Illinois Administrative Code › Title 41 - FIRE PROTECTION › Part 120 - BOILER AND PRESSURE VESSEL SAFETY › Subpart B - CONSTRUCTION, INSTALLATION, INSPECTION, MAINTENANCE, AND USE › Section 120.300 - Existing Installations of Power Boilers

Current through Register Vol. 48, No. 28, July 12, 2024
Maximum Allowable Working Pressure for Standard Boilers. The
				  maximum allowable working pressure for standard boilers shall be determined in
				  accordance with the applicable provisions of the edition of the ASME Code under
				  which they were constructed and stamped. Existing installations of non-standard
				  power boilers and miniature boilers shall comply with this Section.
a) Maximum Allowable Working Pressure for
				Nonstandard Boilers.
1) 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 from the
				thickness of the plate, the tensile strength of the plate, the efficiency of
				the longitudinal joint or tube ligaments, the inside diameter of the weakest
				course and the factor of safety permitted below.
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Where:
TS = ultimate tensile strength of shell plates, psi.
t = minimum thickness of shell plate, in weakest course,
				  inches.
E = efficiency of longitudinal joint:
For Fusion-Welded and Brazed Joints:
Single lap welded
				  ............................................................... 40
Double lap
				  welded.............................................................. 60
Single butt
				  welded.............................................................. 60
Double butt
				  welded............................................................. 75
Forge
				  welded.......................................................................
				  70
Brazed
				  steel.........................................................................
				  80
For riveted construction, E shall be determined by the rules
				  given in Section I, Part PR, of the 1971 Edition ASME Code.
For seamless construction, E shall be considered 100
				  percent.
R = inside radius of the weakest course of the shell, in
				  inches.
FS = factor of safety permitted.
2) Tensile Strength. When the tensile
				strength of steel or wrought iron shell plates is not known, it shall be taken
				as 55,000 psi for steel and 45,000 psi for wrought iron.
3) Bearing Strength of Mild Steel. The
				resistance to crushing of mild steel shall be taken at 95,000 psi of
				cross-sectional area.
4) Factors of
				Safety. The following factors of safety shall be increased by the Inspector if
				the condition and safety of the boiler demand it: The lowest factor of safety
				permissible on existing installations shall be 5, except for horizontal return
				tubular boilers having continuous longitudinal lap seams more than 12 ft. in
				length, when the factor of safety shall be 8; when this latter type of boiler
				is removed from its existing setting, it shall not be reinstalled for pressures
				in excess of 15 psig. Reinstalled or second-hand boilers shall have a minimum
				factor of safety of 6 when the longitudinal seams are of lap riveted
				construction, and a minimum factor of safety of 5 when the longitudinal seams
				are of butt and double-strap construction.