scope:

Overview

In 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 as a result of a process, or any combination thereof.

The rules of this Division may be used for the construction of the following pressure vessels.

a) Vessels to be installed at a fixed (stationary) location for a specific service where operation and maintenance control is retained during the useful life of the vessel by the user and is in conformance with the User's Design Specification required by Part 2.

b) Pressure vessels installed in ocean-going ships, barges, and other floating craft or used for motor vehicle or rail freight. For these applications it is necessary that prior written agreement with the jurisdictional authority be established covering operation and maintenance control for a specific service. This operation and maintenance control must be retained during the useful life of the pressure vessel by the user in conformance with the User's Design Specification required in Part 2. Such a pressure vessel as described above may be constructed and stamped within the scope of this Division provided it meets all other requirements as specified with the following additional provisions.

1) Loading conditions imposed by movement of the pressure vessel during operation and by relocation of the pressure vessel between work sites or due to loading and discharge, as applicable, shall be considered in the design.

2) The User's Design Specification shall include the agreements that define those aspects of operation and maintenance control unique to the particular pressure vessel.

c) Pressure vessels or parts subject to direct firing from the combustion of fuel (solid, liquid, or gaseous), that are not within the scope of Sections I, III, or IV may be constructed in accordance with the rules of this Division.

d) Unfired steam boilers shall be constructed in accordance with the rules of Section I or Section VIII, Division 1.

e) The following pressure vessels in which steam is generated shall be constructed in accordance with the rules of Section VIII, Division 1 or this Division:

1) Vessels known as evaporators or heat exchangers;

2) 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; and

3) Vessels in which steam is generated but not withdrawn for external use.

The scope of this Division has been established to identify 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 the 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.

Additional Requirements for Very High Pressure Vessels

The rules of this Division do not specify a limitation on pressure but are not all-inclusive for all types of construction. For very high pressures, some additions to these rules may be necessary to meet the design principles and construction practices essential to vessels for such pressures. However, only in the event that, after application of additional design principles and construction practices, the vessel still complies with all of the requirements of the Code, may it be stamped with the Code symbol.

As an alternative to this Division, Section VIII, Division 3 should be considered for the construction of vessels intended for operating pressures exceeding 68.95 MPa (10,000 psi).

Geometric Scope of This Division

The scope of this Division is intended to include only the vessel and integral communicating chambers, and shall include the following:

a) Where external piping, other pressure vessels including heat exchangers, or mechanical devices (i.e. pumps, mixers, or compressors) are to be connected to the vessel:

1) The welding end connection for the first circumferential joint for welded connections (see Table 4.2.4).

2) The first threaded joint for screwed connections.

3) The face of the first flange for bolted and flanged connections. Optionally, when the first flange is welded to the nozzle neck, the weld connecting the flange to the nozzle neck may be considered as the first circumferential joint, provided this construction is documented in the User's Design Specification and is properly described on the vessel drawing and the Manufacturer's Data Report Form.

4) The first sealing surface for proprietary connections or fittings.

b) Where nonpressure parts are welded directly to either the internal or external pressure retaining surface of a pressure vessel, the scope of this Division shall include the design, fabrication, testing, and material requirements established for nonpressure part attachments by the applicable paragraphs of this Division (see paragraph 4.2.5.6).

c) Pressure retaining covers and their fasteners (bolts and nuts) for vessel openings, such as manhole and handhole covers.

d) The first sealing surface for proprietary connections, fittings or components that are designed to rules that are not provided by this Division, such as gages, instruments, and nonmetallic components.

Classifications Outside the Scope of this Division

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 a Jurisdictional Authority at the location of an installation establish the mandatory applicability of the Code rules, in whole or in part, within that 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 that may be more restrictive than those given here. 

The following vessels are not included in the scope of this Division. However, any pressure vessel, with the exception of (a) below, that is not excluded from the scope of this Division by paragraph 1.2.1.2 and that meets all applicable requirements of this Division may be stamped with the U2 Code symbol.

a) Vessels within the scope of other Sections.

b) Fired process tubular heaters as defined in API RP560.

c) Pressure containers that 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) Structures consisting of piping components, such as pipe, flanges, bolting, gaskets, valves, expansion joints, and fittings 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, including the piping system between a pressure relief device and the vessel it protects, see Part 9.

e) Pressure containing parts of components, such as strainers and devices that 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 water under pressure, including those containing air the compression of which serves only as a cushion, when none of the following limitations are exceeded:

1) A design pressure of 2.07 MPa (300 psi)

2) A design temperature of 99°C (210°F)

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 58.6 kW (200,000 Btu/hr)

2) A water temperature of 99°C (210°F)

3) A nominal water containing capacity of 454 liters (120 gal)

h) Vessels with an internal or external design pressure not exceeding 103 kPa (15 psi) with no limitation on size, for multi-chambered vessels, the design pressure on the common elements shall not exceed 103 kPa (15 psi).

i) Vessels with an inside diameter, width, height, or cross section diagonal not exceeding 150 mm (6 inches), with no limitation on length of vessel or pressure.

j) Pressure vessels for human occupancy (requirements for pressure vessels for human occupancy are covered in ASME PVHO-1).

Combination Units

When a pressure vessel unit consists of more than one independent pressure chamber, only the parts of chambers that come within the scope of this Division need be constructed in compliance with its provisions (see Part 4, paragraph 4.1.8).

Field Assembly of Vessels

Field assembly of vessels constructed to this Division may be performed as follows.

a) The Manufacturer of the vessel completes the vessel in the field, completes the Form A-1 Manufacturer's Data Report, and stamps the vessel.

b) The Manufacturer of parts of a vessel to be completed in the field by some other party stamps these parts in accordance with Code rules and supplies the Form A-2 Manufacturer's Partial Data Report to the other party. The other party, who must hold a valid U2 Certificate of Authorization, makes the final assembly, performs the required NDE, performs the final pressure test, completes the Form A-1 Manufacturer's Data Report, and stamps the vessel.

c) The field portion of the work is completed by a holder of a valid U2 Certificate of Authorization other than the vessel Manufacturer. The stamp holder performing the field work is required to supply a Form A-2 Manufacturer's Partial Data Report covering the portion of the work completed by his organization (including data on the pressure test if conducted by the stamp holder performing the field work) to the Manufacturer responsible for the Code vessel. The vessel Manufacturer applies his U2 Stamp in the presence of a representative from his Inspection Agency and completes the Form A-1 Manufacturer's Data Report with his Inspector.

In all three alternatives, the party completing and signing the Form A-1 Manufacturer's Data Report assumes full Code responsibility for the vessel. In all three cases, each Manufacturer's Quality Control System shall describe the controls to assure compliance by each Code stamp holder.

Pressure Relief Devices

The scope of this Division includes provisions for pressure relief devices necessary to satisfy the requirements of Part 9.