This standard is intended to be a procurement specification to facilitate the production and procurement of storage tanks for the petroleum industry. When revisions of this standard have been issued, they may be applied to tanks to be completed after the date of issue.
GENERAL
LIMITATIONS
COMPLIANCE
A 193M/A 193 Alloy steel and stainless steel bolts for use at high temperatures. A 194M/A 194 Carbon and alloy steel nuts for front bolts. A 234M/A 234 forged carbon steel and alloy steel pipe fittings for medium and high temperature use.
SECTION 2—MATERIALS
- GENERAL
- PLATES .1 General
- ASTM Specifications
- CSA Specifications
- ISO Specifications
- National Standards
- General Requirements for Delivery
- Heat Treatment of Plates
- Impact Testing of Plates
- Toughness Requirements
- Toughness Procedure
- SHEETS
- STRUCTURAL SHAPES
- PIPING AND FORGINGS
- FLANGES
- BOLTING
- WELDING ELECTRODES
When specified by the plate purchaser, fully killed steel shall be made according to fine grain practice. If the treatment of the plates is not specified to be done at the plate producer's plant, testing must be carried out in accordance with 2.2.7.2.
SECTION 3—DESIGN
JOINTS .1 Definitions
- double-welded butt joint: A joint between two abutting parts lying in approximately the same plane that is
- single-welded butt joint with backing: A joint between two abutting parts lying in approximately the
- double-welded lap joint: A joint between two overlapping members in which the overlapped edges of both
- single-welded lap joint: A joint between two overlapping members in which the overlapped edge of one
- fillet weld: A weld of approximately triangular cross section that joins two surfaces at approximately right
- full-fillet weld: A fillet weld whose size is equal to the thickness of the thinner joined member
- tack weld: A weld made to hold the parts of a weldment in proper alignment until the final welds are made
- Weld Size
- Restrictions on Joints
- Welding Symbols
- Typical Joints .1 General
- Vertical Shell Joints
- Horizontal Shell Joints
- Lap-Welded Bottom Joints
- Butt-Welded Bottom Joints
- Bottom Annular-Plate Joints
- Shell-to-Bottom Fillet Welds
- Wind Girder Joints
- Roof and Top-Angle Joints
The use of a backing strip of at least 3 mm (1/8 inch) thick adhesive welded to the underside of the plate is permitted. For tanks with a diameter less than or equal to 9 m (30 ft) and a supported cone roof (see 3.10.4), the top edge of the shell may be flanged instead of installing a top angle .
DESIGN CONSIDERATIONS .1 Design Factors
- External Loads
- Protective Measures
- External Pressure
- Tank Capacity
At the buyer's option, the protruding leg of the top angle can extend inside or outside the tank bowl. The bend radius and width of the flange edge shall correspond to the details in Figure 3-3A.
SPECIAL CONSIDERATIONS .1 Foundation
- Corrosion Allowances
- Service Conditions
- Weld Hardness
The net working capacity is equal to the maximum capacity (3.2.5.2) less the minimum remaining working volume in the tank, less the degree (or volume) of protection against overfilling (see Appendix L).
BOTTOM PLATES
ANNULAR BOTTOM PLATES
SHELL DESIGN .1 General
- Allowable Stress
- Calculation of Thickness by the 1-Foot Method .1 The 1-foot method calculates the thicknesses
- Calculation of Thickness by the Variable- Design-Point Method
- Calculation of Thickness by Elastic Analysis For tanks where L/H is greater than 2, the selection of shell
Complete, independent calculations shall be made for all courses for the design condition, excluding any corrosion allowance, and for the hydrostatic test condition. The total thickness of the bottom layer of the shell will be used to calculate t2 (hydrostatic test).
SHELL OPENINGS .1 General
- Reinforcement and Welding
- Spacing of Welds Around Connections See Figure 3-22 for spacing requirements listed in .1
- Thermal Stress Relief
- Shell Manholes
- Shell Nozzles and Flanges
- Flush-Type Cleanout Fittings
- Flush-Type Shell Connections
The thickness (td) of the armor plate at the cleaning opening, reinforcement plate and door plate is equal to or greater than the thickness (t) of the armor plate of the lowest layer of armor. The thickness of the shell reinforcement plate must be equal to the thickness of the shell plate in the flush connection.
SHELL ATTACHMENTS AND TANK APPURTENANCES
- Shell Attachments
- Bottom Connections
- Cover Plates
- Roof Manholes
- Roof Nozzles
- Rectangular Roof Openings
- Water Drawoff Sumps
- Scaffold-Cable Support
- Threaded Connections
- Platforms, Walkways, and Stairways
The examination of the completed welds should be carried out after stress relief but before hydrostatic testing (see 6.2 and 6.5 for the appropriate inspection and repair criteria). Reinforced openings in the cover plates (or blind flanges) of shell nozzles should be limited to half the diameter of the nozzle.
TOP AND INTERMEDIATE WIND GIRDERS .1 General
- Types of Stiffening Rings
- Restrictions on Stiffening Rings
- Stiffening Rings As Walkways
- Supports For Stiffening Rings
- Top Wind Girder
- Intermediate Wind Girders
The maximum clearance between the top of the floor and the bottom of the footboard should be 6 mm (1/4 in.). The height of the middle rail should be approximately half the distance from the top of the walkway to the top of the handrail.
ROOFS .1 Definitions
- General
- Allowable Stresses .1 General
- Minimum Thicknesses
- Maximum Slenderness Ratios
- Columns
- Supported Cone Roofs
- Self-Supporting Cone Roofs
- Self-Supporting Dome and Umbrella Roofs Note: Self-supporting roofs whose roof plates are stiffened by sec-
- Top-Angle Attachment for Self-Supporting Roofs
- Tank Venting
All members in the roof-shell joint area, including the insulating rings, are considered to contribute to the cross-sectional area. When determining the allowable unit stresses, the part of the specification, "Plan of allowable stress" is used.
WIND LOAD ON TANKS (OVERTURNING STABILITY)
Tanks with both a fixed roof and a floating roof meet these requirements when they meet the circulation venting requirements of Appendix H. All other tanks designed in accordance with this standard and with a fixed roof must comply with the ventilation requirements of 3.10.8.2 and 3.10 .8.3.
SECTION 4—FABRICATION
- GENERAL .1 Workmanship
- Finish of Plate Edges
- Shaping of Shell Plates
- Marking
- Shipping
- SHOP INSPECTION
- GENERAL
- DETAILS OF WELDING .1 General
- Bottoms
- Shells
- Shell-To-Bottom Welds
- Roofs
- INSPECTION, TESTING, AND REPAIRS .1 General
- Inspection of Welds .1 Butt-Welds
- Examination and Testing of the Tank Bottom Upon completion of welding of the tank bottom, the bot-
- Inspection of Reinforcement-Plate Welds After fabrication is completed but before the tank is filled
- Testing of the Shell
- Testing of the Roof
- REPAIRS TO WELDS
- DIMENSIONAL TOLERANCES .1 General
- Plumbness
- Roundness
- Local Deviations
- Foundations
- Measurements
- RADIOGRAPHIC METHOD
- Application
- Number and Location of Radiographs .1 Except when omitted under the provisions of A.3.4,
- Technique
- Submission of Radiographs
- Radiographic Standards
- Determination of Limits of Defective Welding When a section of weld is shown by a radiograph to be
- Repair of Defective Welds
- Record of Radiographic Examination
- MAGNETIC PARTICLE EXAMINATION
- ULTRASONIC EXAMINATION
- LIQUID PENETRANT EXAMINATION
- VISUAL EXAMINATION
- VACUUM TESTING
Use of oxyfuel, electroslag or electrogas process must be done by agreement between the producer and the buyer. All repairs carried out must be subject to approval by the purchaser's inspector.
SECTION 7—WELDING PROCEDURE AND WELDER QUALIFICATIONS
- DEFINITIONS
- QUALIFICATION OF WELDING PROCEDURES .1 General Requirements
- Impact Tests
- QUALIFICATION OF WELDERS
- IDENTIFICATION OF WELDED JOINTS
- NAMEPLATES
- DIVISION OF RESPONSIBILITY
- CERTIFICATION
- Materials
- Design
- Thickness of Shell Plates
- Tank Joints
- Intermediate Wind Girders
- Shell Manholes and Nozzles
- Flush-Type Cleanout Fittings
- Flush-Type Shell Connections
- Flush-Type Bolted Door Sheets
- Raised-Type Bolted Door Sheets
When calculating these stresses, the tank diameter should be taken as the nominal downstream diameter. Note: Washers shall be used on both sides of the plate for shell thicknesses of 16 mm (5/8 in.) or less.
APPENDIX B—RECOMMENDATIONS FOR DESIGN AND CONSTRUCTION OF FOUNDATIONS FOR ABOVEGROUND OIL STORAGE TANKS
- Scope
- Subsurface Investigation and Construction
- Tank Grades
- Typical Foundation Types
- EARTH FOUNDATIONS WITHOUT A RINGWALL
- EARTH FOUNDATIONS WITH A CONCRETE RINGWALL
- EARTH FOUNDATIONS WITH A CRUSHED STONE AND GRAVEL RINGWALL
- SLAB FOUNDATIONS
- Tank Foundations for Leak Detection
The fill material must be free of vegetation, organic matter, ash and any material that could cause corrosion of the tank bottom. Placement of fill material must be in accordance with the design specification prepared by a qualified geotechnical engineer.
APPENDIX C—EXTERNAL FLOATING ROOFS C.1 Scope
Material
Design
- GENERAL
- JOINTS
- DECKS
- PONTOON DESIGN
- PONTOON OPENINGS
- COMPARTMENTS
- LADDERS
- ROOF DRAINS
- VENTS
- SUPPORTING LEGS
- ROOF MANHOLES
- CENTERING AND ANTIROTATION DEVICES
- SEALS
- GAUGING DEVICE
Adequate vents must be provided to prevent overstressing of the roof deck or insulation membrane. The length of the legs must be adjustable from the upper side of the roof.
Fabrication, Erection, Welding, Inspection, and Testing
If uncoated shoes are specified, they must be manufactured from sheet steel of the thickness and quality specified on the purchase order. The provision of such shunts shall be the subject of agreement between the purchaser and the manufacturer.
APPENDIX D—TECHNICAL INQUIRIES D.1 Introduction
Inquiry Format
APPENDIX E—SEISMIC DESIGN OF STORAGE TANKS E.1 Scope
General
Design Loading
- OVERTURNING MOMENT
ALASKA0
HAWAII
LATERAL FORCE COEFFICIENTS
The spectrum of the factor ZIC2 must correspond to the spectrum of ZIC1 modified to an attenuation coefficient of 0.5% of critical. When determining the factor ZIC1 from the spectrum, the basic period of the tank with its contents must be taken into account, unless the maximum spectral acceleration is used.
Resistance to Overturning
Where the bottom plate under the shell is thicker than the rest of the bottom, the width of the thicker plate under the shell must be equal to or greater than:.
Shell Compression
- UNANCHORED TANKS
- ANCHORED TANKS
- MAXIMUM ALLOWABLE SHELL COMPRESSION
- UPPER SHELL COURSES
The maximum longitudinal compressive stress in the tank, b/1000t (b/12t), must not exceed the maximum allowable stress, Fa, determined by the following formulas for Fa, which take into account the effect of internal pressure due to liquid content. If the thickness of the lower shell layer calculated for resistance to seismic overturning moment is greater than the thickness required for hydrostatic pressure, both without any corrosion allowances, then the calculated thickness of each upper shell layer for hydrostatic pressure shall be increased in the same proportion , unless a special analysis is made to determine the seismic overturning moment and corresponding stresses at the base of each upper shell layer.
Anchorage of Tanks
- MINIMUM ANCHORAGE
The maximum allowable design stress in the shell at anchor attachment shall be limited to 170 MPa (25,000 psi) with no increase for seismic loading. The supplied anchors, including their corrosion allowance, are used to determine the design loads for the shell attachment and installation requirements.
Piping
These stresses may be used in conjunction with other loads for seismic loading when the combined load is dominant.
Additional Considerations
Overturn stability with respect to wind conditions shall be determined in accordance with 3.11, if specified by the purchaser. The overturning stability with respect to seismic conditions must be determined independently of the internal pressure increase.
Venting (Deleted) F.3 Roof Details
This appendix applies to the storage of non-refrigerated liquids (see also API Standard 620, Annexes Q and R).
Maximum Design Pressure and Test Procedure
W = total weight of the shell and any frame (but not roof panels) supported by the shell and roof (N), M = wind moment (N-m), when the wind changes. W = total weight of the shell and any frame (but not roof panels) supported by the shell and roof (lbf), M = wind moment (ft-lbf), when the wind changes.
Required Compression Area at the Roof-to-Shell Junction
Anchoring may be required when the maximum design pressure is combined with the specified load. If overturning stability is not specified, the manufacturer must report the maximum wind speed that the tank can withstand without anchoring when combined with the maximum design pressure.
Calculated Failure Pressure
The air pressure shall then be reduced to half the design pressure and all welded joints above the liquid level shall be checked for leakage by means of a film of soap, linseed oil or other suitable material. Experience with actual failures indicates that buckling of the roof-to-shell junction is localized and probably occurs when the yield point of the material is exceeded in the area of the compression ring.
Anchored Tanks with Design
- PURPOSE
- DEFINITION
- GENERAL APPLICATION .1 New Tanks
- Existing Tanks
- Existing Tank Data Sheet
- SPECIAL FEATURES .1 Self-Supporting Structure
- Finish
- Maintenance and Inspection
When specifying this attachment for a new tank, the tank must be designed to support the aluminum dome roof. Unless otherwise specified, any reinforcement required to enable the tank to support the roof will be the responsibility of the purchaser.
Materials
- GENERAL
- STRUCTURAL FRAME
- ROOF PANELS
- BOLTS AND FASTENERS
- SEALANT AND GASKET MATERIAL
- SKYLIGHT PANELS
The upper part of the tank housing must be structurally suitable for fixing the dome roof structure. When an aluminum dome is ordered for an existing tank, the customer must complete a data sheet (see Figure G-1).
Allowable Stresses
- ALUMINUM STRUCTURAL MEMBERS Aluminum structural members and connections shall be
- ALUMINUM PANELS
- BOLTS AND FASTENERS
Fasteners shall be 7075-T73 aluminum, 2024-T4 aluminum, austenitic stainless steel or other materials as agreed to by the purchaser. Skylight panels shall be clear acrylic or polycarbonate with a minimum nominal thickness of 6 mm (0.25 in).
Design
- DESIGN PRINCIPLES
- DESIGN LOADS .1 Dead Load
- Live Load
- Wind Load
- Seismic Load
- Load Combinations
- Panel Loads
- INTERNAL PRESSURE
The dead load is the weight of the roof and all accessories permanently attached to it, including any insulation. The minimum live load shall be a uniform load of 1.2 kPa (25 lbf/ft2) of projected area.
Roof Attachment
- LOAD TRANSFER
- ROOF SUPPORTS
- SEPARATION OF CARBON STEEL AND ALUMINUM
- ELECTRICAL GROUNDING
If an internal or external design pressure is specified by the purchaser, the loads resulting from one of these pressures shall be added to the load combinations specified in Sec. a–g above and the structure must be designed for the most severe load. When the design pressure, Pmax, for a tank with an aluminum domed roof is to be calculated, the weight of the roof including construction is added to the weight of the shell in the W joint in F.4.2, and th is taken as zero.
Physical Characteristics
- SIZES
- DOME RADIUS
Unless otherwise specified by the purchaser, the internal design pressure must not exceed the weight of the roof.
Platforms, Walkways, and Handrails
Appurtenances
- ROOF HATCHES
- ROOF NOZZLES AND GAUGE HATCHES Roof nozzles and gauge hatches shall be flanged at the base
- ROOF VENTS
Sealing at the Shell
Testing
- LEAK TESTING
Fabrication and Erection
- GENERAL
- FABRICATION
- WELDING
- SHIPPING AND HANDLING
- ERECTION
- WORKMANSHIP
This annex provides minimum requirements applicable to a tank with an internal floating roof and a fixed roof at the top of the tank shell, and for the tank fittings. The requirements apply to the internal floating roof of a new tank and can be applied to an existing fixed roof tank.
Types
This appendix is only intended to limit the factors that affect the safety and durability of the installation and which are considered to be in accordance with the quality and safety requirements of this standard. Types of internal floating roofs (listed under H.2) and materials (listed under H.3) are given as a basic guide and shall not be deemed to limit the purchaser's ability to use other generally accepted or alternative designs as long as all design loads is documented to meet the minimum requirements herein and all other criteria are met (except alternative materials and thicknesses as permitted by H.3.1).
Material
- STEEL
- ALUMINUM
- STAINLESS STEEL
Material must be certified to meet all the requirements of a material specification listed in this appendix and approved by the purchaser or must comply with requirements as specified by the purchaser. When specified by the purchaser, a corrosion allowance shall be added to the minimum nominal thickness specified below.
Requirements for All Types
- GENERAL
- INTERNAL FLOATING ROOF DESIGN .1 All internal floating roof design calculations shall
- JOINT DESIGN
- PERIPHERAL SEALS
- Seal Types
- ROOF PENETRATIONS
- ROOF SUPPORTS
All calculations for the floating condition must be based on the design specific gravity (as per H.4.2.1). For other steel components, the allowable stress and stability requirements must be jointly determined by the purchaser and manufacturer as part of the inquiry.
Openings and Appurtenances
- LADDER
- VENTS
- Internal Floating Roof Pressure-Vacuum (Bleeder) Vents
- Tank Circulation Vents
- LIQUID-LEVEL INDICATION AND OVERFLOW SLOTS
- ANTIROTATION AND CENTERING DEVICES The internal floating roof shall be centered and restrained
- MANHOLES AND INSPECTION HATCHES .1 Fixed-Roof Manholes
- Floating-Roof Manholes
- Inspection Hatches
- INLET DIFFUSER
- GAUGING AND SAMPLING DEVICES
- CORROSION GAUGE
When specified by the purchaser, the fixed roof and internal floating roof shall be equipped with and/or measuring and sampling equipment. When specified by the purchaser, a corrosion gauge for the internal floating roof shall be provided adjacent to the scale to indicate the overall rate of corrosion.
Fabrication, Erection, Welding, Inspection, and Testing
When specified by the purchaser, inspection hatches shall be fitted to the fixed roof to permit visual inspection of the seal area. The peripheral assembly must be checked for proper operation throughout the entire travel of the internal floating roof.
APPENDIX I—UNDERTANK LEAK DETECTION AND SUBGRADE PROTECTION I.1 Scope and Background
- Performance Requirements
- Cathodic Protection
- Double Steel Bottom Construction
- Material Requirements and Construction Details
- Testing and Inspection
- Tanks Supported by Grillage
- Typical Installations
The tank owner should be presented with the manufacturer and full description of the leak barrier material. The owner of the tank and the manufacturer agree on the required strength and flexibility of the lining seams.
APPENDIX J—SHOP-ASSEMBLED STORAGE TANKS J.1 Scope
- Materials
- Design
- JOINTS
- BOTTOMS
- SHELLS
- WIND GIRDERS FOR OPEN-TOP TANKS Open-top tanks shall be provided with wind girders as
- ROOFS .1 General
- TANK CONNECTIONS AND APPURTENANCES
- CORROSION ALLOWANCE
- LIFTING LUGS
- ANCHORING
- Fabrication and Construction
- GENERAL
- TESTING, REPAIRS, AND INSPECTION .1 General
- Inspection of Shell Joints
- Welding Procedure and Welder Qualifications
- Marking
The location of the buttons shall be agreed upon by the purchaser and the manufacturer. Shop-assembled tanks must be marked in accordance with Article 8, except that 8.1.4 and 8.2 do not apply.
APPENDIX K—SAMPLE APPLICATION OF THE VARIABLE- DESIGN-POINT METHOD TO DETERMINE SHELL-PLATE THICKNESS
Calculations
- FIRST COURSE ( t 1 )
- SECOND COURSE ( t 2 ) In SI units
- UPPER COURSES .1 Course 2
- First Trial In SI units
- Second Trial In SI units
- Third Trial In SI units
- Course 3 Note: H = 14.4 m (48 ft)
The following data sheets shall be used by the purchaser when ordering and by the manufacturer when bidding for a storage tank constructed in accordance with this standard. Upon completion of construction, the manufacturer shall provide the purchaser with a copy of the data sheets corrected to reflect the as-built conditions.
Scope
Thermal Effects
Modifications in Stress and Thickness
The thickness of the lower reinforcement plate, bolt flange and cover plate shall be multiplied by the ratio of 205 MPa (30,000 psi) to the yield strength of the material at maximum operating temperature if the ratio is greater than unity.
Tank Bottoms
Sy = specified minimum yield strength of the bottom plate at the maximum operating temperature of the tank (MPa), D = nominal diameter of the tank (m). Sy= specified minimum yield strength of bottom plate at maximum tank operating temperature (lbf/in.2).
Self-Supporting Roofs
When the equation for S is used, the shell thickness t must be greater than or equal to the ring plate thickness tb,. The actual design value of C must be determined taking into account the operating and heating procedure of the tank and heat transfer to the subsurface (see footnote 16).
Wind Girders
APPENDIX N—USE OF NEW MATERIALS THAT ARE NOT IDENTIFIED N.1 General
Conditions
APPENDIX O—RECOMMENDATIONS FOR UNDER-BOTTOM CONNECTIONS O.1 Scope
Recommendations
Guideline Examples
- CONCRETE VAULT AND RINGWALL (SEE FIGURES O-1 AND O-2)
