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API MPMS 19.2 Document Information:
Title
Manual of Petroleum Measurement Standards Chapter 19 - Evaporative Loss Measurement Section 2 - Evaporative Loss from Floating-Roof Tanks
American Petroleum Institute
Publication Date:
Sep 1, 2003
Scope:
This publication contains methods for estimating the total evaporative
losses or the equivalent
atmospheric hydrocarbon emissions from external floating-roof tanks
(EFRTs) and freely vented
internal floating-roof tanks (IFRTs), as well as for tanks with
external-type floating roofs that
also have a freely vented fixed roof. This type of tank is referred to
as a covered floating-roof
tank (CFRT) in this document.
The equations that appeared separately in API Publ 2517 [1] and API
Publ 2519 [2] are combined in
this document. The standing storage loss factors have been revised to
reflect the results of the
most recent testing.
This publication was developed by the API Environmental Technical
Advisory Group. The equations and
factors presented are based on recent laboratory, test-tank, and
field-tank data and supercede
previous publications. The equations are intended to provide loss
estimates for general equipment
types, since it is not within the scope of this publication to address
proprietary equipment
designs.
Typical currently available types of floating roofs, rim-seal systems,
and deck fittings are
described for information only. This publication is not intended to be
used as a guide for
equipment design, selection, or operation.
The equations are intended to be used to estimate annual losses from
floating-roof tanks that
contain multicomponent hydrocarbon mixtures (such as petroleum stock
liquid like crude oils and
gasolines) or single-component hydrocarbon stocks (such as
petrochemicals). The equations are
applicable to the various types of tank construction, floating-roof
construction, rim-seal systems,
and deck fittings, as described in Section 8, as well as for various
stock liquid, stock vapor
pressures, tank sizes, and wind speeds (EFRTs). The equations are
applicable to properly maintained
equipment under normal working conditions.
The equations were developed for liquids that are not boiling, stocks
with a true vapor pressure
ranging from approximately 0.1 to less than 14.7 pounds per square in.
absolute (but not greater
than the atmospheric pressure at the tank location), average wind
speeds ranging from 0 miles per
hour (mph) - 15 mph (EFRTs), and tank diameters greater than 20 ft.
The estimation techniques
become more approximate when used to estimate losses for time periods
shorter than one year. 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.
b. To estimate losses from tanks in which the materials used in the
rim seal, deck fittings, or
deck seams have either deteriorated or been significantly permeated by
the stored stock.
c. To estimate losses from storage tanks that do not have a floating
roof of any kind.
d. To estimate losses from closed internal or covered floating-roof
tanks (that is, tanks vented
only through a pressure-vacuum relief vent, blanketed with an inert
gas, vented to a vapor
processing unit, or otherwise restricted from being freely vented).
The equations for estimating evaporative stock loss or the equivalent
total atmospheric emissions
from volatile stocks stored in floating-roof tanks are given in
Section 4. The factors for the
standing storage loss equation are discussed in Section 5 and for the
withdrawal loss equation in
Section 6. Sample problems illustrating the use of the equations are
provided in Section 7.
These loss-estimating procedures are applicable only to EFRTs (as
described in Appendix C of API
Std 650 Welded Steel Tanks for Oil Storage) [3], IFRTs of freely
vented design (as described in
Appendix H of API Std 650) [3], and CFRTs (as described in Appendix G
of API Std 650) [3] of freely
vented design (as described in Appendix H of API Std 650) [3].
Descriptions of the types of
construction covered by this publication are given in Section 8.
The bases and development of the loss-estimation procedures presented
in Sections 4 through 7 are
described in Section 9.
The estimation procedures were developed to provide estimates of
typical losses from floating-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
floating-roof tanks will be more accurate
than a loss estimate for an individual tank. It is difficult to
determine precise values of the
loss-related parameters for any individual tank.
Equipment should not be selected for use based solely on
evaporative-loss considerations. Many
other factors not addressed in this publication, such as tank
operation, maintenance, and safety,
are important in designing and selecting tank equipment for a given
application.
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