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:
comparable to that taken for Code Class 1 piping should be applied to define design basis break locations for ASME Code Class 2 and 3 piping of fluid systems in which piping breaks may be postulated. The piping design rules for Code Class 2 and 3 piping differ from those applicable to Code Class I piping as reflected by the stress limit of 0.8 (Sh + SA) provided for the determination of intermediate break locations. The stress limit of 0.8 (Sh + SA) is derived on a basis that is comparable to the stress limit specified for ASME Code Class 1 piping. The limit on stress for locating intermediate breaks in Code Class 2 and 3 piping runs or branch runs is not supplemented by a fatigue limit because the applicable codes (i.e., NC-3600 and ND-3600 of Section III of the ASME Code and the American National Standard Code for Pressure Piping, ANSI B31.1.0-1967) do not require analyses for cyclic loadings (other than that implied in the allowable values of expansion stress range, SA). However, if such analyses are performed, the limit on the cumulative usage factor provided for Code Class 1 piping should be applied in conjunction with the stress limitation for Code Class 2 and 3 piping. Pipe Sizes Subject to Breaks The pipe sizes to which this guide applies and the orientation of the postulated breaks with respect to the pipe axes are based upon (1) current piping fabrication techniques and (2) the results of stress analysis of applicable piping systems. Consideration of these factors indicate that circumferential breaks should be postulated for all piping runs and branch runs above the practical minimum of one-inch nominal pipe size. With regard to postulation of longitudinal breaks, a significant factor to be considered is that a majority of small ASME Code Class pipe lines (defined herein as less than four inches nominal pipe size) are of seamless construction (i.e., with no longitudinal weld seam and associated stress index). As expected from the type of fabrication and