Reg. 547 a, Reg. 547 b
Fireboxes and Combustion Chambers
(a) Furnaces of vertical boilers
|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 electrical butt-welding.
The welding shall be stress relieved in accordance with
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 welding of the vertical
seams when welded shall be stress relieved.
The maximum permissible variation in diameter, at any
cross section shall not exceed ¼ inch for fireboxes
up to 3 feet in diameter, or 3/8 inch for fireboxes over
3 feet in diameter, or half the thickness of the plate
whichever is the greater.
Circular fireboxes shall preferably be tapered. A taper
of 1½ inches in diameter per foot of height is
recommended. The water space at the bottom between the
firebox and the shell shall be not less than 2 inches
for boilers up to and including 2 feet and 6 inches in
diameter and shall be not less than 2 ½ inches
for boilers over 2 feet and 6 inches in diameter.
The method of welding shall be in accordance with Regulation
Flats formed in the firebox for the insertion of water
tubes shall have an ample radius at the junction of the
flat and the curved surfaces and shall be free from sharp
corners or tool marks. The plate shall not be unduly thinned.
Ogee flanging, whether integral with the firebox or made
as separate ring shall preferably be formed at one heat
by suitable machinery and shall be allowed to cool gradually
to avoid internal stresses.
Rings or firehole mouthpieces or foundation rings shall
be made of mild steel. Z sections shall not be used for
Attachment of fireboxes to cylindrical shells shall be
in accordance with Figures XII/26, XII/27, XII/28
The method of attachment of firehole mouthpieces shall
be in accordance with Figures XII/32
shall be pressed to form by machine in progressive stages
without thinning and shall be annealed on completion.
Methods of attachment of firebox to the shell shall be
in accordance with Figures XII/26, XII/27, XII/28 or
The method of attachment of firehole mouthpieces and throat
pieces shall be in accordance with Figures XII/32,
XII/35 or XII/36.