Cracks in the crown-sheet or side of a fire-box boiler, or top head
of the upright boiler can be temporarily repaired by a row of holes
drilled and tapped touching one another, with 3/8 or 1/2 inch copper
plugs or bolts, screwed into the plates and afterwards all hammered
together.
For a permanent job, cut out the defect and rivet on a patch. This had
better be put on the inside, so as to avoid a “pocket” for holding the
dirt. In putting on all patches, the defective part must be entirely
removed to the solid iron, especially when exposed to the fire.
NOTE.—When fire comes to two surfaces of any considerable extent, the
plate next to the fire becomes red-hot and weakens, hence the inside
plate, in repairs, must be removed.
The application of steel patches to iron boilers is injudicious. Steel
and iron differ structurally and in every other particular, and their
expansion and contraction under the influence of changing temperatures,
is such that trouble is sure to result from their combination.