12F e12 fm Specification for Shop Welded Tanks for Storage of Production Liquids API SPECIFICATION 12F TWELFTH EDITION, OCTOBER 2008 EFFECTIVE DATE APRIL 1, 2009 Specification for Shop Welded Tanks fo[.]
General
This specification outlines the requirements for the material, design, fabrication, and testing of shop-fabricated vertical cylindrical welded steel storage tanks These tanks are designed for aboveground use and come in various standard sizes and capacities, suitable for internal pressures that are approximately atmospheric and do not exceed the limits specified in Table 1, Column 2.
This specification aims to ensure that the oil production industry has access to safe and cost-effective tanks for storing crude petroleum and other commonly handled liquids It serves as a guide for both purchasers and manufacturers in the ordering and fabrication of these tanks.
Compliance
The manufacturer must adhere to all provisions of this specification, and the purchaser has the right to conduct investigations to ensure compliance Any materials that do not meet the specification may be rejected It is recommended that the purchaser exercise this right and perform independent inspections, in addition to any provided by the manufacturer The purchaser's inspector should closely monitor all aspects of shop fabrication, field construction, and testing that impact the integrity and safety of the final structure.
API Specification 5L, Specification for Line Pipe
API Standard 2000, Venting Atmospheric and Low-Pressure Storage Tanks: Nonrefrigerated and Refrigerated
ASME B1.1 1 , Unified Inch Screw Threads (UN and UNR Thread Form)
ASME B16.5, Pipe Flanges and Flanged Fittings
ASME B16.11, Forged Steel Fittings, Socket-Welding and Threaded
ASME B18.2.1, Square and Hex Bolts and Screws, Inch Series
ASME B18.2.2, Square and Hex Nuts
ASME Boiler and Pressure Vessel Code, Section IX—Welding and Brazing Qualifications
ASTM A36 2 , Standard Specification for Carbon Structural Steel
ASTM A53, Standard Specification for Pipe, Steel, Black and Hot-Dipped, Zinc-Coated, Welded and Seamless
ASTM A106, Standard Specification for Seamless Carbon Steel Pipe for High-Temperature Service
1 ASME International, 3 Park Avenue, New York, New York 10016, www.asme.org.
2 ASTM International, 100 Barr Harbor Drive, West Conshohocken, Pennsylvania 19428, www.astm.org.
ASTM A153, Standard Specification for Zinc Coating (Hot-Dip) on Iron and Steel Hardware
ASTM A283, Low and Intermediate Tensile Strength Carbon Steel Plates of Structural Quality
ASTM A285, Standard Specification for Pressure Vessel Plates, Carbon Steel, Low- and Intermediate-Tensile
ASTM A307, Standard Specification for Carbon Steel Bolts and Studs, 60,000 PSI Tensile Strength
ASTM A1011, Standard Specification for Steel, Sheet and Strip, Hot-Rolled, Carbon, Structural, High- Strength Low-
Alloy, High-Strength Low-Alloy with Improved Formability, and Ultra-High Strength
ASTM B454, Specification for Mechanically Deposited Coatings/Cadmium/Zinc on Ferrous Metal
AWS A 5.1 3 , Specification for Carbon Steel Electrodes for Shielded Metal Arc Welding
NFPA No 30 4 , Flammable and Combustible Liquids Code
A weld placed in a groove between abutting members Grooves may be square, V (single or double), or U (single or double).
A joint between two abutting parts lying in approximately the same plane and welded from both sides
A joint that incorporates filler metal from just one side is regarded as equivalent to a double-welded butt joint, provided that methods are in place to ensure full penetration and reinforcement on both sides of the joint.
A joint between two overlapping members in which the overlapped edges of both members are welded with fillet welds
A weld of approximately triangular cross-section joining two surfaces approximately at right angles to each other, as in a lap joint, tee joint, or corner joint.
A fillet weld whose size is equal to the thickness of the thinner member joined.
A weld made to hold parts of a weldment in proper alignment until the final welds are made.
3 American Welding Society, 550 N.W LeJeune Road, Miami, Florida 33126, www.aws.org.
4 National Fire Protection Association, 1 Batterymarch Park, Quincy, Massachusetts 02169-7471, www.nfpa.org.
S PECIFICATION FOR S HOP W ELDED T ANKS FOR S TORAGE OF P RODUCTION L IQUIDS 3
General
The materials specified in this section are chosen to ensure sufficient strength and a satisfactory service life Alternative materials with equal or superior mechanical properties may be utilized upon mutual agreement between the purchaser and the manufacturer However, if higher strength materials are employed, the minimum thickness requirements outlined in this specification must be maintained.
Plates
Plates shall conform to the latest edition of one of the following ASTM standards: ASTM A36, ASTM A283 (Grade C or D), and ASTM A285 (Grade C).
Shell plates with established minimum thicknesses, which exceed computed requirements by practical considerations and do not fall below the computed thickness by more than 0.01 inches, along with all roof and bottom plates, can be acquired based on weight The specified plate thicknesses and weights are minimums; purchasers may request thicker or heavier materials at their discretion.
Sheets
Sheets must meet the latest ASTM A1011 standards, specifically Grade C or D, produced through either the open-hearth or basic oxygen processes Tank manufacturers have the option to order sheets based on weight or thickness.
Welding Electrodes
Manual arc-welding electrodes must meet the E60 and E70 Series Classification standards, which are designed for specific electric current characteristics, welding positions, and other intended use conditions, as outlined in the latest edition of AWS A 5.1.
Structural Shapes
Structural shapes shall be of open-hearth, electric-furnace, or basic oxygen process and shall conform to the latest edition of ASTM A36.
Piping
Pipe shall conform to Grade A or B of the latest edition of API 5L, ASTM A53, or ASTM A106.
Flanges
Hub slip-on welding and welding-neck flanges shall conform to the material requirements for forged carbon steel flanges as specified in ASME B16.5.
Couplings
Couplings for threaded connections can be provided with or without recesses, meeting the dimensional, physical, and chemical standards outlined in the latest edition of API 5L, Grade B Additionally, these couplings may also adhere to the most recent edition of ASME B16.11.
Bolting
Tank bolting with a diameter of 1/2 inch and a length of 1/2 inch must meet the requirements outlined in Annex A All other bolting should comply with the latest revision of ASTM A307, Grade A or B Unless specified otherwise in the purchase order, black-finish bolts and nuts will be provided If galvanized bolts and nuts are required, they must be zinc-coated according to Annex A or the relevant ASTM specification Alternative materials or finishes that adhere to recognized bolting standards may be supplied upon agreement between the purchaser and the manufacturer.
General
Tanks adhering to this specification are engineered based on established calculations to determine the minimum metal thickness and bolting requirements for various sizes when filled with water at a density of 62.37 lb/ft³ at 60°F, along with the internal pressure outlined in Table 1, Column 2 To ensure structural stability and integrity, extra metal thickness is incorporated beyond the calculated minimum It is imperative that the minimum metal thickness specified in this standard is never reduced.
Joint Design Definitions
Definitions in Section 3 shall apply to tank-joint designs.
Size of Weld
The size of a weld is determined by specific dimensions: for groove welds, it is based on the joint penetration, which includes the depth of chamfering and the specified root penetration In the case of fillet welds, equal leg fillet welds are measured by the leg length of the largest inscribed isosceles right triangle within the fillet-weld cross-section, while unequal leg fillet welds are defined by the leg lengths of the largest inscribed right triangle within the same cross-section.
Joint Restrictions
The article outlines specific restrictions regarding the type and size of joints or welds in construction It states that tack welds are not to be considered as having any structural strength For fillet welds, the minimum size requirements are established: for plates with a thickness of 3/16 inches, full-fillet welds are required, while for thicker plates, the weld size must be at least one-third the thickness of the thinner plate at the joint, with a minimum of 3/16 inches Additionally, single-welded joints are prohibited on tank bottoms, shells, or decks.
Size
Tanks under this specification shall be furnished in the sizes and dimensions as stipulated in Table 1, Column 1 through Column 7, and Figure 1, as specified on the purchase order.
Bottom Type Design
The tank bottom must be either flat or designed as Type A (unskirted) or Type B (skirted), as indicated in the purchase order Both Type A and Type B cone bottoms should adhere to the specifications outlined in Figure 2 and Figure 3, respectively.
S PECIFICATION FOR S HOP W ELDED T ANKS FOR S TORAGE OF P RODUCTION L IQUIDS 5
Thickness
The thickness of bottom plates shall be 1 / 4 in (10.20 lb/ft 2 ) nominal, except the sump of the Type A cone bottom which shall be 3 / 8 in (15.30 lb/ft 2 ) nominal.
Joints in Bottom Plates
Bottom joints shall be double-welded butt joints with complete penetration.
Shell Attachments
The tank bottom must be securely connected to the tank shell If the bottom features a flange, it should be joined using a double-welded butt joint with complete penetration or a double-welded full-fillet lap joint In cases where the bottom is not flanged, full-fillet welds are required on both the inside and outside.
Shell Thickness Design
Shell plates must have a thickness of either 3/16 in (7.65 lb/ft²) or 1/4 in (10.20 lb/ft²), as specified in the purchase order The manufacturer will determine the width of the shell plates, which should ideally be no less than 60 in.
Table 1—Tank Dimensions (See Figure 1)
Design Pressure oz/in 2 Approximate
Working Capacity (See Note) bbl
Height of Overflow Connection ft, in.
Height of Walkway Lugs ft, in.
Location of Fill-line Connection a in E
Tolerance (all sizes) ± 1 / 8 in ± 3 / 8 in ± 1 / 8 in ± 1 / 8 in ± 1 / 8 in.
NOTE The approximate working capacities shown in Column 3 apply to flat-bottom tanks.
Type A (unskirted) cone-bottom tanks offer an additional 6 inches of working height compared to flat-bottom tanks This height increase translates to an approximate capacity boost of 4 bbl for 7-ft, 11-in diameter tanks, 6 bbl for 9-ft, 6-in diameter tanks, 7 bbl for 10-ft diameter tanks, 8 bbl for 11-ft diameter tanks, 10 bbl for 12-ft diameter tanks, and 17 bbl for 15-ft, 6-in diameter tanks.
Type B (skirted) cone-bottom tanks have a working height that is 8 inches shorter than their flat-bottom counterparts, resulting in a capacity reduction of 6 bbl for 7-ft, 11-in diameter tanks, 8 bbl for 9-ft, 6-in diameter tanks, 9 bbl for 10-ft diameter tanks, 11 bbl for 11-ft diameter tanks, 13 bbl for 12-ft diameter tanks, and 15 bbl for 15-ft, 6-in diameter tanks Additionally, when specified in the purchase order, tanks can be designed for viscous oil service, which requires that dimension C of the overflow-line connections be 6 inches less than indicated in Column 6, Table 1, and dimension E of the fill-line connection be adjusted to 6 inches, with a tolerance of ± 1/8 inch.
Figure 1—Tank Dimensions—See Table 1
DETAIL OF WALKWAY BRACKET LUGS
S PECIFICATION FOR S HOP W ELDED T ANKS FOR S TORAGE OF P RODUCTION L IQUIDS 7
Shell Joints
Shell-plate joints shall be double-welded butt joints with complete penetration.
Deck Type Design
The deck shall be of the self-supporting, cone type, with a slope of 1 in in 12 in.
Thickness
The thickness of deck plates must match the thickness of shell plates; however, for tanks with a diameter of 15 ft, 6 in., the deck thickness should be a nominal 1/4 inch unless additional structural supports, such as rafters, are installed.
Deck Joints
Deck plate joints shall be double-welded butt joints with complete penetration.
Figure 2—Type A (Unskirted) Cone Bottom
Figure 3—Type B (Skirted) Cone Bottom
Shell Attachment
The tank deck must be securely connected to the tank shell If the deck is flanged, it should be attached using a double-welded butt joint with complete penetration or a double-welded, full-fillet lap joint If the deck is not flanged, full-fillet welds are required on both the inside and outside.
Cleanout Design
Tanks must include a 24-in × 36-in extended-neck cleanout, positioned as indicated in Figure 1 and adhering to the specifications in Figure 4 The cleanout cover plates should be constructed as a single piece, unless a two-piece design is requested in the purchase order, which will feature a horizontal lap seam secured with one row of 1/2-in bolts on 2-in centers, along with appropriate gaskets and bolt retainers If a two-piece construction is chosen, the top inspection plate should provide a clear opening of approximately 14 in × 24 in., unless otherwise specified Additionally, if requested, handles for lifting the cleanout cover plate(s) will be included.
Connections Design8
Tanks are equipped with inlet and outlet connections as detailed in Table 1 and Figure 1 Unless specified otherwise, these connections will be full couplings, welded with full-fillet welds on both the inside and outside surfaces, ensuring equal projections Half couplings may be used for specific connections (C-1, C-4, C-5, and C-6) at the manufacturer's discretion Additional connections of varying sizes or locations can be arranged through agreement between the purchaser and manufacturer For flanged or alternative connections, the nozzle neck must be a minimum of standard weight pipe, also attached with full-fillet welds on both sides The bolting pattern for the thief hatch must adhere to the specifications in Figure 1.
Anti-channel Drain Baffle Design
An anti-channel drain baffle must be provided as specified in the purchase order, featuring a periphery of 64 inches in plan view The baffle height should be a minimum of 4 inches for 90-bbl tanks and 5 1/4 inches for all other sizes, with spacers ensuring the bottom edge is 1 inch above the tank bottom A drain line, sized at 3 inches nominal for 90-bbl tanks and 4 inches nominal for other sizes, must connect the baffle to the tank shell The baffle should be secured to the tank bottom using a J-bolt through an eye retainer welded to the tank bottom, without any welding of the baffle to the tank bottom.
Downcomer Pipe
A downcomer pipe shall be installed if requested by the purchaser; design of downcomer to be by agreement between purchaser and manufacturer.
S PECIFICATION FOR S HOP W ELDED T ANKS FOR S TORAGE OF P RODUCTION L IQUIDS 9
Normal Venting
Connections C-1 and C-3 facilitate normal inbreathing and outbreathing in response to temperature fluctuations and liquid movement in and out of the tank It is essential to equip these connections with appropriately sized pressure-vacuum valves, following the guidelines of API 2000 The pressure setting for these valves should be between 2 oz/in² and 4 oz/in² lower than the opening pressure of emergency venting devices For assistance in selecting the appropriate venting devices, refer to Annex B.
Emergency Venting
When storage tanks with flammable liquids face fire exposure, the venting rate can exceed normal thermal effects and oil movement To ensure safety, especially in non-remote locations, purchasers must provide pressure relieving devices that offer additional capacity beyond standard venting, as specified in Table C.1 Importantly, the opening pressure of these devices must not surpass the tank's design pressure.
Figure 4—24-in × 36-in Extended-neck Cleanout (See 5.16)
1” under relieving conditions should not exceed that tabulated in Table C.1, Column 6 Pressure relieving devices may take the form of larger or additional vent valves or additional thief hatches.
NOTE With drainage as used in Table C.1, Column 5 means that flammable or combustible liquids will not be retained near the tank by dykes or firewalls.
Fabrication
Fabrication shall be completed in the shop of the manufacturer in accordance with the best modern practices.
Welding
Welding procedures must be established, and welding operators should be qualified by the manufacturer The qualification of welders must adhere to the relevant sections of the latest edition of Section IX of the ASME Boiler and Pressure Vessel Code.
Testing
Tanks must undergo testing at the manufacturer's shop using a specific method: first, brace the bottom by securely attaching an external stiffening member to prevent permanent deformation during the test Next, close all openings with appropriate plugs or covers, utilizing bolts and gaskets that match the final installation requirements Finally, the tank will be tested with air at 1.5 times the maximum design pressure.
When conducting air tests, it is essential to utilize appropriate valves, regulators, and pressure relief devices to avoid overpressure and potential deformation For leak detection, apply soap suds, linseed oil, or other suitable materials to all welds on the shell, bottom, roof, and attachments, and inspect carefully for any leaks Any defects identified in the welds during the leak test must be repaired by the manufacturer, followed by a retest of the tank After releasing the air pressure, any bottom stiffening used should be removed, and any resulting scars must be repaired.
External Painting
Prior to shipment, it is essential to clean tanks of rust, grease, scale, and weld spatter, and to apply a high-quality commercial metal primer, unless the purchaser requests them to remain unpainted Additionally, finish coats or other protective coatings will be applied if mutually agreed upon by the purchaser and the manufacturer.
Internal Coating
When internal coating is required, procedures, and methods outlined in NACE RP 0372, Method for Lining Lease
Production Tanks with Coal Tar Epoxy are recommended as a minimum requirement Other coatings and methods may be used by agreement between purchaser and manufacturer.
S PECIFICATION FOR S HOP W ELDED T ANKS FOR S TORAGE OF P RODUCTION L IQUIDS 11
Tanks manufactured in conformance with this specification shall be identified by a nameplate bearing the information shown in Figure 5.
The nameplate must be permanently affixed to a corrosion-resistant material, either stamped, etched, or embossed, and attached to a ferrous backing plate or bracket Additionally, the nameplate information can be die stamped onto a steel plate It is essential that the bracket, backing plate, or nameplate is seal-welded to the tank shell at the specified location in Figure 1.
Inspection Notice
The purchaser's inspector must be given reasonable notice regarding the timing of inspections for purchased tanks or any designated tests to be witnessed.
Inspection by Purchaser
The purchaser's inspector shall have unrestricted access to the manufacturer's facilities during the contract work to ensure compliance with specifications The manufacturer is required to provide reasonable assistance to the inspector at no cost, facilitating the verification of material production Inspections must occur at the manufacturing site before shipment, unless stated otherwise in the purchase order, and should be conducted in a manner that minimizes disruption to the manufacturer's operations.
Rejection
Materials exhibiting harmful defects during initial inspection or after acceptance at the manufacturer's facility, or those that prove defective when used correctly, may be rejected, and the manufacturer will be informed If destructive testing is conducted outside the manufacturing site, the purchaser is responsible for payment of materials that meet the specifications, but will not pay for any materials that do not comply.
Manufactured in Accordance with API Specification 12F Manufacturer
Design Pressure _ozNominal Capacity _bbl
Compliance
The manufacturer is obligated to adhere to all aspects of this specification The purchaser reserves the right to conduct any necessary investigations to ensure the manufacturer's compliance and may reject any materials that fail to meet these specifications.
The annex addresses tank bolting with diameters ranging from 1/2 inch to 1 1/2 inches in length It specifies that bolts and nuts must be either black-finish or galvanized, as outlined in the purchase order.
The breaking load of the bolts, tested in full size, shall not be less than 11,350 lb.
The breaking load of 11,350 lb corresponds to a tensile strength of 80,000 lb/in² when calculated using the mean thread area, and it is approximately 91,000 lb/in² based on the root thread area.
Tension tests for bolts must be conducted on the completed bolt, applying the load between the head and a nut or appropriate fixture that ensures adequate thread engagement to achieve the bolt's full strength It is essential to assemble the nut or fixture on the bolt while leaving a minimum of three full threads exposed within the grip If the test fails due to thread stripping before achieving the minimum required tensile load, that specific test result should be disregarded.
The nuts for bolts shall be capable of developing the load specified in A.2 without stripping.
During the tension test specified in A.3, failure shall occur in the threaded section and not at the junction of the head and shank.
The specifications require that continuous production for stock includes sample inspections by the manufacturer to ensure that the material remains within specified limits Consequently, additional tests on individual shipments are not anticipated However, if requested in the order, one tension test must be conducted for each lot, which consists of 5,000 pieces or a fraction thereof.
Should the sample from the lot fail to meet the requirements of a specified test, two additional samples shall be tested; in which case, both samples shall meet the test.
Unplated products must feature coarse-thread series according to ANSI B1.1 standards, with bolts adhering to Class 2A tolerance and nuts to Class 2B tolerance For galvanized bolts, Class 2A threads are required prior to hot dip or mechanical galvanizing Post-galvanization, the pitch and major diameter may exceed the Class 2A limits by up to 0.021 inches.
Bolts are typically square unless the purchaser and manufacturer agree on regular hex bolts All bolts must adhere to the relevant section of the latest ANSI B18.2.1 standard.
Square and Hex Bolts and Screws.
Nuts must be square unless otherwise specified by the purchaser and manufacturer, in which case hexagonal nuts may be used All bolts must adhere to the relevant section of the most recent ANSI B18.2.2 standards.
Galvanized bolts and nuts must be hot-dip galvanized according to ASTM A153, with the coating weight specified for Class C materials After galvanizing, the nuts should be tapped If the purchaser requests mechanical galvanization, bolts and nuts must be mechanically zinc-coated, meeting the standards of Class 50 of ASTM B454 or the requirements for Class C of ASTM A153 regarding coating thickness, adherence, and quality Additionally, mechanically zinc-coated nuts intended for use with mechanically zinc-coated bolts should be tapped oversize before coating and do not require retapping afterward.
Bolt heads shall be marked (by raised or depressed mark at the option of the manufacturer) to identify the manufacturer The manufacturer may use additional marking for internal use.
Recommended Practice for Normal Venting
Table B-1—Venting Capacity Requirements (See 6.1)
Tank Size Design Pressure oz/in 2 Surface
Diameter ft, in Height ft Pressure, Vacuum Flash Point
NOTE 1 Filling and emptying venting.
— Outbreathing at maximum filling rate: For flash points less than 100°F, provide 1200 standard cubic feet per hour
(SCFH) for each 100 bbl/hr For flash points of 100°F or more, provide 600 SCFH for each 100 bbl/hr.
— Inbreathing at maximum emptying rate: For all liquids, provide 600 SCFH for each 100 bbl/hr.
NOTE 2 The values calculated for filling and emptying venting requirements shall be added to the appropriate thermal venting requirements.
Table C.1—Emergency Venting Requirements (See 6.2)
Design Pressure oz/in 2 Exposed
Max Press During Emergency Venting
Normal vents, as outlined in sections 6.1 and Annex B, can fulfill some or all of the necessary requirements When implementing the suggested emergency venting in conjunction with drainage, it is crucial to adhere to the guidelines specified in sections 2.3.2 and 2.5.7 of NFPA No 30.
Table C.2—Calculated Venting Capacity of 8-in Round Thief Hatch
NOTE Values in the above table are based on the following equation:
Q is the venting capacity in standard cubic feet of free air per hour (SCFH);
A is the hatch area in 2 (A = 44 in 2 for 8-in round hatch);
P t is the absolute pressure inside the tank in inches of water;
P a is the absolute pressure outside the tank in inches of water.
Walkways and stairways built according to this specification will utilize prefabricated components that are intended for on-site assembly next to tanks or similar structures All materials must adhere to the relevant sections outlined in Section 4.
Walkways, platforms, and stairways or ladders are designed to facilitate access to devices located on or near the deck, rather than for employee egress onto the deck itself When access to the deck is necessary, it is essential to install appropriate guard railings to prevent falls and ensure safety.
The walkway must be constructed with tread sections, railing assemblies, and toeboards that collectively support a uniform load of 50 lb/ft² or a concentrated load of 1,000 lb at any point along the span, ensuring deflection does not exceed 1/360 of the unsupported span length The maximum distance between tank brackets or ground supports is limited to 25 ft, and if intermediate supports are necessary, vertical members should end at the top rail Additionally, ground supports must be anchored to a concrete or other suitable permanent foundation.
The treadway must have a minimum width of 26 inches and feature a uniformly perforated non-skid surface created by shaped punches Additionally, at the purchaser's request, the treadway sections can be made from structural expanded metal or grating to prevent snow or ice accumulation.
Railings must include posts, horizontal braces, sway braces, gusset plates, toeboards, midrails, and a top rail The top rail should be positioned 42 inches above the treadway, and the entire structure must be able to support a concentrated force of 200 pounds applied in any direction at any point on the top rail.
Toeboards shall be installed on all open sides (except at the entrance of stairways or ladders) to provide an installed height of 4 in above the treadway.
Midrail shall be installed approximately halfway between treadway and top rail Where the midrail projects into a walkway area, the ends shall be formed to a smooth contour.