Document: NUREG-0800
Document ID: 22c713a3-851c-4195-8d52-e7a90bcbeed0
Document Type: srp
Title: LEAK-BEFORE-BREAK EVALUATION PROCEDURES
Source: NUREG-0800
Source URL: https://www.nrc.gov/docs/ML0636/ML063600396.pdf
Revision Date: 2023-06
Chapter: 3
Section ID: 3.6.3
CFR Part: 
CFR Title: 

Content:
s that currently preclude generic use of limit load analyses to evaluate LBB conditions for eliminating pipe restraints. However, a modified limit-load analysis can be used for austenitic steel piping to demonstrate acceptable margins as indicated below. A master curve is constructed where a stress index (SI), is plotted as a function of postulated total circumferential throughwall flaw length, L. SI and L are expressed as m, SI = S + M P (1) L = 2 è R, (2) 3.6.3-10 Revision 1 - March 2007 where f S = 2 ó [ 2 sin â - sin è ] / ð, (3) m f â = 0.5 [ (ð - è) - ð ( P / ó ) ], (4) è = half angle in radians of the postulated throughwall circumferential flaw, R = pipe mean radius (the average of the inner and outer radii), m P = the combined membrane stress, including pressure, deadweight, and seismic components, M = the margin associated with the load combination method (absolute or algebraic sum) selected for the analysis, and f ó = flow stress for austenitic steel pipe material categories. If è + â from Equations (2) and (4) are greater than ð , then f S = 2 ó [ sin â ] / ð, (5) where m f â = - ð ( P / ó ), (6) When the master curve is constructed using Equations (1), (2), and (3) or (5), the allowable circumferential throughwall flaw length can be determined by entering the master curve at a 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 è are those that result in S being greater than zero from Equations (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. (vii) Base Metal and TIG Welds: The flow stress used to construct the master curve is expressed as f y u ó = 0.5 ( ó + ó ), y u when the yield strength, ó , and the