ICI - Innovative Creations, Inc. AX - Manual (Page 15)

MAINTENANCE
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5.3 SCHEDULED
All boilers must be periodically stopped for careful inspection and maintenance: the time interval between
stops is established by experience, by the operating conditions, by the quality of the feed water and by the
type of fuel used.
Before entering the boiler shell for inspection or for cleaning, check carefully that there is no possibility of
entry of water or steam via the pipework to which the boiler is connected. Every valve must be locked and if
necessary isolated by removing a piece of pipework or by inserting a blind flange.
The parts under pressure must be carefully examined internally to identify any encrustation, corrosion and
other potential sources of danger linked to the feed water.
All deposits must be removed mechanically or chemically and the effective thickness of the structures
must be verified using suitable instruments to determine that they are equal to or greater than the
design values. All pustules or other types of corrosion must be scraped and cleaned with a steel wire brush
to white metal. Leaks between fire tubes and tube plates must be carefully examined: any welding must be
done in all cases observing legal obligations, without forgetting that a steam boiler is a pressure vessel with
danger of explosion and subject to control by competent authorities.
During inspection also verify all the accessories, with priority to safety valves, level probes and pressure
switches.
5.4 CONSERVATION DURING WHEN OUT OF SERVICE
Often during periods of disuse the worst cases of corrosion appear. The operations to be carried out to
guarantee correct conservation of the boiler depend essentially on the duration of the stop.
The boiler can be subjected to dry conservation if the period of disuse is long, or to a wet conservation for
short stops or if the boiler has a back-up function and must be ready to come on-line in a short time.
In both cases, the necessary operations tend to eliminate the causes of possible corrosion.
5.4.1 Dry conservation
The boiler must be drained and dried carefully, then placing in the boiler shell a hygroscopic substance (for
example lime or silica gel etc)
5.4.2 Wet conservation
The boiler must be filled completely, given that corrosion is a phenomenon that appears due to the
simultaneous presence of water and Oxygen. Therefore all traces of Oxygen must be removed from the
water, also avoiding the successive infiltration of air. There are substances that absorb Oxygen, such as
hydrazine and Sodium Sulphite, but after their use the water alkalinity must be checked.