inch thick. Annular bottom plates shall be provided per Section 13 of
AWWA D100, except that the butt-welded joints shall be double-welded from both sides.
The minimum annular plate width shall be determined by AWWA D100, Section 13.
N.
The design, materials, fabrication, construction, and inspection of the steel tank shall
conform to AWWA D100, except as modified herein.
O.
No corrosion allowance is required.
2.03
APPURTENANCES
A.
One vent of adequate size to handle a pressure differential caused by water entering or
leaving the tank at a maximum rate shall be provided. The maximum inlet rate is 2,000
gpm, the maximum withdrawal rate is 2,000 gpm. The open area of the overflow shall
not be considered as a venting area. The vent shall have stainless steel insect screens
and shall be designed to relieve any pressure or vacuum in the event the screen frosts
over or is otherwise clogged and shall be easily dismantled for cleaning. Center roof vent
shall be 48 inch minimum.
B.
Ladders, safety devices and safety cages shall be as required by state and federal
regulations. All ladders shall be furnished with "Saf-T-Climb” or equal, fall prevention
devices and shall meet OSHA standards. The City shall be supplied with 2 sleeves and 2
belts.
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SECTION 13205 - WELDED STEEL WATER STORAGE TANK
C.
One 36-inch by 36-inch steel rainproof, flanged roof hatch shall be supplied, with hinges
and hasps for locking and one 36-inch by 36-inch steel rainproof, flanged roof hatch with
removable cover, so constructed that an exhaust fan may be connected for ventilation
during painting.
D.
One 36-inch diameter shell manhole shall be supplied, equipped with hinges, centered
four feet above the base of the tank. This manhole shall have a bolting flange suitable for
connecting an exhaust fan for ventilation and a suitable blind flange and gasket.
E.
All welded joints on the tank in contact with the tank contents shall be seal welded as a
minimum.
F.
A 12-inch diameter steel inlet pipe shall be provided with the following configuration as
shown on the plans: Steel inlet pipe welded to the tank wall and flange-bolted to ductile
iron inlet pipe.
G.
One 12” diameter steel outlet pipe welded to the tank wall and flange-bolted to ductile
iron outlet pipe.
H.
A 16-inch diameter overflow equipped with an anti-vortex entrance shall be provided.
Overflow shall extend down the outside of the tank and shall terminate a minimum of 32
inches above grade.
I.
Inlet shall be equipped with a removable silt stop extending four inches above the bottom
of the tank floor.
J.
One fixed ladder shall be supplied on the exterior of the tank, and one fixed ladder shall
be supplied in the interior of the tank. Each ladder shall begin at a point even with the
tank bottom. Access to roof hatches and vents shall be provided according to the
minimum requirements versus roof slope as described in Section 5.4.3 of AWWA D100.
J.
One 36” x 48” Cleanout Door as shown on the Plans.
K.
The minimum roof plate thickness shall be 3/16 – inch
L.
The tank bottom, including sketch and annular plates shall be fabricated from steel plate
not less than ¼ - inch thick.
M.
Submerged bolts inside the tank shall be Type 304 stainless steel.
N.
Design of the access manhole in the lowest ring of the shell shall conform to API 650Welded Steel Tanks for Oil Storage, and shall be hinged as indicated.
O.
The fall protection system shall comply with OSHA.
P.
Welds joining the bottom plates shall be vacuum tested using solution film. Any
detectable leaks shall be marked and repaired by welding. Sealing shall not be
accomplished by peening. One spot radiograph shall be taken on 10 percent of the buttwelded annular plates. The inside shell-to-bottom fillet welds shall be vacuum tested
using solution film before the outside welds is made.
Q.
All seismic anchor bolts and nuts shall be Type 304 stainless steel.
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SECTION 13205 - WELDED STEEL WATER STORAGE TANK
PART 3
EXECUTION
Safety and Health Requirements: In accordance with the requirements set forth by regulatory
agencies applicable to the construction industry and in accordance with the manufacturer’s
printed instructions and appropriate technical bulletins and manual, the Contractor shall provide
and require use of personal lifesaving equipment for persons working on or about the site.
As a minimum, personal lifesaving equipment shall properly address protection of these persons
in the following categories:
(a)
(b)
(c)
(d)
(e)
(f)
Head and Face Protection
Respiratory Devices
Ventilation
Sound Levels
Illumination
Temporary Ladders and Scaffolding.
3.01
INSPECTION
A.
Mill or shop inspection reports shall be supplied in accordance with Section 11.1 of
AWWA D100.
B.
At the completion of the work a written report shall be supplied in accordance with
Section 11.2.1 of AWWA D100.
3.02
CONCRETE FOUNDATION
A.
The concrete foundation shall be constructed per the details shown on the project plans.
Concrete work shall conform to the requirements of ACI 301 “Specifications for Structural
Concrete for Buildings.”
3.03
WELDING
A.
All welders shall be qualified by ASME Section IX for the processes and positions
utilized.
B.
The Contractor shall employ the services of a welding supervisor independent of the tank
erection foreman’s jurisdiction. Performing and paying for inspection and testing of welds
shall be by the Contractor and shall be completed before the application of coating and
painting.
C.
Horizontal welding shall be inspected and tested by radiographic testing consistent with
the requirements of Section 11 of AWWA D100. Sectional segments will not be allowed.
D.
The edges or surfaces of the pieces to be joined by welding shall be prepared by flame
cutting, plasma arc cutting, arc gouging, machining, shearing, grinding or chipping and
shall be cleaned of detrimental oil, grease, scale and rust. The edges of the pieces may
have a protective coating applied to them which need not be removed before they are
welded unless specifically prohibited by the WPS.
E.
Welding procedures and welding operators shall be qualified in accordance with ASME
Section IX. All field welding may be done by the shielded metal-arc welding process, the
gas metal-arc welding process, the flux-core arc-welding process and/or the submerged
arc welding process. Shop welding may be done by the shielded metal-arc process,
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SECTION 13205 - WELDED STEEL WATER STORAGE TANK
submerged-arc welding process, gas metal-arc welding process, and/or flux-core metalarc welding process. Plates and component members of the tank shall be assembled
and welded following erection methods which result in a minimum of distortion from weld
shrinkage. The weld metal shall meet or exceed the minimum requirements for visual
inspection in AWWA D100 Section 11.4 and as set forth in the radiographic acceptance
standards of AWWA D100 Section 11.6.10. Surfaces to be welded shall be free from
loose scale, slag, heavy rust, grease, paint and all other foreign material.
F.
The Contractor shall not use an automatic welding machine for vertical welds. Vertical
welds shall be radiographed for 100 percent of their length. Welds not meeting the
acceptance criteria in AWWA D100 shall be repaired and radiographed until
requirements are met.
G.
Automatic Welding Machine: If the Contractor uses an automatic welding machine for the
horizontal welds in the tank shell, the following startup procedure shall be used. After the
first 10-feet of the first pass is welded, the Contractor shall air carbon arc gouge into the
root of the weld to allow the Engineer to visually confirm that full penetration and fusion is
attained. If full penetration and fusion have not been attained, the machine shall be
immediately corrected. The procedure shall be repeated until satisfactory welding is
achieved. Defective welding in the startup area shall be repaired.
H. Roof Welds: Welds in contact with the reservoir contents shall be spot radiographed per
AWWA D100
I.
After reinforcing plate is fitted to the shell, but before the pipe or neck fitting is inserted,
the reinforcing plate shall be seal welded to the shell at the inner and outer edges. Air
pressure shall then be applied to the space between the reinforcing plate and the shell,
and the seal welds tested with solution film.
J.
The Contractor shall use a written procedure for fitting and welding the bottom plates.
Out-of-plane distortion shall not exceed 0.75 percent of the tank radius.
K. Local deviations, such as flat spots, peaked joints, and welding distortion shall be limited
as follows for the shell plates:
(a)
(b)
(c)
Using a horizontal sweep board 36-inches long, the distance from the sweep
board to the shell shall not be greater than 1/2-inch. Flat spots shall be
measured with an external sweep board. Peaked spots shall be measured
with an internal sweep board.
Using a vertical sweep board 36-inches long, banding of horizontal joints
shall not exceed 1/2-inch.
Measurements shall be taken beginning with the first joints that are welded.
Corrections to the fitting and welding procedure shall immediately be made if
the joints are not within the distortion criteria. The Contractor shall submit
corrective procedures for joints that have been welded but are not within the
criteria for distortion.
---END OF SECTION--
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