Document: NRC Regulatory Guide
Document ID: 1d715751-9321-4481-a46f-4ff802a5efe0
Document Type: regulatory_guide
Title: Service Limits and Loading Combinations for Class 1 Linear-Type Supports + HISTORY – HISTORY 10/2006 – DG-1168 , Proposed Revision 2
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML0630/ML063000449.pdf
Revision Date: 2023-06
Chapter: 
Section ID: RG-1.124
CFR Part: 
CFR Title: 

Content:
including ASME Code Cases N-71 and N-249. Code cases identified as “Conditionally Acceptable Section III Code Cases” are acceptable, provided that they are used with the identified limitations or modifications. DG-1168, Page 3 Design by Linear-Elastic Analysis a. Sy and Su at Temperature Tables U and Y-1 in Subpart 1 of Part D of Section II and Tables 3, 4, and 5 in the latest accepted versions2 of ASME Code Cases N-71 and N-249 give the relevant material properties when the linear-elastic-analysis method is used to design Class 1 linear-type component supports. These tables list values at various temperatures for the minimum yield strength Sy and ultimate tensile strength Su. At room temperature, Sy varies from 62 percent to 93 percent of Su for component support materials. Levels of service limits that are derived from either material property alone might be insufficient to provide a consistent safety margin. Section III recognizes this issue in NF-3322.1(a), which defines the allowable stress in tension on a net section as the lesser of two values, 0.6Sy or 0.5Su. Although NF-3322.1(a) specifies allowable tensile stress in terms of both Sy and Su, the rest of NF-3320 notes other allowable service limits in terms of Sy only. This does not maintain a consistent design margin for those service limits related only to material properties. Modifications similar to NF-3322.1(a) should be employed for all those service limits. b. Allowable Increase of Service Limits Although NF-3321.1(a) and F-1334 of Section III of the ASME Code permit the increase of allowable stresses under various loading conditions, NF-3321.1(b) limits the increase to less than or equal to two-thirds of the critical buckling stress for compression and compression flange members. NF-3322.1(c) of Section III derives critical buckling stresses with normal design margins. Because buckling prevents “shakedown” in the load-bearing member, NF-3322.1(c) should be controlling. Also, buckling is the