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 properly positioned.

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.

NOTE

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