North Dakota Administrative Code › Title 33.1 - Department of Environmental Quality › Article 33.1-14 - NORTH DAKOTA BOILER RULES › Chapter 33.1-14-05 - POWER BOILERS - EXISTING INSTALLATIONS › Section 33.1-14-05-02 - Maximum allowable working pressure for nonstandard boilers

Current through Supplement No. 393, July, 2024
1. The maximum allowable working pressure on
				the shell of a nonstandard boiler must 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
				allowed by this article.
TStE = Maximum allowable working pressure, per square inch
				  gauge where: RFS
TS = Ultimate tensile strength of shell plates per square
				  inch
t = Minimum thickness of shell plate, in weakest course,
				  inches
E = Efficiency of longitudinal joint:
For tube ligaments and riveted construction, E shall be
				  determined by the rules given in section I, part PR, of the American Society of
				  Mechanical Engineers Code for power boilers. For seamless construction, E shall
				  be considered one hundred percent.
R = Inside radius of the weakest course of the shell, in
				  inches
FS = Factor of safety permitted
2. When the tensile strength of steel or
				wrought iron shell plate is not known, it must be taken as fifty-five thousand
				pounds per square inch [386.11 megapascals] for steel and forty-five thousand
				pounds per square inch [310.26 megapascals] for wrought iron.
3. The resistance to crushing of mild steel
				must be taken at ninety-five thousand pounds per square inch [655 megapascals]
				of the cross-sectional area.
4.
				When computing the ultimate strength of rivets in shear, the following values,
				in pounds per square inch [megapascals] of the cross-sectional area of the
				rivet shank must be used:
POUNDS PER SQUARE INCH
MEGAPASCALS
Iron rivets in single shear
38,000
262.00
Iron rivets in double shear
76,000
524.00
Steel rivets in single shear
44,000
303.37
Steel rivets in double shear
88,000
606.69
When the diameter of the rivet holes in the longitudinal
				  joints of a boiler is not known, the diameter and cross-sectional area of
				  rivets, after driving, may be selected from the following table, or as
				  ascertained by cutting out one rivet in the body of the joint.
SIZES OF RIVETS BASED ON PLATE THICKNESS
Thickness of plate, inches
1/4
9/32
5/16
11/32
3/8
13/32
Diameter of rivet after driving, inches
11/16
11/16
3/4
3/4
13/16
13/16
Thickness of plate, inches
7/16
15/32
1/2
9/16
5/8
Diameter of rivet after driving, inches
15/16
15/16
15/16
1-1/16
1-1/16
5.
				The following factors of safety must be increased by the inspector if the
				condition and safety of the boiler demand it:
a. The lowest factor of safety permissible on
				existing installations is four, except for horizontal-return-tubular boilers
				having continuous longitudinal lap seams more than twelve feet [3.66 meters] in
				length, when the factor of safety is eight; when this latter type boiler is
				removed from its existing setting, it may not be reinstalled for pressures in
				excess of fifteen pounds per square inch gauge [103 kilopascals].
b. Reinstalled or secondhand boilers must
				have a minimum factor of safety of six when the longitudinal seams are of
				lap-riveted construction, and a minimum factor of safety of five when the
				longitudinal seams are of butt-and-double-strap construction. Steam traction
				engines must be considered as secondhand boilers for purposes of determining
				their factors of safety.