Register May 2012 No. 677
EXCERPTS FROM: ASME BOILER AND PRESSURE VESSEL CODE
SECTION VIII - RULES FOR CONSTRUCTION OF PRESSURE VESSELS
U-1(a)(1) The Foreword provides the basis for the rules described in this Division.
U-1(a)(2) For the scope of this Division, pressure vessels are containers for the containment of pressure, either internal or external. This pressure may be obtained from an external source, or by the application of heat from a direct or indirect source, or any combination thereof.
U-1(a)(3) This Division contains mandatory requirements, specific prohibitions, and nonmandatory guidance for pressure vessel materials, design, fabrication, examination, inspection, testing, certification, and pressure relief. The Code does not address all aspects of these activities, and those aspects which are not specifically addressed should not be considered prohibited. Engineering judgment must be consistent with the philosophy of this Division, and such judgments must never be used to overrule mandatory requirements or specific prohibitions of this Division. See also informative and nonmandatory guidance regarding metallurgical phenomena in Appendix A of Section II, Part D.
U-1(b) This Division is divided into three Subsections, Mandatory Appendices, and Nonmandatory Appendices. Subsection A consists of Part UG, covering the general requirements applicable to all pressure vessels. Subsection B covers specific requirements that are applicable to the various methods used in the fabrication of pressure vessels. It consists of Parts UW, UF, and UB dealing with welded, forged, and brazed methods, respectively. Subsection C covers specific requirements applicable to the several classes of materials used in pressure vessel construction. It consists of Parts UCS, UNF, UHA, UCI, UCL, UCD, UHT, ULW, and ULT dealing with carbon and low alloy steels, nonferrous metals, high alloy steels, cast iron, clad and lined material, cast ductile iron, ferritic steels with properties enhanced by heat treatment, layered construction, and low temperature materials, respectively. Section II, Part D also contains tables of maximum allowable stress values for these classes of materials.
The Mandatory Appendices address specific subjects not covered elsewhere in this Division, and their requirements are mandatory when the subject covered is included in construction under this Division. The Nonmandatory Appendices provide information and suggested good practices.
U-1(c)(1) The scope of this Division has been established to identify the components and parameters considered in formulating the rules given in this Division. Laws or regulations issued by municipality, state, provincial, federal, or other enforcement or regulatory bodies having jurisdiction at the location of an installation establish the mandatory applicability of the Code rules, in whole or in part, within their jurisdiction. Those laws or regulations may require the use of this Division of the Code for vessels or components not considered to be within its Scope. These laws or regulations should be reviewed to determine size or service limitations of the coverage which may be different or more restrictive than those given here.
U-1(c)(2) Based on the Committee's consideration, the following classes of vessels are not included in the scope of this Division; however, any pressure vessel which meets all the applicable requirements of this Division may be stamped with the Code U Symbol:
(a) those within the scope of other Sections;
(b) fired process tubular heaters;
(c) pressure containers which are integral parts or components of rotating or reciprocating mechanical devices, such as pumps, compressors, turbines, generators, engines, and hydraulic or pneumatic cylinders where the primary design considerations and/or stresses are derived from the functional requirements of the device;
(d) except as covered in U-l(f), structures whose primary function is the transport of fluids from one location to another within a system of which it is an integral part, that is, piping systems;
(e) piping components, such as pipe, flanges, bolting, gaskets, valves, expansion joints, fittings, and the pressure containing parts of other components, such as strainers and devices which serve such purposes as mixing, separating, snubbing, distributing, and metering or controlling flow, provided that pressure containing parts of such components are generally recognized as piping components or accessories;
(f) a vessel for containing water1 under pressure, including those containing air the compression of which serves only as a cushion, when none of the following limitations are exceeded:
- See PDF for table
(1) a design pressure of 300 psi (2 MPa);
(2) a design temperature of 210°F (99°C);
(g) a hot water supply storage tank heated by steam or any other indirect means when none of the following limitations is exceeded:
(1) a heat input of 200,000 Btu/hr (58.6 kW);
(2) a water temperature of 210°F (99°C);
(3) a nominal water containing capacity of 120 gal (450 L);
(h) vessels not exceeding the design pressure, at the top of the vessel, (see 3.2) limitations below, with no limitation on size [see UG-28(f), 9-l(c)]:
(1) vessels having an internal or external pressure not exceeding 15 psi (100 kPa);
(2) combination units having an internal or external pressure in each chamber not exceeding 15 psi (100 kPa) and differential pressure on the common elements not exceeding 15 psi (100 kPa) [see UG-19(a)];
(i) vessels having an inside diameter, width, height, or cross section diagonal not exceeding 6 in. (152 mm), with no limitation on length of vessel or pressure;
U-1(d) The rules of this Division have been formulated on the basis of design principles and construction practices applicable to vessels designed for pressures not exceeding 3000 psi (20 MPa). For pressures above 3000 psi (20 MPa), deviations from and additions to these rules usually are necessary to meet the requirements of design principles and construction practices for these higher pressures. Only in the event that after having applied these additional design principles and construction practices the vessel still complies with all of the requirements of this Division may it be stamped with the applicable Code symbol.
U-1(e) In relation to the geometry of pressure containing parts, the scope of this Division shall include the following:
U-1(e)(1) where external piping; other pressure vessels including heat exchangers; or mechanical devices, such as pumps, mixers, or compressors, are to be connected to the vessel:
(a) the welding end connection for the first circumferential joint for welded connections [see UW-13(g)];
(b) the first threaded joint for screwed connections;
(c) the face of the first flange for bolted, flanged connections;
(d) the first sealing surface for proprietary connections or fittings;
U-1(e)(2) where nonpressure parts are welded directly to either the internal or external pressure retaining surface of a pressure vessel, this scope shall include the design, fabrication, testing, and material requirements established for nonpressure part attachments by the applicable paragraphs of this Division;3
- See PDF for table
U-1(e)(3) pressure retaining covers for vessel openings, such as manhole and handhole covers;
U-1(e)(4) the first sealing surface for proprietary fittings or components for which rules are not provided by this Division, such as gages, instruments, and nonmetallic components.
U-1(f) The scope of the Division includes provisions for pressure relief devices necessary to satisfy the requirements of UG-125 through UG-137 and Appendix 11.
U-1(g)(1) Unfired steam boilers shall be constructed in accordance with the rules of Section I or this Division [see UG- 125(b) and UW-2(c)].
U-1(g)(2) The following pressure vessels in which steam is generated shall not be considered as unfired steam boilers, and shall be constructed in accordance with the rules of this Division:
U-1(g)(2)(a) vessels known as evaporators or heat exchangers;
U-1(g)(2)(b) vessels in which steam is generated by the use of heat resulting from operation of a processing system containing a number of pressure vessels such as used in the manufacture of chemical and petroleum products;
U-1(g)(2)(c) vessels in which steam is generated but not withdrawn for external use.
U-1(h) Pressure vessels or parts subject to direct firing from the combustion of fuel (solid, liquid, or gaseous), which are not within the scope of Sections I, III, or IV may be constructed in accordance with the rules of this Division [see UW-2(d)].
U-1(i) Gas fired jacketed steam kettles with jacket operating pressures not exceeding 50 psi (345 kPa) may be constructed in accordance with the rules of this Division (see Appendix 19).
U-1(j) Pressure vessels exclusive of those covered in U-l(c), U-l(g), U-l(h), and U-l(i) that are not required by the rules of this Division to be fully radiographed, which are not provided with quick actuating closures (see UG-35), and that do not exceed the following volume and pressure limits may be exempted from inspection by Inspectors, as defined in UG-91, provided that they comply in all other respects with the requirements of this Division:
U-1(j)(1) 5 cu ft (0.14 m3) in volume and 250 psi (1.7 MPa) design pressure; or