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:
the same as the Fen expression recently developed by the NRC, but the equations for the transformed environmental parameters are different, and the Fen equation may yield nonconservative values of Fen in cases that use the average temperature (see item (f)). f. -2420 Determination of Transformed Temperature: (1) -2421 of the Code Case states that the transformed temperature is based on “the average of the highest and lowest metal temperatures of the surface in contact with the fluid in the transients constituting the stress cycle.” The NRC disagrees with this approach because it is not consistent with the Fen methodology and because it can be nonconservative. i. To be consistent with the Fen methodology, an average temperature for the transient should consider the DG-1408, Page 10 CODE CASE NUMBER TABLE 1 UNACCEPTABLE SECTION III CODE CASES SUMMARY DATE OR SUPPLEMENT/ EDITION threshold temperature to estimate Fen during a load cycle, which may be significantly higher than the minimum temperature of the transient. ii. Limited NRC calculations indicate that using either an average transient temperature or an average of the transient maximum temperature and the Fen threshold temperature does not always yield a conservative Fen estimate when compared to the results obtained from an integrated Fen using the modified rate approach. (2) -2422 defines the transformed temperature for carbon and low-alloy steels for temperatures up to 350 °C (660 °F). The NRC’s updated research only includes data up to 325 °C (615 °F); therefore, the updated Fen expression for carbon and low-alloy steels is only applicable for temperatures up to 325 °C. (3) -2423 defines the transformed temperature for wrought and cast austenitic stainless steels for temperatures above 325 °C (615 °F) as constant (T* = 1). The NRC’s updated research only includes data up to 325 °C (615 °F), and the updated Fen expression for wrought and cast austenitic stainless steels does not plateau at