scope:

This Code provides minimum requirements for design and construction of reinforced concrete and prestressed concrete structures for the storage and containment of refrigerated liquefied gases (RLGs) with service temperatures between +40 and -325°F.

Container design shall include the design of the container wall, its foundation (footing and floor slab), the concrete portions of its roof, and the bund wall, if applicable.

Design and detailing requirements not specifically covered by this Code shall comply with ACI 350 and national design standards as specified in the project documents. In case of conflict between the requirements of ACI 350 and national standards, the more stringent requirements shall apply.

Typically, reinforced concrete and prestresssed concrete structures for the containment of RLGs are classified into two main categories:

(a) Secondary containment, which represents the most widespread use of such structures

(b) Primary containment

In this Code, the term "concrete" is used to denote both concrete reinforced with nonprestressed reinforcement and prestressed concrete.

Appendix D has been added in this version of the Code that includes design and detailing requirements for membrane tanks. A membrane tank has a non-self-supporting thin layer (membrane) that is supported through insulation by an outer concrete tank that structurally is the primary container and secondary container.

This Code does not address the materials, design, or construction of steel primary or secondary tanks. Such information is further described in API 620.

This Code has been developed with the lowest operating temperature of -325°F. Lower product temperatures could also be used, however, provided appropriate additional engineering analysis and justification is performed for each proposed application. Single-containment, double-containment, and full-containment concepts are covered by this Code.

A concrete bund wall is an open-top cylindrical wall serving as the outer boundary of an impounding area surrounding a single-containment RLG storage tank.

In a double-containment tank system, the primary container is normally a single-containment RLG storage tank with a vapor-tight shell and roof designed to contain both refrigerated liquid and the associated vapors under normal operating conditions. In this system, the secondary container is often an open-top concrete wall that serves two basic functions:

1. Provides protection to the primary container from external loads under normal operating conditions.

2. Contains the leakage from the primary container (but not the vapor generated from such leakage) under accidental-spill conditions.

In a full-containment tank system, the primary container is designed to contain the refrigerated liquid under normal operating conditions. In this system, the secondary container is a vapor-tight wall with a vapor-tight roof that spans over the inner tank. The roof may be constructed of metal, concrete, or a composite of the two materials.

Under normal operating conditions, the secondary container provides protection to the primary container from external loads. Under accidental-spill conditions, the secondary container also contains the leakage from the primary container and contains or controls the vapor generated from such leakage.

New design and detailing requirements have been added for the thermal corner protection (TCP) embedment plate and secondary containment wall in the vicinity of the TCP embedment plate.

ACI 350 is intended to be used for those aspects of concrete design not specifically covered by this Code such as reinforcement development length, calculation of prestress losses, and strength design procedures. The user should be familiar with ACI 350 provisions and implement appropriate provisions as applicable. It is noted that the properties and operating temperature range of the liquid products stored in RLG tank structures covered by this Code are fundamentally different from that of liquids covered by the provisions of ACI 350. To consider this, specific references to ACI 350 together with appropriate modifications are provided in this Code.

Although like concrete liquid-containing structures in ACI 350, the design and construction of concrete RLG containers are more complex due to cold storage temperatures and safety associated with preventing release of gas or liquid into the environment. For an overview of the design and construction topics covered by the Code, refer to Bruggeling (1978) and Roetzer (2020).