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.
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.
QUESTIONS
BY THE PROPRIETOR TO THE ENGINEER IN CHARGE, RELATING TO CONDITION OF THE BOILER,
How long since you were inside your boiler?
Were any of the braces slack?