Document: NRC Regulatory Guide
Document ID: a4944d20-ef6e-480b-a45d-14425bedd2e5
Document Type: regulatory_guide
Title: ASME Code Cases Not Approved for Use (Rev. 8)
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML2219/ML22196A065.pdf
Revision Date: 2023-05
Chapter: 
Section ID: RG-1.193
CFR Part: 
CFR Title: 

Content:
are nonmandatory. Licensees intending to use Code Case N-806 must submit a plant-specific request to the NRC staff for review and approval before its implementation. N-813 Alternative Requirements for Preservice Volumetric and Surface Examination, Section XI, Division 1 Code Case N-813 is an alternative to the provisions of the 2010 Edition of the Section XI, Paragraph IWB-3112, which does not allow the acceptance of flaws detected in the preservice examination by analytical evaluation. Code Case N-813 would allow the acceptance of these flaws through analytical evaluation. Under Section XI, Paragraph IWB-3112, any preservice flaw that exceeds the acceptance standards of Table IWB-3410-1 must be removed. Although it is recognized that operating experience has shown that large through-wall flaws and leakages have developed in previously repaired welds as a result of weld residual stresses, the NRC has the following concerns in regard to the proposed alternative in Code Case N-813: (3) The requirements of Section XI, Paragraph IWB-3112, were developed to ensure that defective welds were not placed in service. A preservice flaw detected in a weld that exceeds the acceptance standards of Table IWB-3410-1 demonstrates poor workmanship or inadequate welding practice and procedures. The unacceptable preservice flaw needs to be removed, and the weld needs to be repaired before it is placed in service. (4) Under Code Case N-813, large flaws would be allowed to remain in service because Section XI, Paragraphs IWB-3132.3, through IWB-3643, allows a flaw up to 75% through-wall to remain in service. Larger flaws could grow to an unacceptable size between inspections, thus reducing structural margin and potentially challenging the structural integrity of safety-related Class 1 and Class 2 piping. Paragraph C-3112(a)(3) of Code Case N-813 provides the same alternatives for Class 2 piping as that of Paragraph B-3122(a)(3). The staff has the same concerns for Class 2 piping as it