Cleaver-Brooks CBH 40 - Washing out

is heated to at least 180°F to drive off any
dissolved gases which might otherwise
corrode the metal.
The above procedure may be omitted in the case of
a unit previously used or known to be internally
clean, however, consideration must be given to the
possibility of contaminating materials entering the
boiler from the system.
On a steam system, the condensate should be
wasted until tests show the elimination of un-
desirable impurities. During the period that con-
densate is wasted, attention must be given to the
treatment of the raw water used as makeup so that
an accumulation of unwanted materials or
corrosion does not occur. Follow the advice of your
water treating company.
On a hot water system, chemical cleaning is
generally necessary and the entire system should
be drained after treatment. Consult water treat-
ment companies for recommendations, cleaning
compounds and application procedure.
G. WASHING OUT
A. STEAM BOlliER
No later than 3 months after initially placing the
boiler into operation and starting service, and
thereafter as conditions warrant, the pressure
vessel should be drained after being properly
cooled to near ambient temperature, handhole
covers removed and internal waterside surfaces in-
spected for corrosion, pitting, or formation of
deposits.
B. HOT WATER BOlliER
In theory, a hot water system and boiler that has
been initially cleaned, filled with raw water (and
that water treated) and with no make-up water ad-
ded will require no further cleaning or treatment.
However, since the system (new or old) may allow
entrance of air and unnoticed or undetected
leakage of water, introductions of raw water make-
up or air may lead to pitting, corrosion and for-
mation of sludge, sediment, scale, etc., on the
pressure vessel waterside.
If the operator is absolutely certain that the system
is
tight, then an annual waterside inspection may
be sufficient.
If there is any doubt then the pressure vessel
waterside should be inspected no later than 3
months after initially placing the boiler into
operation and periodically thereafter as indicated
by conditions observed during inspections.
flUSHING Of PRESSURE VESSEl INTERIOR
Upon completion of inspection, the pressure vessel
interior should be flushed out as required with a
high pressure hose. If deposits are not fully
removed by flushing this may require immediate
consultation with your water consultant or feed-
Chapter 2- The Pressure Vessel
water treatment company, and in extreme cases, it
may be necessary to resort to acid cleaning.
Professional advice is recommended if acid
cleaning is required.
These inspections will indicate the effectiveness of
the feed water treatment. The effectiveness of treat-
ment, the water conditions, and the amount of
fresh water make-up required are all factors to be
considered in establishing frequency of future
pressure vessel washout periods. The feedwater
consultant or water treatment company service
should include periodic pressure vessel inspection
and water re-analysis.
H. SlOWDOWN - STEAM BOILER
Boiler water blowdown is the removal of some of
the concentrated water from the pressure vessel
and its replacement with feedwater so that a
lowering of the concentration in the boiler water
occurs.
Solids are brought in by the feedwater even though
this water is treated prior to use through external
processes designed to remove the unwanted sub-
stances that contribute to scale and deposit for-
mations. However, none of these are in themselves
capable of removing all substances and regardless
of their high efficiency, a small amount of en-
crusting solids will be present in the boiler water.
Solids become less soluble in the high temperature
of the boiler water and tend to crystalize and con-
centrate on heating surfaces. Internal chemical
treatment is, therefore, required to prevent the
solids from forming harmful scale and sludge.
Scale has a low heat transfer value and acts as an
insulation barrier. This retards heat transfer,
which not only results in lower operating efficiency
and consequently higher fuel consumption, but
more importantly can cause overheating of boiler
metal. This can result in tube failures or other
pressure vessel metal damage causing boiler down
time and costly repairs.
Scale is caused primarily by calcium and
magnesium salts, silica and oil. Any calcium and
magnesium salts in the boiler water are generally
precipitated by the use of sodium phosphate along
with organic materials to maintain these precipi-
tates or "sludge" in a fluid form. The solids such
as sodium salts and suspended dirt do not readily
form scale, but as the boiler water boils off as
relatively pure steam, the remaining water is
thicker with the solids. If this concentration is per-
mitted to accumulate, foaming and priming will
occur and the sludge can cause harmful deposits
that bring about overheating of the metal.
The lowering or removal of this concentration
requires the use of boiler water blowdown.
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