||The furnaces of vertical boilers
may be constructed in one or more lengthwise sections,
each section being rolled from one plate to a full circle.
In such cases, the component sections may be jointed circumferentially
by electrically butt-welding or riveting. Where welded,
they shall be stress relieved.
||In the case of vertical boilers
where tube plates form part of the firebox, the tube plate
portion may be constructed in two vertical sections and
the vertical seams when welded shall be stress relieved.
||Circular furnaces shall preferably
be tapered, a taper of 1½ inches in diameter per
1 foot of height being recommended. The minimum water
space at the bottom between the furnaces and the shell
shall not be less than 2 inches for boilers upto 2 ft.
6 inches in diameter and shall be not less than 21/2
for boilers over 2 ft. 6 inches in diameter.
||Where hemispherical furnace
crowns are pressed from one plate they shall be pressed
to form by machine in progressive stages without thinning
and on completion shall be annealed.
||Ogee flanging where integral
with the firebox or in a separate ring shall preferably
be formed at one heat by suitable machinery and shall
be allowed to cool gradually to avoid internal stresses.
||Furnaces of vertical type boilers
may be attached to the shell at the firehole by a solid
rectangular section steel ring riveted together or by
a circular ring of substantial section fusion welded to
shell and firebox. Where the latter construction is employed
the opening in the shell for firehole shall be substantially
compensated by a ring welded on the outside of the shell
||At the firehole the firebox
plate and the shell plate may be flanged and fusion welded