THE HONGKONG GOVERNMENT GAZETTE, DECEMBER 3, 1909. 989
APPENDIX.
(1.) The Inspector shall fix the working pressure for boilers, coming in for examina- tion for the first time, by a series of calculations for the strength of the various parts and according to the workmanship and material.
(2.) When boilers are made throughout of irou, or when boilers have certain parts made of iron, tests of such material need not be asked for.
(3.) When steel has been used in the construction of new boilers the Inspector is to for, and obtain if possible, the steel makers' record of the tests as usually issued with terial for boilers.
(4.) Cylindrical Shells:---
The working pressure of the cylindrical shells of steel boilers may be obtained
from the following formula :-
C(T-1) x E D
× E__W
re C-19.7 when the longitudinal seams are fitted with double butt straps of equal width and of a thickness at least equal to that obtained from the formula for butt straps.
C=19.05 when the double butt straps are of unequal width, .e., one strap not
covering the outer row of rivets, with the thickness as before.
C-18.4 when the longitudinal seams are lap joints.
T-Thickness of shell plate, in sixteenths of an inch.
E=The least percentage of strength of longitudinal joints, found as follows:-
For the plate at the joint, E-P-d
For the rivets at the joint, E
where p pitch of rivets, in inches.
d-diameter of rivet holes, in inches.
number of rivets used per pitch.
× 100
p
иха
85, when steel rivets are used. pxt 70, when iron rivets are used.
-sectional area of rivet, in square inches.
t-thickness of plate, in inches.
where rivets are in double shear, a × 1,75 is to be used instead of a.
D-Mean diameter of shell, in inches.
W-Working pressure, in lbs., per square inch.
The constant (C) is to be used with steel of the minimum strength of 26 tons per square inch and not less than 18 per cent. extension in 8 inches; when a higher tensile strength is guaranteed the constant may be proportionately increased up to the maximum tensile for shell plate, viz., 32 tons per square inch.
(5.) Double Butt Straps :-
When all the rows of rivets in the butts are of the same pitch each strap must be at least five-eighths of the thickness of the shell plate and when the pitch of the outer row of rivets is twice that of centre row the thickness of each plate is to be in accordance with the following formula :-
where Ti
5 (p-d)
Ꭲ .
Ti
T
8 (p-2d)
thickness of strap, in sixteenths of an inch.
T -thickness of shell plate, in sixteenths of an inch.
p =pitch of rivets, in inches.
d -diameter of rivet holes, in inches.
(6.) In boilers over seven feet in length the shell circumferential seams are to be at least double riveted, otherwise the working pressure, as found by the formula, may be reduced by four per cent.
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