Document: NUREG-0800
Document ID: d5452e7b-1e61-498b-9e3d-71073b3328ef
Document Type: srp
Title: LEAK-BEFORE-BREAK EVALUATION PROCEDURES
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0302/ML030280295.pdf
Revision Date: 2023-06
Chapter: 3
Section ID: 3.6.3
CFR Part: 
CFR Title: 

Content:
that currently preclude generic use of limit load analyses to evaluate leak-before-break conditions for eliminating pipe restraints. However, a modified limit-load analy sis can be used for austenitic steel piping to demonstrate accept able margins as indicated below: Construct a master curve where a stress index, SI, given by SI = S + M Pm (1) is plotted as a function of postulated total circumferential through wall flaw length, L, defined by L:28R (2) where S = 2 a- [ 2 sin• - sin e 1, (3) : 0.5 [(IT- 9) -IT ( P mIa)], (4) 0 = half angle in radians of the postulated throughwall circum ferential flaw, R = pipe mean radius, that is, the average between the inner and outer radius, Pm = the combined membrane stress, including pressure, deadweight, and seismic components, M = the margin associated with the load combination method (that is, absolute or algebraic sum) selected for the analysis, mf = flow stress for austenitic steel pipe material categories. If 0 + from Eqs. (2) and (4) is greater thanTt , then S = 2or [ sin• J, (5) TT where - TT (P m/0f). (6) 3.6.3-7 When the master curve is constructed using Eqs. (1), (2), and (3) or (5), the allowable circumferential throughwall flaw length can be determined by entering the master curve at a stress index (SI) value determined from the loads and austenitic steel piping material of interest. The allowable flaw size determined from the master curve at the appropriate SI value can then be used to determine if the required margins are met. Allowable values of 9 are those that result in S being greater than zero from Eqs. (3) and (5). The flow stress used to construct the master curve and the definition of SI used to enter the master curve are defined for each material category as follows: Base Metal and TIG Welds: The flow stress used to construct the master curve is (a = + () 05 y u when the yield strength, oy , and the ultimate strength, cru' at temperature are known. If the yield and ultimate strengths at temperature