of the burner front, and they are called parallel
cracks. Parallel cracks usually appear at or slightly
behind the leading edge of the bladed cone. They
are not dangerous until they actually loosen pieces
of the burner front. Improper installation and
boiler operation are usually the cause of parallel
A slanting crack in the narrow section between
the burners sometimes joins a radial crack. When
this occurs, pieces of plastic tend to break off.
This type of damage can usually be repaired by
a plastic patch.
If during your inspection you find that a
castable burner front is breaking up after very
little service, it is likely that too much water was
used in mixing the material during installation.
Sometimes the material is already partially set
before installation; a common cause of this
trouble is that the castable material, while in
storage, reacted with moisture in the air and
started to set. When castable material sets before
it is used, it can never reach full strength.
Castable material is also subject to spalling
after several hours of service. The peeling
material, usually in 1/8-inch strips, should not be
removed unless it is in the burner cone and is
interfering with combustion.
If a castable front is chalky or crumbly, find
out how deep the condition goes. If no more than
the surface can be rubbed off, the burner front
is not seriously damaged. Do not remove the
crumbly material. The condition is serious only
if the burner cone is affected or if the casing shows
signs of overheating.
Burner tile should be inspected for loose
segments and broken pieces that might cause
improper cone angles. The broken or damaged
segments can be repaired by patching with plastic
fireclay refractory. In some cases a new segment
of tile can be installed.
When you inspect boiler refractories, it
is a good idea to keep in mind the possibility
that damage may occur because of operational
problems. Although boilers must occasionally be
operated under very severe and damaging condi-
tions, a lot of damage to refractories (and, in fact,
to other boiler parts as well) is caused by poor
operating procedures that are really not necessary
under the circumstances. It may be helpful to
show operating personnel any refractory damage
that appears to be directly related to poor
operation of the boiler.
When inspecting the exterior of boiler tubes,
look for signs of warping, bulging, sagging,
cracking, pitting, scaling, acid corrosion, and
other damage. All tube sheets should be inspected
for signs of leakage, especially the superheater
Inspection of boilers sometimes shows an
unexpected condition in which adjacent boiler
tubes are warped in such a way that they touch
each other. When this condition exists, the tubes
are said to be married. Tube marriages can result
either from overheating of the tubes or from
stresses developed in the tubes during installation.
For the latter reason, newly erected boilers and
boilers that have been retubed should always be
inspected for tube alignment after the initial
period of steaming.
When inspection reveals one or more tube
marriages, the decision as to whether or not the
married tubes should be renewed should be
based on the following considerations:
1. If the tube marriage occurs in screen tubes
1 1/2 inches or larger, or if the furnace side wall
or rear wall tubes are bowed, tube replacement
is usually required.
2. If 1-inch or 1 1/4-inch tubes in the main
bank of generating tubes are married, replacement
is usually not required if the tube joints are tight
under hydrostatic test.
3. Inspect the external surfaces of the tubes.
If they show blistering or other signs of over-
heating, the tubes should be renewed.
4. Inspect the watersides. Where tube mar-
riages exists, a poor waterside condition may
indicate hard scale or oil within the affected tubes.
If hard scale or oil does exist, the married tubes
should be replaced, and all appropriate steps
should be taken to remove the scale or oil from
the rest of the boiler. If the condition of the
tubes is uncertain, or if a large number of tube
marriages have occurred, remove one or more
sample tubes, split them, and examine them
5. Tube marriages may cause gas laning,
and gas laning, in turn, may cause local over-
heating of the inner casing, the bottom part
of the economizer, and other parts. Inspect
the boiler carefully for signs of local over-
heating that might have been caused by gas
laning resulting from the tube marriages. If
the local overheating from this cause is found,
renew the married tubes.