[Illustration: Fig. 68.]
Fig. 68 represents a patch called a “spectacle piece.” This is used
to repair a crack situated between the tube ends. These are usually
caused (if the metal is not of bad quality) by allowing incrustation to
collect on the plate inside the boiler, or by opening the furnace and
smoke doors, thus allowing a current of cold air to contract the metal
of the plates round the heated and expanded tubes.
The “spectacle piece” is bored out to encircle the tubes adjacent
to the crack, or in other words, to be a duplicate of a portion of
the tube plate cracked. These plates are then pinned on to the tube
covering the crack.
Steam generators, as they are exposed to more or less of trying service
in steam production, develop almost an unending number and variety of
defects.
When a boiler is new and first set up it is supposed to be clean,
inside and out, but even one day’s service changes its condition;
sediment has collected within and soot and ashes without.
Unlike animals and plants they have no recuperative powers of their
own—whenever they become weakened at any point the natural course of
the defect is to become continually worse.
In nothing can an engineer better show his true fitness than in the
treatment of the beginnings of defects as they show themselves by
well-known signs of distress, such as leaks of water about the tube
ends, and in the boiler below the water line, or escaping steam above
it. In more serious cases, the professional services of a skillful and
honest boiler maker is the best for the occasion.
In a recent report given in by the Inspectors the following list of
defects in boilers coming under their observation was reported. The
items indicate the nature of the natural decay to which steam boilers
in active use are exposed. The added column under the heading of
“dangerous” carries its own lesson, urging the importance of vigilance
and skill on the part of the engineer in charge.
Nature of Defects. Whole Number. Dangerous.
Cases of deposit of sediment 419 36
Cases of incrustation and scale 596 44
Cases of internal grooving 25 16
Cases of internal corrosion 139 21
Cases of external corrosion 347 114
Broken and loose braces and stays 83 50
Settings defective 129 14
Furnaces out of shape 171 14
Fractured plates 181 84
Burned plates 93 31
Blistered plates 232 22
Cases of defective riveting 306 34
Defective heads 36 20
Serious leakage around tube ends 549 57
Serious leakage at seams 214 53
Defective water gauges 128 14
Defective blow-offs 45 9
Cases of deficiency of water 9 4
Safety-valves overloaded 22 7
Safety-valves defective in construction 41 16
Pressure-gauges defective 211 29
Boiler without pressure-gauges 3 0
This list covers nearly, if not all, _the points of danger_ against
which the vigilance of both engineer and fireman should be continually
on guard; and is worth constant study until thoroughly memorized.