Section 680IAC2-11-2. Maximum allowable working pressure for nonstandard unfired pressure vessels

   (a) The maximum allowable working pressure for nonstandard unfired pressure vessels, for which data are available evidencing they have been so designed and constructed as to be substantially equivalent to standard pressure vessels except for the stamping, shall be determined on the same basis as for standard pressure vessels.

  (b) The maximum allowable working pressure for a nonstandard pressure vessel not covered by subsection (a) shall be the least of the values found for allowable working pressure for any of the essential parts of the vessel (such as shell, heads, or nozzle openings) by the principles given in this subsection or subsection (c) and section 3 of this rule as adjusted for any difference in static head that may exist between the part considered and the top of the vessel.

(1) For internal pressure, the allowable working pressure for the shell of nonstandard cylindrical pressure vessels such as considered in this subsection shall be determined by the strength of the weakest course computed from the thickness of the plate, the tensile strength of the plate, the efficiency of the longitudinal joint, the inside radius of the course, and the factor of safety allowed under section 3 of this rule. The equation shall be:

Where:	P	=	Allowable working pressure in psig for the shell.
	TS	=	Ultimate tensile strength of shell material in pounds per square inch. For carbon steel plates, when the tensile strength is not known, it shall be taken as fifty-five thousand (55,000) psi for temperatures not exceeding seven hundred degrees Fahrenheit (700°F). Where the tensile strength of cast iron is not known, it shall be taken to be twenty thousand (20,000) psi.
	t	=	Minimum thickness of shell plate of weakest course, in inches. When the contents of a vessel are corrosive, it shall be taken as the last measured minimum thickness minus twice the thickness expected to be lost by corrosion before the next inspection.
	E	=	Efficiency of longitudinal joint depending upon construction. Use values as follows:
				For seamless shells: E = 1.
				For riveted joints: calculated joint efficiency.
				For fusion welded, forge welded, or brazed joints:
				Fusion single lap weld	40%
				Fusion double lap weld	60%
				Fusion single butt weld	50%
				Fusion double butt weld	70%
				Forge weld	70%
				Brazed steel	80%
				Brazed copper	90%
				Vessels with brazed joints shall not be operated with metal temperatures in excess of four hundred six degrees Fahrenheit (406°F).
	R	=	Inside radius of weakest course of shell, in inches, provided the thickness does not exceed ten percent (10%) of the radius. If the thickness is over ten percent (10%) of the radius, the outer radius shall be used.
	FS	=	Factor of safety allowed by this section.

(2) The allowable working pressure for heads of nonstandard pressure vessels such as considered in this subsection shall be determined by the applicable formulas in the API-ASME code or Section VIII of the ASME code, based on the last measured minimum thickness of the head in question or, in the case of heads, subject thickness expected to be lost by corrosion before the next inspection. Efficiencies for joints in a head shall be taken to be the same as specified in subdivision (1) for shell joints. The joints, in a head, shall be taken to be the same as specified in subdivision (1) for shell joints. The joint efficiencies are to be used in the head formulas only to the extent that the heads themselves actually contain a joint or joints, as distinguished from the joint between the head and shell; however, a determination also shall be made as to whether the strength of the joint between the head and shell is adequate to withstand the pressure imposed on the projected area of the head (namely, 3.14 PR²), based on the least thickness of head or shell plate adjacent to such joint and the applicable joint efficiency specified in subdivision (1); and if the strength of this joint fails to meet this criterion, the allowable working pressure for the head (as determined by the applicable head formula) shall be reduced accordingly.

(3) The allowable working pressure for a shell course, or head, in which there is any opening larger than two (2) inch pipe size in the solid plate (or larger than three (3) inch pipe size if the net thickness of the plate, after deducting corrosion allowance, is three-eighths (⅜) inch or less) and which has no more reinforcement for such opening than that inherent in the manway or nozzle neck and its attachment welds, shall be taken to be sixty percent (60%) of the allowable working pressure computed for a seamless shell course, or head, of the same dimensions, using in such computations the last measured thickness of the vessel element in question minus twice the thickness expected to be lost by corrosion before the next inspection. Or, alternatively, the effect of such opening on the allowable working pressure for such shell course, or head, shall be computed in accordance with applicable provisions of the API-ASME code or Section VIII of the ASME code using the dimensions of the materials actually available for reinforcement of such opening after deducting corrosion allowance as established in this subsection.

(4) For conditions not covered in this subsection, applicable provisions of the API-ASME code or Section VIII in the ASME code shall apply, or the case may be referred to the chief inspector for instruction concerning the requirements.

  (c) The maximum allowable working pressure for cylindrical vessels subjected to external or collapsing pressure shall be determined by the applicable rules of the API-ASME code or Section VIII of the ASME code. (Boiler and Pressure Vessel Rules Board; 680 IAC 2-11-2; filed Jan 5, 1996, 10:15 a.m.: 19 IR 1137; 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)