Maximum Allowable Working Pressure for Nonstandard Pressure Vessels

Maximum Allowable Working Pressure for Nonstandard Pressure Vessels 1. For internal pressure: The maximum allowable working pressure on the shell of a nonstandard pressure vessel 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 diameter of the weakest course and the factor of safety set by these rules. TStE RFS = maximum allowable working pressure, psig where: TS = ultimate tensile strength of shell plate, psi. When the tensile strength of the steel plate is not known, it shall be taken as 55,000 psi for temperatures not exceeding 700% F. t = minimum thickness of shell plate of weakest course, inches. E = efficiency of longitudinal joint depending upon construction. Use the following values: For riveted joints - calculated riveted efficiency; For fusion-welded joints: For riveted joints -- calculated riveted efficiency: For fusion-welded joints: Single lap weld Double lap weld 60 Single butt weld 60 Double butt weld 75 Forge weld Brazed steel R5 inside radius of weakest course of shell, inches, provided the thickness does not exceed 10 percent of the radius. If the thickness is over 10 percent of the radius, the outer radius shall be used. FS5 factor of safety allowed by these rules. 2. For external pressure: The maximum allowable working pressure for cylindrical nonstandard pressure vessels subjected to external or collapsing pressure shall be determined by the rules in Paragraphs UG-28 and UG-29 of Section VIII, Division 1, of the ASME Code. 3. Factors of safety: The minimum factor of safety shall in no case be less than four for existing installations. The factor of safety may be increased when deemed necessary by the inspector to insure the operation of the vessel within safe limits. The condition of the vessel and the particular service of which it is subject. The condition of the vessel and the particular service of which it is subject will be the determining factors. 4. End closures: The maximum allowable working pressure permitted for formed heads under pressure shall be determined by using the appropriate formulas from Paragraphs UG-32, UG-33, or UG-35 of Section VIII, Division 1, ASME Code, and the tensile strength and factors of safety given in Paragraph 2(a), (c).