+
K
THE HONGKONG GOVERNMENT GAZETTE, DECEMBER 3, 1909.
991
(9.) When the top of fire boxes are supported by solid iron girders of rectangular section and are not subjected to a greater temperature than the ordinary heat of steam, the following formula may be employed:--
Cx d2 x T (WP) DxL
W
where W-width of combustion box in inches.
P-pitch of supporting bolts in inches.
D-distance between the girders from centre to centre in inches.
L-length of the girder in feet. d=depth of the girder in inches. T-thickness of girder in inches. N-number of supporting bolts.
N × 1,000
C
when the number of boits is odd.
(=
when the number of bolts is even
N+1 (N+1) 1,000,
N+2
W-working pressure.
The working pressure for the supporting bolts and for the plate between them should be determined by the rules for ordinary stays and plates.
When the girders are formed from steel plates the constant may be increased fifteen
per cent.
(10.) The working pressure allowed on steel dished ends may be ascertained by the following formula :---
where W
Working pressure.
S×4 × TX D
R2 + D2
W
S=6,500 (stress allowed per square inch of section).
T Thickness of plate in inches.
D-Depth of camber (internal)
R: Radius of circular base of plate.
Dished ends in compression may be calculated by the above formula but S-4,000. When dished ends are of iron S is to be reduced 24 per cent.
Hemispherical ends may be allowed double the working pressure given to a cylinder of the same diameter and thickness, but the ends are to be formed of not less than four pieces.
The dished ends of vertical boilers having an uptake joining crown of firebox and top of boiler, if equal to the required pressure when considered as portions of spheres, will require to be stayed, but the stays may, if of iron, be allowed a pressure of 16,000 lbs. per square inch of nett section and if of steel 20,000 lbs. per square inch of nett section.
(11.) The neutral portions of boiler shells under steam domes will require to be efficiently stiffened or stayed.
(12.) Compensating rings should be fitted round all manhole and handhole openings in boilers equal in section to the portion cut out, such compensating rings not to be less in thickness than the plate they cover.
(13.) Boilers coming in for inspection for the first time should be tested by hydraulic pressure to at least one and three-quarter times and not more than twice the working pressure, ascertained after inspection and calculation.
(14.) In calculating the working pressure of steel circular furnaces of a length not exceeding ten feet the following formula may be used:—
where T-thickness in inches.
105,000 × T
(L+1) D
W
L-length in feet (between rings or hoops if fitted).
D-outside diameter in inches.
W-working pressure.
provided W does not exceed
10,500 × T
No comments yet.
Private notes are available after approval.