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2011 Edition, June 2007

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Welded Tanks for Oil Storage

Includes all amendments and changes through Addendum 3, August 2011

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Product Details:

  • Revision: 2011 Edition, June 2007
  • Published Date: August 2011
  • Status: Historical
  • Document Language: English
  • Published By: American Petroleum Institute (API)
  • Page Count: 450
  • ANSI Approved: No
  • DoD Adopted: Yes

Description / Abstract:


This Standard establishes minimum requirements for material, design, fabrication, erection, and testing for vertical, cylindrical, aboveground, closed- and open-top, welded storage tanks in various sizes and capacities for internal pressures approximating atmospheric pressure (internal pressures not exceeding the weight of the roof plates), but a higher internal pressure is permitted when additional requirements are met . This Standard applies only to tanks whose entire bottom is uniformly supported and to tanks in non-refrigerated service that have a maximum design temperature of 93°C (200°F) or less .

• This Standard is designed to provide industry with tanks of adequate safety and reasonable economy for use in the storage of petroleum, petroleum products, and other liquid products. This Standard does not present or establish a fixed series of allowable tank sizes; instead, it is intended to permit the Purchaser to select whatever size tank may best meet his needs. This Standard is intended to help Purchasers and Manufacturers in ordering, fabricating, and erecting tanks; it is not intended to prohibit Purchasers and Manufacturers from purchasing or fabricating tanks that meet specifications other than those contained in this Standard.

Note: A bullet (•) at the beginning of a paragraph indicates that there is an expressed decision or action required of the Purchaser. The Purchaser's responsibility is not limited to these decisions or actions alone. When such decisions and actions are taken, they are to be specified in documents such as requisitions, change orders, data sheets, and drawings.

• This Standard has requirements given in two alternate systems of units. The Manufacturer shall comply with either:

1. all of the requirements given in this Standard in SI units, or

2. all of the requirements given in this Standard in US Customary units.

The selection of which set of requirements (SI or US Customary) to apply shall be a matter of mutual agreement between the Manufacturer and Purchaser and indicated on the Data Sheet, Page 1.

All tanks and appurtenances shall comply with the Data Sheet and all attachments.

• Field-erected tanks shall be furnished completely erected, tested, and ready for service connections, unless specified otherwise. Shop-fabricated tanks shall be furnished tested and ready for installation.

• The appendices of this Standard provide a number of design options requiring decisions by the Purchaser, standard requirements, recommendations, and information that supplements the basic standard. Except for Appendix L, an appendix becomes a requirement only when the Purchaser specifies an option covered by that appendix or specifies the entire appendix. See Table 1-1 for the status of each appendix.

Appendix A provides alternative simplified design requirements for tanks where the stressed components, such as shell plates and reinforcing plates, are limited to a maximum nominal thickness of 12.5 mm (1/2 in.), including any corrosion allowance, and whose design metal temperature exceeds the minimums stated in the appendix.

Appendix AL provides requirements for aluminum tanks.

Appendix B provides recommendations for the design and construction of foundations for flat-bottom oil storage tanks.

Appendix C provides minimum requirements for pontoon-type and double-deck-type external floating roofs.

Appendix D provides requirements for submission of technical inquiries regarding this Standard.

• Appendix E provides minimum requirements for tanks subject to seismic loading. An alternative or supplemental design may be mutually agreed upon by the Manufacturer and the Purchaser.

Appendix F provides requirements for the design of tanks subject to a small internal pressure.

Appendix G provides requirements for aluminum dome roofs.

Appendix H provides minimum requirements that apply to an internal floating roof in a tank with a fixed roof at the top of the tank shell.

Appendix I provides acceptable construction details that may be specified by the Purchaser for design and construction of tank and foundation systems that provide leak detection and subgrade protection in the event of tank bottom leakage, and provides for tanks supported by grillage.

Appendix J provides requirements covering the complete shop assembly of tanks that do not exceed 6 m (20 ft) in diameter.

Appendix K provides a sample application of the variable-design-point method to determine shell-plate thicknesses.

Appendix L provides the Data Sheet and the Data Sheet instructions for listing required information to be used by the Purchaser and the Manufacturer. The use of the Data Sheet is mandatory, unless waived by the Purchaser.

Appendix M provides requirements for tanks with a maximum design temperature exceeding 93°C (200°F) but not exceeding 260°C (500°F).

Appendix N provides requirements for the use of new or unused plate and pipe materials that are not completely identified as complying with any listed specification for use in accordance with this Standard.

Appendix O provides recommendations for the design and construction of under-bottom connections for storage tanks.

Appendix P provides requirements for design of shell openings that conform to Tables 5-6a and 5-6b that are subject to external piping loads. An alternative or supplemental design may be agreed upon by the Purchaser or Manufacturer.

Appendix R provides a description of the load combinations used for the design equations appearing in this Standard.

Appendix S provides requirements for stainless steel tanks.

Appendix SC provides requirements for mixed material tanks using stainless steel (including austenitic and duplex) and carbon steel in the same tank for shell rings, bottom plates, roof structure, and other parts of a tank requiring high corrosion resistance.

Appendix T summarizes the requirements for inspection by method of examination and the reference sections within the Standard. The acceptance standards, inspector qualifications, and procedure requirements are also provided. This appendix is not intended to be used alone to determine the inspection requirements within this Standard. The specific requirements listed within each applicable section shall be followed in all cases.

Appendix U provides requirements covering the substitution of ultrasonic examination in lieu of radiographic examination.

Appendix V provides additional requirements for tanks that are designed to operate under external pressure (vacuum) conditions. 

Appendix W provides recommendations covering commercial and documentation issues. Alternative or supplemental requirements may be mutually agreed upon by the Manufacturer and the Purchaser.

Appendix X provides requirements for duplex stainless steel tanks.