Api 650 - H App

Annex H

(normative)

Internal Floating Roofs

H.1 Scope

H.1.1 This Annex provides minimum requirements that apply to a tank with an internal floating roof and a fixed

roof at the top of the tank shell, and to the tank appurtenances. This Annex is intended to limit only those factors

that affect the safety and durability of the installation and that are considered to be consistent 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 provided as a basic guide and shall not be considered to restrict the Purchaser option of

employing other commonly accepted or alternative designs, as long as all design loading 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). The requirements apply to the internal floating roof of a new tank and may be applied to an

existing fixed-roof tank. Section 5.10 of this standard is applicable, except as modified in this Annex.

H.1.2 The Purchaser is required to provide all applicable jurisdictional requirements that apply to internal floating roofs

(see 1.3).

H.1.3 See Annex W for bid requirements pertaining to internal floating roofs.

H.2 Types of Internal Floating Roofs

H.2.1 The internal floating roof type shall be selected by the Purchaser after consideration of both proposed and

future product service, operating conditions, maintenance requirements, regulatory compliance, service life

expectancy, ambient temperature, maximum design temperature, product vapor pressure, corrosion conditions and

other compatibility factors. Other operating conditions requiring consideration include (but are not limited to)

anticipated pumping rates, roof landing cycles, and the potential for turbulence resulting from upsets, such as vapor

slugs injected into the tank. Safety and risk factors associated with the roof types shall also be evaluated.26 The type

of roof, which shall be designated by the Purchaser on the Data Sheet, Line 30, shall be one of the types described in

H.2.2.

H.2.2 The following types of internal floating roofs are described in this Annex.

a) Metallic pan internal floating roofs 27,28,29 have a peripheral rim above the liquid for buoyancy. These roofs are in

full contact with the liquid surface and are typically constructed of steel.

b) Metallic open-top bulk-headed internal floating roofs 26,27 have peripheral open-top bulk-headed compartments

for buoyancy. Distributed open-top bulk-headed compartments shall be used as required. These roofs are in full

contact with the liquid surface and are typically constructed of steel.

26 Internal floating

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