ASME BPVC-III NB ADD-2008 pdf free download.Division 1 – Subsection NB Class 1 Components.
(a) Fxcept a. pennitted in (N below. the portions of appurtenances having a pressure retaining functim shall he designed in accordance with the rules for components.
(b) Small diamcier a purten4sncc fabrication weld joints may he designed using weld joint details in accordance with Fig. NB-4440-l. provided the following requirements arc mci.
(1) The appunenance weld joint shall have an outside diameter equal to PS 2 ibN 50i or less (sec Fig. NH4440 -I).
(2) The design of the welded joints shall he such that
the stresses will not exceed the limits described in NH-
3220 and tabulated in Section II. Part I). Subpart I. Tables
2A and 2B.
(3) A fatigue strength reduction factor of 4 shall be used in the fatigue analysis of the joints.
(4) The requirementv of NB-44.40 and NB.52t1i0 shall be satisfied.
NB-3 137 ReinrOrcemeni for Openings
The requirements applicable to vessels and piping are contained in NB-333() and NB-3643. respectively.
NB-3200 DESIGN BY ANALYSIS NH-32l0 IWSIGN CRlTKRl
NB-32l I Requirements for Acceptability
The requiremesns for the acceptability of a design by analysis are given in (a) through (d) below.
(a) mc design shall be such that stress intensities will not exceed the limits described in this Subarticle and in NB-3 100 and tabulated in Section II. Part D. Subpart I. Tables 2A, 2B. and 4.
(b) The design details shall conform to the rules given in NH-3100 and those given in the Subartick applicable to the specific component.
(c) For configurations where compressive stresses occur, in addition to the requirements in (a) and tb) above. the critical buckling stress shall be taken into account. For the special case of external pressure. NB-3 133 applies.
fd) Protection against nonductilc fracture shall be pro- sided by satisfying one of the following provisions:
(1) performing an evaluation of service and test conditions by methods similar to those contained in Appendix or
(2) for piping, pump, and valve material thickness greater than 2h12 in. (64 min establishing a lowest service
Basis for Determining Stresses
The theory of failure, used in the rules of this Subsection for combining stresses, is the maximum shear stress theory.
The maximum shear stress at a point is equal to one half the difference between the algebrically largest and the algebraically smallest of the three principal stresses at the point.
Terms Relating to Stress Analysis
Terms used in this Subection relating to stress analysis are defined in the follow ing subparagraphs.
NB-3213.1 Stress Intensity. Stress intensity is defined as twice the maximum shear stress, which is the difference between the algebraically largest principal stress and the algebraically smallest principal stress at a given point.
Tensile stresses are considered positive and compressive stresses are considered negative.
NB-3213.2 Gross Struetural Discontinuity. Gross structural discontinuity is a geometrice or material discontinuity which afects the stress or strain distribution through the entire wall thickness of the pressure retaining member.
Gross discontinuity type stresses are those portions of the actual stress distributions that produce net bending and membrane force resultants when integrated through the wall thickness. Examples of gross structural discontinuities are head-to-shell and flange -to- shell junctions, nozzles (NB-3331), and junctions between shells of different diameters or thicknesses.
NB-3213.3 Local Structural Discontinuity. Local structural discontinuity is a geometrie or material discontimuity which affects the stress or strain distribution through a fractional part of the wall thickness. The stress distribution associaed with a local discontinuity causes only very localized types of deformation or stain and has no significant effeet on the shell type discontinuity deformations. Examples are small flletl radi, small attachments, and partial