IGSCC cracking

Fig. 16 IGSCC crack growth rate versus corrosion potential (ECP) for sensitized Type 304 SS in high-temperature water as a function of solution conductivity (rc25) for given values for the degree of sensitization (15 C cm 2) and stress intensity (27.5 MPa.m1/ 2). The experimental data were measured for ambient temperature conductivities, K2S, ranging from 0.1 to 0.3 pS cm-1. The citations given in the figure are those presented in Ref. 43.

Extensive IGSCC cracking has been discovered in several BWR access hole covers. 

The U.S. NRC has also provided recommended IGSCC crack growth rates for use in dispositioning detected and sized flaws in piping (NUREG-0313, Revision 2 [7.5]). These data, in conjunction with geometry specific stress intensity solutions, can be used to determine any subsequent crack growth. This method does not consider the time to crack initiation it relies on inspection to detect cracks or on historical data to predict the time to initiation. 

Figure 87. Predicted accumulated damage for IGSCC (crack length) in a Boiling Water Reactor as a function of the reactor operating history over ten years and as a function of the water chemistry protocols employed. Reprinted from Ref. 9, Copyright (1995) with permission from Elsevier.

Cracks, Corrosion, Pitting, Wall thickness, IGSCC... 

Many instances of intergranular stress corrosion cracking (IGSCC) of stainless steel and nickel-based alloys have occurred in the reactor water systems of BWRs. IGSCC, first observed in the recirculation piping systems (21) and later in reactor vessel internal components, has been observed primarily in the weld heat-affected zone of Type 304 stainless steel. 

Intergranular stress-corrosion cracking (IG-SCC) can occur in some sensitized materials when placed under tensile stress. Thus DL-EPR has been used to study the effects of aging time on the susceptibility of Alloy 600 to IGSCC, as shown in Fig. 41 (39). This work also shows the need to modify the experimental parameters of the test to achieve optimal correlation for alloys other than Type 304SS, in this case lowering the KCNS concentration and the temperature while raising the peak potential and the scan rate. 

Fig. 13 Dependence of calculated crack growth rate on the electrochemical crack length for IGSCC in Type 304 SS in NaCl solution.

More recently, sophisticated SSRT (Slow Strain Rate Technique) equipment has been installed on some BWRs, in order to measure the tendency to IGSCC of some sensitized austenitic steels [6]. These methods have lately been also used for directly measuring crack propagation rate in TC samples [5]. 

As with all standardized tests (e g., the ASTM A 262 procedures previously discussed), correlations must be established between the EPR Pa values and service performance. For example, a criterion of Pa < 2 C/cm2 has been proposed for adequate resistance to intergranular corrosion leading to intergranular stress-corrosion cracking (IGSCC) of type 304 and 304L pipe and welds. Other limits would be set depending on the material, application, and environment (Ref 105, 106). 

X. liu, W. Zhang, G. S. Frankel, Effect of stress on penetration of IGC in Al alloys transition ofIGCto IGSCC in Chemistry and Electrochemistry of Stress Corrosion Cracking ... 

Fig. 9.25 Surface of IGSCC initiation showing the cold work layer and heavy oxides at the crack mouth [96].

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