CHAPTER2
J.
PREPARATION
FOR
EXTENDED
LAY-UP
Many boilers
used
for heating
or
seasonal loads
or
for
stand-by
service
may
have
extended
periods
of
non-use. Special attention must be
given
to these boilers so that neither waterside
nor fireside surfaces are allowed
to
deteriorate
from corrosion.
Too many conditions exist
to
lay
down
definite
rules. There are two methods
of
storage:
wet
or
dry.
Your
Cleaver-Brooks local representative
can recommend the better method depending
upon circumstances
in
the particular installation.
Whichever method is used, common sense dic-
tates a periodic recheck
of
fli'eside and waterside
conditions during lay-up to allow variations from
the above methods for special area
or
job-site
conditions.
Swing open the boiler head at the
stack
end
of
the
unit
to
prevent the flow·
of
warm, moist air
through the boiler
tubes.
Although pollution control regulations may
con-
tinue to limit ihe permissible sulphur content
of
fuel oils, care must be taken to avoid corrosion
problems that sulphur can cause, especially
in
a
boiler that is seasonally shutdown.. Dormant
periods, and even frequent shutdowns, expose
the fireside surfaces
to
condensation below the
dew point during cooling. This moisture and any
sulphur residue
can
form an acid solution
..
Under
certain conditions, and especially in
areas
with
high humidity, the corrosive effect
of
the acid
will be serious enough
to eat through
or
severely
damage boiler tubes
or
other metal heating
sur-
faces during the time that a boiler is out
of
service.
This condition does not generally occur during
normal
fli'ing operation since the high tempera-
ture
of
operation vaporizes any condensation.
However, proper boiler operation must
be main-
THE
PRESSURE VESSEL
tained, especially with a hot water boiler, to
prevent the flue gases from falling below the dew
point.
At
the
start
of
lay-up, thoroughly clean the
fireside by removing any soot
or
other products
of
combustion from the tubes, tube sheets and
other
fireside surfaces. Brushing will generally
suffice.
Sweep
away
or
vacuum any accumula-
tion.
The
fireside surfaces may be flushed with
water. However, all moisture must be eliminated
after flushing and the surface dried by blowing
air
or
applying
some
form
of
heat. It is good
practice to protect the cleaned surfaces by
coat-
ing
them
with
an anti-corrosive material to
prevent rust.
To
prevent condensation from forming in the
control cabinet, keep the control circuit
ener-
gized.
For
extended lay-up periods, especially
where high humidity
or
large swings in ambient
temperature
occur,
the
control
should
be
removed and stored in a dry atmosphere.
Dry
storage is generally employed when the
boiler
will
be
out
of
service for some time
or
where freezing temperatures may exist. In this
method, the boiler must be thoroughly dried
be-
cause any moisture would cause corrosion. Both
fireside
·and
waterside surfaces must be cleaned
of
all scale, deposits, soot, etc. Steps must be
taken to eliminate moisture by placing moisture-
absorbing materials such
as
quick lime (at 2
pounds for 3 cubic feet
of
volume)
or
silica gel
(at
5 pounds for
30cubic
feet
of
volume)
on
trays
inside the vessel. Fireside surfaces may be coated
with an anti-corrosive material
or
grease
or
tar
paint. Refractories should be brushed clean and
wash
coaJ,eci.
All openings to the pressure vessel,
such
as
manhole and handholes, should be shut
tightly. Feed water and steam valves should
be
closed. Damper and vents should be closed to
prevent air from reaching fireside surfaces.
Peri-
odic inspection should be made and absorption
materials renewed.
Wet storage generally
is used for a boiler held in
stand-by condition
or
in cases where dry storage
is not practical.
The
possibility
of
freezing
temperatures must be considered. Care must
again be taken to protect metal surfaces. Vari-
750-150
To Next Page
Loading...
