Repainted with other than heat-resistant paint.
Therefore, before you assume the refractory
requires re-working. check the following:
Condition of the tadpole gasket.
The condition of the insulating cement
protecting the tadpole gasket.
Horizontal baffle tile for large cracks, breaks,
chipped corners, and so forth.
Cracks in the castable refractory at the ends of
the baffle tile.
Tightness of door bolts.
Air line to the sight tube to ensure it is clear and
all connections are tight. If necessary, blow it
clear with an air hose.
It is normal for refractories exposed to hot gases to
develop thin "hairline" cracks. This by no means
indicates improper design or workmanship. Since
refractory materials expand and contract to some
degree with changes in temperature, they should be
expected to show minor cracks because of contraction
when examined at low temperature. Cracks up to
approximately one-eighth of an inch across may be
expected to close at high temperature. If there are any
cracks that are relatively large (1/8-inch to 1/4-inch
width), clean and fill them with high-temperature
bonding mortar. Any gap that shows between the
castable refractory and the baffle tile should be
filled-in in a similar fashion.
After opening the rear door, clean off the flange
surface of the door with a scraper or wire brush. Clean
the surface of the refractory carefully with a fiber brush
to avoid damaging the surface. Clean the mating
surfaces of the baffle tile and the boiler shell. Remove
all dried-out sealing material. Wash-coat the lower
half of the rear door refractory before closing it. The
upper half of the door contains a lightweight insulating
material similar to that used in the inner door. A thin
washcoat mixture applied gently with a brush is
helpful in maintaining a hard surface.
The front inner door is lined with a lightweight
castable insulation material. Thin "hairline" cracks
may develop after a period of time; however, these
cracks generally tend to close because of expansion
when the boiler is fired. Here, again, a thin washcoat
mixture is helpful in maintaining a hard surface. Minor
repairs can be accomplished by enlarging or cutting
out affected areas, making certain they are clean, and
then patching as required.
Should the entire installation require replacement,
remove existing material and clean to the bare metal.
Inspect the retaining pins and replace if necessary.
Reinforcing wire suitably attached may also be used.
The recommended insulation is known as Vee Block
Mix and is available in 50-pound bags. Mix the
material with water to a troweling consistency. Mixing
should be completely uniform with no portion either
wetter or drier than another. Trowel this mixture into
any areas that are being patched. If replacing complete
insulation, begin at the bottom of the door and apply
the mixture to a thickness equal to the protecting
shroud. With a trowel, apply the mixture horizontally
back and forth across the door in layers until the
required thickness is reached. Allow the mixture to
air-dry as long as possible. If immediate use of the
boiler is required, fire as slowly as possible to avoid
rapid drying of the material.
Whenever the front or rear door is opened for
inspection, the head gasket should be checked for
hardening and brittleness. Doubtful gaskets should be
replaced. Coat the gasket with an oil and graphite
mixture before closing the door. Make certain all
gaskets retaining rivets are in place. The flange of the
door should be clean and free of any hardened cement,
scale, and so forth. Check the condition of the rope
gasket used as a baffle seal. Replace if necessary. If the
rope is in good condition, liberally coat it with an
insulating pulp before closing. Make sure the rope is
If it is necessary to replace the rope, wire brush the
tube sheet area to remove all of the old sealing
material. Place a new piece of 1 1/2-inch-diameter rope
gasket on the lip of the baffle tile. Hold it in place with
furnace cement or an adhesive.
Earlier models have several steel bar
segments tack-welded across the tube
sheet to serve as a gasket retainer for
5/8-inch-diameter rope. It is suggested
that these bars are removed and 1
1/2-inch-diameter rope be used.
Generously apply a seal, consisting of a pulp
mixture of insulating cement and water, around the
entire rear door circumference. Place the pulp around
the inside diameter of the head gasket, as shown in
figure 2-16. Also coat the tube sheet area adjacent to
the baffle tile. When the door is closed, the pulp
compresses to protect the tadpole gasket and to form a