The Locomotive - Lighthouse Survival Blog

PUBLISHED BY THE HARTFORD STEAM BOILER INSPECTION AND INSURANCE COMPANY,
Vol. XXII. HARTFORD, CONN., MAY, 1901. No. 5.
A Common Defect in Bracing".
We have discussed the matter of bracing boilers very fully in previous issues of
The Locomotive; and the subject is so comparatively simple that it might be sup-
posed that we had practically exhausted it. But there is always something more to be
said about every topic under the sun,— even about bracing.
These remarks are called forth by the fact that boiler makers have a habit of not
making their braces equally strong in all parts. "We have met with numerous cases of
this sort, and have called the attention of the builders to the trouble, as the occasions
arose ; but quite recently we met with a boiler right out of the shop of one of the best
builders in the country, and were informed, when we called attention to the defect,
that its importance had been hitherto overlooked in the shop in question. Hence we
coucluded that an article in The Locomotive, calling general attention to the point,
would be timely.
In order to fix the ideas, let us consider the brace shown in the accompanying illus-
tration (Fig. 1), which was recently met with in our work of inspection. The boiler
I
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—
IX
_i_
Fig. 1.— Illustrating Weakness Across Rivet Hole.
B
'/z
THICK
BLADE
from which this was taken was new, and was supposed to be built in accordance with
specifications issued by the Hartford Steam Boiler Inspection and Insurance Company.
These specifications required that each brace should have an area of at least one square
inch, in the weakest part. The body of the brace was round, and 1£ inches in diame-
ter, as indicated in the illustration. If the brace were precisely of the specified diameter
in the body, it would have a sectional area, in that part, of 0.994 sq. in., which is near
enough to the required full square inch to be accepted as conforming to the specifications.
The blade of this brace, however, was only 2\ in. wide and £ in. thick; and it con-
tained two rivet-holes, each || in. in diameter. If the resistance of the brace to fracture
across the line AB, in Fig. 1, is considered, it will be seen that the sectional area here
is much smaller than it is in the body of the brace. The area resisting fracture along
AB is shown by the shaded portions of Fig. 2. The diameter of the rivet-hole being
|| in. (the decimal for which is 0.937 in.), the combined width of the shaded parts is