13th International Conference on Fracture June 16–21, 2013, Beijing, China -10- due to Raju and Newman [27] and the ‘global’ collapse solution for the reference stress are best to estimate C* in the analysis for pipes. ‘Global’ solutions of reference stress are based on the collapse of the entire cross-section at the site of a defect. For a semi-elliptical axial defect in a pipe subjected to an internal pressure p, R6 [13] gives the reference stress as: i e e ref Pipe R R a batea c R a p , ln 1 (13) where bate(a, c) is given by : R a a c a bate a c e 2 1 1.61 ( , ) (14) where bate(a, c) function of dimensions, a is crack depth, c is half crack length at the surface and Ri and Re are the internal and external radii of the pipe, respectively. Figure 5 gives an example of comparison of crack growth analysis of the C(T) and pipes geometries in both parent and weld P22 steel tested at 565 oC. Fig. 6a shows little difference between parent and heat affected zone (HAZ) region tests for the C(T) P22 specimens. On the other hand Fig. 6b, for the pipe test whilst not showing a noticeable difference between parent and HAZ cracking it does show an effect due to geometry when compared with the databand of Fig. 6a. This could be due to constraint as well as the fact that derivation of data from pipe test are much more difficult than for standard C(T) specimen [8,28]. This highlights the fact that more tests would be needed to improve the validation of laboratory data with component data. a) b) Figure 4: a) Comparison of welded and parent crack growth rate for P22 steel tested at 565 oC, and b) Comparison of crack growth versus C* for P22 CT and pipe specimens with C(T) data band (Fig. 6a) showing the effects of geometry constraint on crack growth [3]. 2. CONCLUSIONS Creep and fatigue crack growth models as well as residual defect assessment codes need reliable 1.0E-06 1.0E-05 1.0E-04 1.0E-03 1.0E-02 1.0E-01 1.0E+00 1.0E-06 1.0E-05 1.0E-04 1.0E-03 1.0E-02 1.0E-01 C* [MPam/h] da/dtExp [mm/h] CT - PM CT - HAZ CT - Experimental data bound - PM & HAZ 1.0E-06 1.0E-05 1.0E-04 1.0E-03 1.0E-02 1.0E-01 1.0E+00 1.0E-07 1.0E-06 1.0E-05 1.0E-04 1.0E-03 1.0E-02 1.0E-01 C* [MPam/h] da/dt Exp [mm/h] CT - Experimental data bound - P22 - HAZ Mean fit to steady state CCG data - CT - HAZ Pipe P data - Estimated HAZ properties Initial CCG rate prediction line Pipe P data - PM properties
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