A. Model steam boilers are subject to the requirements of Regulations .01, .01-1, .05, .08, .09, .14.16, .19, and .27.31 of this chapter.
C. A model steam boiler may not be operated in Maryland unless it has a valid:
(1) Maryland inspection certificate; or
(2) Inspection or operating certificate issued by another state having standards equivalent to the requirements of this regulation.
D. Inspection Certificate.
(1) Unless sooner suspended or revoked, an inspection certificate expires 1 year from date of issuance.
(2) An inspection certificate shall specify the maximum operating pressure of the model steam boiler, determined in accordance with this regulation.
E. Initial Test.
(1) Before an initial test of a model steam boiler:
(a) An owner shall provide the inspector with:
(i) Construction drawings,
(ii) Material specifications,
(iii) Welding and brazing information,
(iv) Stress calculations, in accordance with §H of this regulation,
(v) The calculated factor of safety,
(vi) Requested maximum operating pressure,
(vii) The name and qualifications of the manufacturer and assembler, and
(viii) The name and qualifications of the designer, if available; and
(b) An inspector shall verify that the design of the model steam boiler is in accordance with the documents provided.
(2) Before being put into operation, a new model steam boiler shall be tested hydrostatically to a pressure of at least two times the maximum operating pressure.
(1) A model steam boiler shall be tested:
(a) Annually; and
(b) After repair or modification.
(2) An owner requesting an inspection of a model steam boiler shall supply test equipment, including:
(a) Water source, pump, pressure lines, and master test gage; and
(b) Plugs, gags, or caps to replace safety valves or other appurtenances, if needed to prevent damage by the required test pressure.
(3) An inspector:
(a) Shall conduct an external inspection and, to the extent possible, an internal inspection, to ascertain the physical condition of the model steam boiler before the hydrostatic test is conducted;
(b) Shall witness the hydrostatic test;
(c) May require that:
(i) A model steam boiler be placed in operation so the inspector can make further observations and check safety valve operation, and
(ii) An accumulation test be conducted in accordance with Regulation .24J(1)(a) of this chapter; and
(d) If the test is completed successfully, shall sign the test report and file it with the chief boiler inspector.
(4) A hydrostatic test:
(a) Except as otherwise provided by this regulation, shall be applied at 1-1/2 times the maximum operating pressure;
(b) May be conducted using a model steam boiler's feed pump and pressure gage, if the:
(i) Range of the gage is sufficient, and
(ii) Gage has been calibrated in accordance with this regulation; and
(c) May not be approved if the model steam boiler:
(i) Shows leakage, bulging or displacement of a sheet, firebox, barrel, or other surface exposed to pressure, or
(ii) While pressure is being increased or is at the maximum level, experiences a serious leak, unusual sound, or sudden drop in pressure.
(1) Safety Valve.
(a) A model steam boiler shall have two or more safety valves.
(b) Each safety valve shall be set at or below the maximum operating pressure.
(c) A model steam boiler shall:
(i) Have sufficient safety valve capacity to discharge all steam the model steam boiler can generate, without allowing pressure to rise more than 6 percent above the maximum operating pressure; and
(ii) Comply with the requirements of the ASME Code, Section I, Paragraph PG-70.
(2) Steam Gage. If a steam gage:
(a) Has sufficient range:
(i) It may be left in place during a test,
(ii) A record shall be made of its readings and compared with the master test gage, and
(iii) If test readings conflict, the steam gage shall be recalibrated or replaced;
(b) Does not have sufficient range for test pressure:
(i) The steam gage shall be removed and calibrated with the test gage or with a dead weight tester, and
(ii) A test gage shall be used to conduct the test.
H. Maximum operating pressure, as designated on the inspection certificate:
(1) For a model steam boiler on a locomotive, shall be that necessary to move the locomotive, considering cylinder dimension and weight on driving wheels;
(2) For other model steam boilers, shall be that necessary for optimum operation of the engine; and
(3) May not exceed the maximum allowable working pressure.
I. Maximum Allowable Working Pressure.
(1) Maximum allowable working pressure on:
(a) The shell of a model steam boiler shall be computed by the formula: (s X t X c)/r = maximum allowable working pressure, PSIG, where:
(i) s = maximum allowable material stress, PSI,
(ii) t = minimum thickness of the shell wall, in inches,
(iii) c = constant, which for a seamless shell shall be 1.0, and for a welded shell shall be 0.8, and
(iv) r = outside radius of the shell, in inches;
(b) A stayed surface shall be computed by the formula: (t squared X s X c)/p squared = Maximum allowable working pressure, PSIG, where:
(i) c = constant, which for welded or silver soldered stay bolts without heads shall be 2.1, and for welded or silver soldered stay bolts with heads shall be 2.8,
(ii) p = stay bolt pitch, in inches, using the largest dimension if the spacing is not square,
(iii) s = maximum allowable material stress, PSI, and
(iv) t = minimum thickness of the wall, in inches;
(c) A stay bolt shall be computed by the formula: (a X s)/(h X v) = maximum allowable working pressure, PSIG, where:
(i) a = cross sectional area of stay bolt, root of thread, if threaded, in square inches,
(ii) h = stay bolt horizontal spacing, in inches,
(iii) s = maximum allowable material stress, PSI, and
(iv) v = stay bolt vertical spacing, in inches.
(2) The calculated factor of safety shall be computed by the formula: ((maximum allowable ASME Code calculated working pressure, PSIG)/(maximum operation pressure, PSIG)) X (ASME Code factor of safety) = calculated factor of safety
(3) The maximum allowable material stress shall be, for:
(a) Carbon steel:
(i) Ultimate tensile strength: 50,000 PSI;
(ii) ASME Code factor of safety: 4;
(iii) Allowable working stress: 12,500 PSI; and
(iv) A temperature allowance is not required for pressures up to 250 PSI. Allowable stress values for pressures above 250 PSI shall comply with the requirements of the ASME Code, Section I, Part PG-23.
(i) Ultimate tensile strength: 30,000 PSI;
(ii) ASME Code factor of safety: 5; and
(iii) Allowable working stress, with temperature allowance:
Atmospheric, 40° to 100°F ... 6,000 PSI
80 PSIG, 324°F ... 4,400 PSI
90 PSIG, 331°F ... 4,300 PSI
100 PSIG, 338°F ... 4,200 PSI
110 PSIG, 344°F ... 4,100 PSI
120 PSIG, 350°F ... 4,000 PSI