Code of Maryland Regulations (Last Updated: April 6, 2021) |
Title 09. Maryland Department of Labor |
Subtitle 12. DIVISION OF LABOR AND INDUSTRY |
Chapter 09.12.01. Board of Boiler Rules |
Sec. 09.12.01.22. Power Boiler — Existing Installation: Maximum Allowable Working Pressure
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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:
Rivet Size Plate Thickness
in InchesRivet 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.