24 July 2003
including Change 1, Jan 2004 and Change 2, March 2005
PROCEDURES FOR LAY-UP OF BOILERS
Guidance. When a boiler is taken out of service, the boiler should be cooled
until the water is below the atmospheric boiling point, but not below 82.2 C (180F); the
boiler should be emptied and flushed out. An inspection should be made to determine
what repair work is necessary and what mechanical and chemical cleaning should be
done. A decision should then be made on whether to employ dry storage or wet
storage. Since freshly cleaned metal surfaces are much more vulnerable to corrosion
than surfaces that have operational oxides on them, prefer delay of chemical cleaning
until the boiler is ready to be returned to service.
. This procedure
is preferred for boilers out
of service for extended
periods of time or in locations where freezing temperatures may be expected during
D-2.1 The boiler should be thoroughly dried, since any moisture left on the metal
surface would cause corrosion to occur on long standby. After drying, precautions
should be taken to preclude entry of moisture in any form from steam lines, feed lines,
D-2.2 Moisture absorbing material, such as quicklime at the rate of 0.9 kg (2 lbs,) or
silica gel at the rate of 2.3 kg (5 lbs), for 0.85 cu. meters (30 cu. feet) of boiler volume, is
placed on trays inside the drums to absorb moisture from the air. The manholes should
then be closed and all connections on the boiler should be tightly blanked. The
effectiveness of materials for such purposes and need for their renewal may be
determined through regular internal boiler inspections.
D-2.3 Alternatively, air dried externally to the boiler may be circulated through it. The
distribution should be carefully checked to be sure the air flows over all areas.
D-2.4 It is usually desirable in the case of large utility boilers (particularly the once-
through type) to simply drain the boiler while feeding nitrogen to the boiler vents and
maintaining a 34.47 kPa (5-psig) nitrogen gage pressure during the storage period.
Wet Storage. A wet procedure may be used for a boiler to be placed in a
standby condition. Wet storage is particularly useful if the standby boiler may be
required for service at short notice or it is impractical to employ a dry storage procedure.
The method is not generally employed for reheaters or for boilers that may be subject to
freezing temperatures. Several procedures have been employed.
D-3.1 The empty boiler should be closed and filled to the top with water conditioned
chemically to minimize corrosion during standby. Water pressure greater than
atmospheric should be maintained within the boiler during the storage period. A head
tank may be connected to the highest vent of the boiler to maintain a pressure above