Document: NRC Regulatory Guide
Document ID: 7da9830f-b2a1-484a-82ce-5b0a588c4fce
Document Type: regulatory_guide
Title: Protection Against Pipe Whip Inside Containment
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML1229/ML12298A123.pdf
Revision Date: 2023-06
Chapter: 
Section ID: RG-1.46
CFR Part: 
CFR Title: 

Content:
experience. 5. Materials and Plant Protection 10. General calculated primary plus secondary stress intensities of 2/ Sm for ferritic steel and 2.4 Sm for austenitic steel. For stress intensity values calculated on an elastic basis that are 2 Sm or below in ferritic and 2.4 Sm or below in austenitic piping materials, the resulting strains in both materials are well within the 0.2% offset strain specified as the minimum yield strength by the applicable material specifications. Consequently, such piping locations are expected to behave elastically under the specified plant conditions. The 2 Sm or 2.4 Sm limit also is within the 3 Sm design limit specified in Section III for elastic-plastic fatigue exemption. When peak stress intensities in piping are evaluated, the allowable number of stress cycles determined by Section III of the ASME Code is lower than the stress cycles allowed for the primary plus secondary stress intensity limit. Therefore, the cumulative usage factor (U) is limited to a value of 0.1 to provide a margin on allowable cycles for peak stress intensities that is equivalent to the margin on allowable cycles derived solely from the primary plus secondary stress intensity limit. The cumulative usage factor limitation also accounts for fatigue strength reduction effects where unanticipated service conditions or unexpected and excessive nonlinear thermal gradients may develop in piping components. The limits on stress intensity and cumulative usage factor selected to determine piping break locations are based on the assumption that, despite the accepted conservatism in the ASME Code piping design rules, the system piping may suffer structural degradation of an unanticipated nature in service or may have its design margins unknowingly reduced by faulty design, improperly controlled fabrication, installation errors, or unexpected modes of operation. Therefore; the above limits provide additional margin over significant design basis.stress cycles (for a