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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 regulation 562.

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 558.

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 foundation rings.

Attachment of fireboxes to cylindrical shells shall be in accordance with Figures XII/26, XII/27, XII/28 or XII/29.

The method of attachment of firehole mouthpieces shall be in accordance with Figures XII/32 or  XII/33.



(b) Hemispherical fireboxes

Hemispherical fireboxes 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 XII/29.

The method of attachment of firehole mouthpieces and throat pieces shall be in accordance with Figures XII/32, XII/33, XII/35 or XII/36.
 
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