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API PUBL 2558 Document Information:
Title
Wind Tunnel Testing of External Floating-Roof Storage Tanks
American Petroleum Institute
Publication Date:
Jan 1, 1993
Scope:
The American Petroleum Institute (API) contracted with Cermak Peterka
Petersen, Inc. (CPP) to
conduct a wind tunnel study to determine the local wind velocities,
wind directions, and roof
pressures on External Floating Roof Tanks (EFRT). The results of this
study are to be used to
improve evaporative loss calculations for roof fittings on EFRT.
The third edition of API Publication 2517 (1989) is the first to
include roof fittings as a
potential source for evaporative loss. Previous publications have
limited the scope to include rim
seal and stock clingage losses, assuming roof fitting losses to be
negligible in comparison. The
loss factors used in the evaporative equations were derived from
experimental data which correlated
stock evaporation to the wind speed over the roof fitting.
The current procedure, as described in Section 2.2 of API 2517,
specifies that an average wind
speed at the tank site or from the nearest local weather station
should be used as the wind speed
over the roof fitting in the evaporative loss equations. This average
approach wind speed may
differ Substantially from the actual wind speed over the fittings,
from which the loss factors were
derived. For lower roof levels, in particular, the inaccuracy in wind
velocity may cause
overestimates of the evaporative loss potential for the roof fittings.
The primary objective of this study is to develop a relationship
between the airport wind speed and
the wind speed at roof fittings. In addition to wind speed, the
relative wind direction of air flow
over the EFRT roof top will be analyzed as an aid to evaluating
evaporation losses for fittings
which exhibit some level of directional sensitivity. For documentation
purposes and for use in
future evaluations of evaporative loss, roof top pressures were also
measured across the tank.
The following sections provide background into the current evaporative
loss methodology and air
flow characteristics, a description of the experimental program
carried out during the study,
results of the study, a revised method for calculating evaporation
loss from roof fittings, and
conclusion and recommendations.
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