The Pressure Vessel
2-10
750-96 (revised 2010)
Model CB Packaged Boiler Manual
2.7 — Washing Out
2.7.1 — Hot Water Boiler
In theory, a hot water system and boiler that has been initially cleaned, filled with raw water (and that water
treated), and with no makeup water added, will require no further cleaning or treatment. However, since the sys-
tem (new or old) may allow entrance of air and unnoticed or undetected leakage of water, introductions of raw
water makeup or air may lead to pitting, corrosion, and formation 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 three months after ini-
tially placing the boiler into operation and periodically thereafter as indicated by conditions observed during
inspections.
2.7.2 — Steam Boiler
No later than three 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 tempera-
ture, hand hole covers removed, and waterside surfaces inspected for corrosion, pitting, or formation of deposits.
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 consul-
tant or feedwater treatment company, and in extreme cases, it may be necessary to resort to acid cleaning. Pro-
fessional advice is recommended if acid cleaning is required.
These inspections will indicate the effectiveness of the feedwater treatment. The effectiveness of treatment, the
water conditions, and the amount of fresh water makeup required are all factors to be considered in establishing
frequency of future pressure vessel washout periods. The feedwater consultant or water treatment company ser-
vice should include periodic pressure vessel inspection and water re-analysis.
2.8 — Blowdown: Steam Boiler
Boiler water blowdown is the removal of some of the concentrated water from the pressure vessel and its replace-
ment 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
that are designed to remove unwanted substances which contribute to scale and deposit formations. However,
none of these are in themselves capable of removing all substances and regardless of their high efficiency, a small
amount of encrusting solids will be present in the boiler water.
Solids become less soluble in the high temperature of the boiler water and tend to crystallize and concentrate 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
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