he loss due to the infiltration
of air, which may amount to an additional five per cent., as compared
with brick settings that are not maintained in good order. Steel plate,
or steel plate backed by asbestos mill-board, while acting as a
preventative against the infiltration of air through the boiler setting,
is not as effective from the standpoint of decreasing radiation losses
as a casing properly insulated from the brick portion of the setting by
magnesia block and asbestos mill-board. A casing which has been found to
give excellent results in eliminating air leakage and in the reduction
of radiation losses is clearly illustrated on page 306.

Many attempts have been made to use some material other than brick for
boiler settings but up to the present nothing has been found that may be
considered successful or which will give as satisfactory service under
severe conditions as properly laid brickwork.

BOILER ROOM PIPING

In the design of a steam plant, the piping system should receive the
most careful consideration. Aside from the constructive details, good
practice in which is fairly well established, the important factors are
the size of the piping to be employed and the methods utilized in
avoiding difficulties from the presence in the system of water of
condensation and the means employed toward reducing radiation losses.

Engineering opinion varies considerably on the question of material of
pipes and fittings for different classes of work, and the following is
offered simply as a suggestion of what constitutes good representative
practice.

All pipe should be of wrought iron or soft steel. Pipe at present is
made in "standard", "extra strong"[76] and "double extra strong"
weights. Until recently, a fourth weight approximately 10 per cent
lighter than standard and known as "Merchants" was built but the use of
this pipe has largely gone out of practice. Pipe sizes, unless otherwise
stated, are given in terms of nominal internal diameter. Table 62 gives
the dimensions and some general data on standard and extra strong
wrought-iron pipe.

TABLE 62

DIMENSIONS OF STANDARD AND EXTRA STRONG[76]
WROUGHT-IRON AND STEEL PIPE

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| | Diameter | Circumference |
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