Section 680IAC2-8-2. Maximum allowable working pressure for nonstandard boilers

   (a) The maximum allowable working pressure on the shell of a nonstandard boiler or drum 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 outside course, and the factor of safety allowed by this section. The equation shall be:

Where:	P	=	Maximum allowable working pressure, in psig.
	TS	=	Ultimate tensile strength of shell plates, in psi.
	t	=	Minimum thickness of shell plate, in weakest course, in inches.
	E	=	Efficiency of longitudinal joint or tube hole ligaments, whichever is less. For riveted construction, E shall be determined by the methods illustrated in Section I of the ASME code (1971 edition). For tube hole ligaments, E shall be determined by the rules in Section I of the ASME code.
	R	=	One-half (½) the inside diameter of the weakest course of shell or drum in inches.
	FS	=	Factor of safety permitted.

  (b) When the tensile strength of steel or wrought iron shell plates is not known, it shall be taken as fifty-five thousand (55,000) psi for steel and forty-five thousand (45,000) psi for wrought iron.

  (c) The resistance to crushing of mild steel shall be taken as ninety-five thousand (95,000) psi for each square inch of cross-sectional area.

  (d) When computing the ultimate strength of rivets in shear, the following values in psi of the cross-sectional area of the rivet shank shall be used:

Iron rivets in single shear38,000

Iron rivets in double shear76,000

Steel rivets in single shear44,000

Steel rivets in double shear88,000

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 by cutting out one (1) rivet in the body of the joint, or as follows:

SIZES OF RIVETS BASED ON PLATE THICKNESS

¼ʺ t (11/16ʺ rivet)

9/32ʺ t (11/16ʺ rivet)

5/16ʺ t (¾ʺ rivet)

11/32ʺ t (¾ʺ rivet)

3/8ʺ t (13/16ʺ rivet)

13/32ʺ t (13/16ʺ rivet)

7/16ʺ t (15/16ʺ rivet)

15/32ʺ t (15/16ʺ rivet)

½ʺ t (15/16ʺ rivet)

9/16ʺ t (17/16ʺ rivet)

5/8ʺ t (17/16ʺ rivet).

Rivet size is based on diameter after driving.

  (e) The following factors of safety shall be increased based on an extrapolation of them as a function of the age and condition of the boiler:

(1) The lowest factor of safety permissible on existing nonstandard installations shall be four and one-half (4½) excepting for horizontal return tubular boilers having continuous lap seams more than twelve (12) feet in length where the factor of safety shall be eight (8), and, when this latter type of boiler is removed from its existing setting, it shall not be reinstalled for pressures in excess of fifteen (15) psig.

(2) Reinstalled or secondhand boilers shall have a minimum factor of safety of six (6) when the longitudinal seams are of lap riveted construction, and a minimum factor of safety of five (5) when the longitudinal seams are of butt and double strap construction.

  (f) The age limit of a horizontal return tubular, flue, or cylinder boiler having a longitudinal lap joint and operating at a pressure in excess of fifty (50) psig shall be thirty (30) years. A variance from this may be granted by the rules board as set forth at IC 22-12-2-11 [sic.] and rule 2 of this article [sic., 680 IAC 2-2]. (Boiler and Pressure Vessel Rules Board; 680 IAC 2-8-2; filed Jan 5, 1996, 10:15 a.m.: 19 IR 1128; readopted filed Jul 9, 2001, 1:33 p.m.: 24 IR 3822; readopted filed Sep 21, 2007, 9:16 a.m.: 20071010-IR-680070389RFA; readopted filed Oct 19, 2007, 1:08 p.m.: 20071114-IR-680070389RFA; readopted filed Sep 5, 2013, 10:09 a.m.: 20131009-IR-680130182RFA)