Recent studies have shown that a subcritical surface crack, due to primary water stress corrosion cracking (PWSCC), can transition to a through-wall crack (TWC) with significant differences between the inner diameter (ID) and outer diameter (OD) crack lengths. This behavior has been observed for both circumferential and axial cracks. Recently, a surface to TWC transition model has been developed for circumferential cracks using existing K and COD (crack opening displacement) solutions for nonidealized circumferential TWCs. In this paper, a similar crack transition model (CTM) was developed for axial cracks. As a first step, a study was conducted to define the appropriate crack front shape for nonidealized axial TWCs. Then, elastic finite element analyses were carried out to develop K and COD solutions using these crack front shapes. The newly developed solutions were utilized for the CTM. The present CTM includes a criterion for transitioning the final surface crack to the initial nonidealized TWC. This criterion determines when the transition should occur (based on surface crack depth) and determines the two crack lengths (at ID and OD surfaces) of the initial nonidealized TWC. Furthermore, nonidealized TWC growth calculation can be conducted using the proposed model. Example results (crack length and COD) obtained from the proposed model were compared to those obtained from the natural crack growth simulations. Results presented in this paper demonstrated the applicability of the proposed model for simulating axial crack transition.