# COMAR Title 09 — Maryland Department of Labor

## Subtitle 12 — Division of Labor and Industry

### Chapter 01 — Board of Boiler Rules

#### Regulation .22 Power Boiler — Existing Installation: Maximum Allowable Working Pressure.

*COMAR 09.12.01.22*

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:

  (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:

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.