ASME/BPVC SEC III-1 NB

SECTION III DIVISION 1 - SUBSECTION NB CLASS 1 COMPONENTS RULES FOR CONSTRUCTION OF NUCLEAR FACILITY COMPONENTS

Year: 2013

Abstract: ASPECTS OF CONSTRUCTION COVERED BY THESE RULES
(a) Subsection NB contains rules for the material, design, fabrication, examination, testing, overpressure relief, marking, stamping, and preparation of reports by the Certificate Holder of items which are intended to conform to the requirements for Class 1 construction.
(b) The rules of Subsection NB cover the requirements for strength and pressure integrity of items, the failure of which would violate the pressure-retaining boundary. The rules cover initial construction requirements, but do not cover deterioration which may occur in service as a result of corrosion, radiation effects, or instability of material. NCA-1130 gives further limitations to the rules of this Subsection.
TEMPERATURE LIMITS
The rules of Subsection NB shall not be used for items which are to be subjected to metal temperatures that exceed the temperature limit in the applicability column shown in Section II, Part D, Subpart 1, Tables 2A, 2B, and 4 for design stress intensity values. Above those temperatures, the creep and stress rupture characteristics of materials permitted to be used become significant factors which are not presently covered by the rules of this Subsection. Fatigue design curves and specified methods for fatigue analysis are not applicable above 700°F (370°C) for materials covered by Figs. I-9.1 and I-9.4, and above 800°F (425°C) for materials covered by Figs. I-9.2 and I-9.3.
BOUNDARIES OF JURISDICTION APPLICABLE TO THIS SUBSECTION
Boundary of Components
The Design Specification shall define the boundary of a component to which piping or another component is attached. The boundary shall not be closer to a vessel, tank, pump, or valve than:
(a) the first circumferential joint in welded connections (the connecting weld shall be considered part of the piping);
(b) the face of the first flange in bolted connections (the bolts shall be considered part of the piping);
(c) the first threaded joint in screwed connections.
Boundary Between Components and Attachments
Attachments
(a) An attachment is an element in contact with or connected to the inside or outside of the pressure-retaining portion of a component.
(b) Attachments may have either a pressure-retaining or a nonpressure-retaining function.
(1) Attachments with a pressure-retaining function include items such as pressure boundary stiffeners, and branch pipe and vessel opening reinforcement.
(2) Attachments with a nonpressure-retaining function include items such as:
(a) valve guides, thermal sleeves, and turning vanes
(b) core support structures, internal structures, or other permanent structures within the reactor pressure vessel; and
(c) vessel saddles, support and shear lugs, brackets, pipe clamps, trunnions, skirts, and other items in the support load path.
(c) Attachments may also have either a structural or nonstructural function.
(1) Attachments with a structural function (structural attachments):
(a) perform a pressure-retaining function;
(b) are core support structures, internal structures, or other permanent structures within the reactor pressure vessel; or
(c) are in the support load path.
(2) Attachments with a nonstructural function (nonstructural attachments):
(a) do not perform a pressure-retaining function;
(b) are not in the support load path;
(c) may be permanent or temporary.
Nonstructural attachments include items such as nameplates, insulation supports, and locating and lifting lugs.
Jurisdictional Boundary.
The jurisdictional boundary between a pressure-retaining component and an attachment defined in the Design Specification shall not be any closer to the pressure-retaining portion of the component than as defined in (a) through (g) below. Figures NB-1132.2-1 through NB-1132.2-3 are provided as an aid in defining the boundary and construction requirements of this Subsection.
(a) Attachments cast or forged with the component and weld buildup on the component surface shall be considered part of the component.
(b) Attachments, welds, and fasteners having a pressureretaining function shall be considered part of the component.
(c) Except as provided in (d) and (e) below, the boundary between a pressure-retaining component and an attachment not having a pressure-retaining function shall be at the surface of the component.
(d) The first connecting weld of a nonpressure-retaining structural attachment to a component shall be considered part of the component unless the weld is more than 2t from the pressure-retaining portion of the component, where is the nominal thickness of the pressure-retaining material. Beyond 2t from the pressure-retaining portion of the component, the first weld shall be considered part of the attachment.
(e) The first connecting weld of a welded nonstructural attachment to a component shall be considered part of the attachment. At or within 2t from the pressure-retaining portion of the component, the first connecting weld shall conform to NB-4430.
(f) Mechanical fasteners used to connect a nonpressureretaining attachment to the component shall be considered part of the attachment.
(g) The boundary may be located further from the pressure- retaining portion of the component than as defined in (a) through (f) above when specified in the Design Specification.
ELECTRICAL AND MECHANICAL PENETRATION ASSEMBLIES
Electrical and mechanical penetration assemblies shall be constructed in accordance with the rules for vessels, except that the design and the material performing the electrical conducting and insulating functions need not meet the requirements of this Subsection.
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