The Locomotive - Lighthouse Survival Blog

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PUBLISHED BY THE HARTFORD STEAM BOILER INSPECTION AND INSURANCE COMPANY.
New Seuiks — Vol. XIV. HARTFORD, CONN., NOVEMIiEH, 1893. No. 11.
Cracked Plates.
There are certain classes of defcct.s iu boilers, that boiler owners know about, and
endeavor to avoid. Among these are the deposit of sediment and .scale, leakage
around tube-ends and along riveted joints, and overloaded safety-valves. These defects
rather force themselves on the attention of the owners; but there are many other kinds
of defects that are not so obvious, though they may be fully as dangerous. Among
these less patent defects are cracked plates.
Frequently cracks start from the edge of the plate, opposite a rivet-hole, in the
girth-joint that comes over the fire. Such cracks are often due to distress at the joint
arising from an improper arrangement of the feed-pipe; for if the comparatively cold
Fig. 1. — A Cracked Plate.
feed-water is discharged on or near the fire-sheet, it chills the shell in that vicinity, and
produces a powerful local contraction of the metal, which is quite sufficient to start the
joints, or, under some circumstances, to even crack the solid plate. But whatever the
cause of the cracks, they are likely to first appear at the edge of one of the fire-
sheets, and to extend gradually inward. Often they are stopped by running into the
rivet hole, and do not extend further. Frequently, however, they run past the rivethole,
or cross it and extend into the sheet on the further side of it. It then becomes
very important to check their further progress. This may often be done by drilling a
small hole through the sheet at the very extremity of the crack. This hole may after-
w'ards be filled with a rivet, or it may be tapped and filled with a screw plug.
Besides these fire-sheet cracks there are numerous other kinds, due to different
causes. For example, the strength of a plate may be injured by overheating, or
"burning," so as to develop a serious crack under the ordinary rimning conditions,
without any assignable reason except that it has become too weak to withstand the strain
that comes upon it in ordinary usage. Cracks are often discovered, too, along flanges