Probably one-quarter, if not one-third, of all boiler-work is done
in the way of repairs, hence the advice of men who have had long
experience in the trade is the one safe thing to follow for the
avoidance of danger and greater losses, and for the best results the
united opinion of 1, the engineer, experienced in his own boiler and
2, the boiler-maker with his wider observation and 3, the owner of the
steam plant, all of whom are most interested.
Corrosion is a trouble from which few if any boilers escape. The
principal causes of external corrosion arise from undue exposure to
the weather, improper setting, or possibly damp brick work, leakage
consequent upon faulty construction, or negligence on the part of those
having them in charge.
Internal corrosion maybe divided into ordinary corroding, or rusting
and pitting. Ordinary corrosion is sometimes uniform through a large
portion of the boiler, but is often found in isolated patches which
have been difficult to account for. Pitting is still more capricious in
the location of its attack; it may be described as a series of holes
often running into each other in lines and patches, eaten into the
surface of the iron to a depth sometimes of one-quarter of an inch.
Pitting is the more dangerous form of corrosion, and the dangers are
increased when its existence is hidden beneath a coating of scale.
There is another form of decay in boilers known as grooving; it may
be described as surface cracking of iron, caused by its expansion and
contraction, under the influence of differing temperatures. It is
attributable generally to the too great rigidity of the parts of the
boiler affected, and it may be looked upon as resulting from faulty
construction.
[Illustration: Fig. 69.]
In plugging a leaky tube with a pine plug, make a small hole, of 3/16
of an inch diameter, or less, running through it from end to end. These
plugs should never have a taper of more than 1/8 of an inch to the
foot. It is well to have a few plugs always on hand. Fig. 69 exhibits
the best shape for the wooden plug.