MIL-HDBK-1003/7
blowout of the steam to the outdoors. Temporary piping shall be designed in accordance
with the requirements of the Power Piping Code, ANSI/ASME B31.1. The temporary piping
and valves shall be sized to obtain a cleaning ratio of 1.0 or greater in all permanent
piping to be cleaned. The cleanout ratio is determined using the following equation.
R = (Qc/Qm)2
EQUATION:
x
[(Pv)c/(Pv)m]
x
(Pm/Pc]
(4)
where:
R
= Cleaning ratio
Qc
= Flow during cleaning, lb/h
Qm
= Maximum load flow, lb/h
(Pv)c = Pressure-specific volume product during cleaning at boiler
outlet, ft3/in2.
(Pv)m = Pressure-specific volume product at maximum load flow at
boiler outlet, ft3/in2
Pm
= Pressure at maximum load flow at boiler outlet, psia
Pc
= Pressure during cleaning at boiler outlet, psia
This design procedure is applicable to fossil fuel-fired power plants, And
is written specifically for drum (controlled circulation) type boilers but may be
adapted to once-through (combined circulation) type boilers by making appropriate
modifications to the procedure. The same basic concepts for cleaning piping systems
apply to all boiler types.
b) Blowout Sequence. Boiler and turbine manufacturers provide a
recommended blowout sequence for the main and reheat steam lines.
The most satisfactory method for cleaning installed piping is to utilize the
following cleaning cycle:
(1) Rapid heating (thermal shock helps remove adhered particles).
(2) High velocity steam blowout to atmosphere.
(3) Thermal cool down prior to next cycle.
The above cycle is repeated until the steam emerging from the blowdown
piping is observed to be clean.
5.15.1.3 Installation of Temporary Strainers. Temporary strainers shall be installed
in the piping system at the suction of the condensate and boiler feed pumps to
facilitate removal of debris within the piping systems resulting from the installation
procedures. The strainers shall be cleaned during the course of all flushing and
chemical cleaning operations. The temporary strainers shall be removed after completion
of the flushing and chemical cleaning procedures.
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