Model ATF921 Specification

Provide and install _____ Anchorage Tank Model AT___F921 UL® listed aboveground secondary containment tank(s). Tank(s) shall be approximately _____in diameter, _____ long, having a normal volume of _____ gallons. Tanks shall bear the Steel Tank Institute F921® identification label.


Provide shop drawings for the aboveground storage tank that show principal dimensions, materials, and location of fittings.

General Characteristics

The entire tank system, including the skid and secondary containment, shall be listed by Underwriters Laboratories under UL® 142 Standard for Safety as a complete, indivisible unit. The skid mounted tank assembly shall bear the UL® listing mark.

Type I Tank

Construction of the outer tank shall be separate but in intimate contact with the inner tank and shall encompass 300 degrees of the circumference. The material thickness of the inner and outer tank shells and the tank heads shall be that required by the Anchorage Tank's UL® 142 listing. Head bracing shall be as required by the Standard.


The skid rails shall be constructed of structural steel beam and shall be listed as an integral part of the tank. Skid supports shall be constructed of plate steel, equal in thickness to the inner tank, with a 90 degree bent edge 1" wide on each side for structural support. Supports shall be placed directly under the inner tank heads and thereafter, evenly spaced along the tank, provided however, that such spacing shall not exceed 69". The skid supports shall be attached to a 12" wide saddle pad attached to the outer tank shell which is of sufficient length to encompass its bottom 120 degrees. A capped length of Schedule 80 pipe shall be attached to each end of the skid to function as a tow bar when the tank is empty. The full 360 degrees of the tow bar shall be encircled by the beam members.

Weld Joints

All joints on the inner and outer shell and the tank heads shall be that required by Anchorage Tank's UL® 142 listing.

In addition, all nonstructural external seams shall be seal welded before painting. All weld spatter shall be removed and all sharp edges shall be rounded and smoothed by grinding.

Flat unflanged heads are not permitted on either the inner or outer tank.

Tank Attachments and Penetrations

Piping penetrations shall be made through the top of the tank only.

The secondary containment shall allow for the full recovery of a release into the annular space.

An additional fitting shall be incorporated into the tank (typically located on the top of the opposite end of the tank from the monitor port) to allow for flushing of any product which may accumulate as the result of a release or accidental fill of the annular space.

Each tank shall be equipped with lifting lugs adequate for the safe handling of the tank during installation.

Each lifting lug must be designed to support the total weight of the dual wall tank.

A minimum of two lifting lugs shall be provided on tanks having a rated capacity of more than 1100 gallons.


Inner tank shall be equipped with normal and emergency venting in accordance with UL® 142.

Outer tank shall be equipped with emergency venting in accordance with UL® 142. The emergency relief venting for the annular space shall be calculated based upon the outer shell dimensions.

Long bolt manways, as defined within UL® 142, Section 10.5, shall not be used to provide emergency relief venting. Emergency vents shall be elevated 24" above the tank top center line. The interstitial space shall be vented using a pressure vacuum vent rated at 8 oz. per square inch.

Monitoring Annular Space

Monitoring of the annular space may be accomplished by one or more of the following methods:

  • Visual inspection (monitoring pipe with dipstick).
  • Electronic Monitoring (constant liquid or vapor detection).
  • Mechanical (float devices).

Inspection and Testing

Each tank, before painting, shall be tested per UL® 142 by Anchorage Tank to determine that the tank does not leak. If leaks are noted during the test, they shall be repaired by rewelded and the tank retested.


If the tank is to be coated, all exterior surfaces shall be cleaned and prepared by sandblasting in accordance with Steel Structures Painting SSPC-3 and thereafter, coated per the coating manufacturer's recommendations. It shall not be necessary to blast and paint the interstice.

Thread protectors or plugs shall be installed in each opening during storage and shipment to provide normal venting of the tank in storage.

Installation and field testing shall be per Steel Tank Institute F921® Standard.

Specification in Adobe PDF format.