Current through Register Vol. 50, No. 25, December 15, 2023
A. The
maximum allowable working pressure on a standard boiler shall be determined in
accordance with the ASME Code under which it was constructed and
stamped.
B. The maximum allowable
working pressure on the shell of a nonstandard boiler shall be determined by
the strength of the weakest section of the structure computed by multiplying TS
by t and E and dividing the product by R multiplied by FS:
(TS x t x E) / (R x FS) = maximum allowable working pressure,
PSIG, where:
(1) TS = ultimate tensile
strength of the shell plate, PSI, which, if unknown, shall be:
(a) 55,000 PSI for steel; and
(b) 45,000 PSI for wrought iron;
(2) t = minimum thickness of the
shell plate of the weakest course, in inches;
(3) E = efficiency of the longitudinal joint,
which is, for:
(a) Tube ligaments and riveted
construction, established by Section I of the ASME Code for power boilers;
and
(b) Seamless construction, 100
percent;
(4) R = inside
radius of the weakest course of the shell, in inches;
(5) FS = factor of safety required by this
regulation;
(6) The resistance to
crushing of mild steel is assumed to be 95,000 PSI of cross-sectional
area;
(7) When computing the
ultimate strength of rivets in shear, the following values, in pounds per
square inch, of the cross-sectional area of the rivet shank shall be used:
(a) Iron rivets in single shear 38,000
PSI;
(b) Iron rivets in double
shear 76,000 PSI;
(c) Steel rivets
in single shear 44,000 PSI; and
(d)
Steel rivets in double shear 88,000 PSI;
(8) When the diameter of a rivet hole in a
longitudinal joint of a boiler is not known, the diameter and cross-sectional
area of the rivet, after driving, shall be:
(a) Ascertained by cutting out one rivet in
the body of the joint; or
(b) As
indicated in the following table:
| Plate Thickness in Inches |
Rivet Diameter |
| 1/4 |
11/16 |
| 9/32 |
11/16 |
| 5/16 |
3/4 |
| 11/32 |
3/4 |
| 3/8 |
13/16 |
| 13/32 |
13/16 |
| 7/16 |
15/16 |
| 15/32 |
15/16 |
| 1/2 |
15/16 |
| 9/16 |
1-1/16 |
| 5/8 |
1-1/16 |
C. The maximum allowable working pressure on
a:
(1) Water-tube boiler having tubes secured
to cast iron or malleable-iron headers, or having cast-iron mud drums, shall be
160 PSIG;
(2) Cast-iron boiler,
except a hot-water boiler, shall be 15 PSIG;
(3) Boiler having lap-riveted longitudinal
joints, operated at a pressure greater than 50 PSI, when removed from an
existing setting and reinstalled, shall be 15 PSIG; and
(4) Reinstalled horizontal-return tubular
boiler having a continuous longitudinal lap seam more than 12 feet long, shall
be 15 PSIG.
D. Except as
otherwise provided by this regulation, the lowest factor of safety shall be,
for:
(1) An existing installation:
4.5;
(2) A horizontal-return
tubular boiler having continuous longitudinal lap seams more than 12 feet long:
8;
(3) A reinstalled or secondhand
boiler having longitudinal seams of lap-riveted construction: 6; and
(4) A reinstalled or secondhand boiler with
longitudinal seams of butt and double-strap construction: 5.
Regulations .22 adopted
effective June 1, 1989 (16:10 Md. R. 1106)
Regulation .22B amended
effective July 3, 1995 (22:13 Md. R. 966)
