scope:

This standard contains methodologies for estimating the total evaporative losses of hydrocarbons from fixedroof tanks. The methodologies provide loss estimates for general equipment types based on laboratory, testtank and field-tank data.

Types of fixed-roof tanks and roof fittings described are for information only.

The equations estimate average annual losses from uninsulated fixed-roof tanks for various liquid stocks, stock vapor pressures, tank sizes, meteorological conditions, and operating conditions.

The following special cases are addressed:

a) Horizontal tanks.

b) Higher volatility stocks (true vapor pressure greater than 0.1 psia).

c) Vent settings higher than 0.03 psia (0.5 oz/in²).

The estimation may be improved by using detailed field information, including climatic data and operational data for the appropriate time period.

The equations are not intended to be used in the following applications:

a) To estimate losses from unstable or boiling stocks or from petroleum liquids or petrochemicals for which the vapor pressure is not known or cannot readily be predicted (to calculate emissions from tanks that contain material at or above their boiling point or the point at which material starts to flash, the API model E&P Tank (API Publication 4697) can be used).

b) To estimate losses from fixed-roof tanks which have an internal floating roof. API MPMS Ch. 19.2^[4] and API TR 2569^[13] address these.

c) To estimate losses from fixed-roof tanks which have either roof or shell insulation.

d) To estimate losses from cleaning fixed-roof tanks. API TR 2568^[12] addresses this.

The estimation procedures were developed to provide estimates of typical losses from fixed-roof tanks that are properly maintained and in normal working condition. Losses from poorly maintained tanks may be greater. Because the loss equations are based on equipment conditions that represent a large population of tanks, a loss estimate for a group of fixed-roof tanks may be more representative than a loss estimate for an individual tank.

Evaporative loss considerations are not the only criteria for equipment selection. Many other factors not addressed in this standard, such as tank operation, maintenance, and safety, are important in designing and selecting tank equipment for a given application.