High Temperature Flaw Evaluation Code Case N-934: Effect of Transients

Abstract The Working Group on High Temperature Flaw Evaluation (HTFE), which originally reported to both Section XI and Section III Division 5 but now is being assigned to Section XI Division 1, has developed a code case to address high temperature flaw evaluation (Code Case N-934). The code case integrates the creep rupture rules and material response of Section III Division 5 and the fracture rules in Section XI which are enhanced to address high temperature crack growth. The purpose of this procedure is to evaluate the growth of a single, characterized flaw for a defined evaluation period in a metallic component where the future thermomechanical loads are known or approximated. The procedure was originally developed to assess the growth of the flaw under periods of constant primary load assuming steady state creep. Code Case N-934 is currently being improved to include transient and secondary (thermal type loads) and will eventually address creep-fatigue crack growth also. Crack growth is accumulated over a series of time increments and creep rupture and crack instability are assessed. The method follows the guidance of the R5 code. Paper PVP2022-85957 [1] provided examples of use of the Code Case to provide HTFE assessments of several primary loaded crack growth problems under steady state conditions. In this paper, several examples of the use of the code case to assess HTFE transients based on the developing enhancements of Code Case N-934 are provided. The enhanced Code Case N-934 procedures are used to estimate the transient effects of creep crack growth and include the estimates of the C(t) integral for HTFE crack growth assessment. Comparisons of the estimates of C(t) with finite element solutions show that the Code Case procedures provide conservative estimates.