applied fracture mechanics

332Applied Fracture Mechanicsdeveloped another computer code named PSQUIRT (probabilistic see page quantification ofupsets in reactor tubes) to determine the probability of leak age of piping made of stainlesssteel and carbon steel subjected to intergranular stress corrosion cracking (IGSCC) andcorrosion fatigue. Failure probabilities of a piping component subjected to SCC wascomputed in (Priya C et al., 2005 and Guedri et al., 2009a , 2009b) using a Monte Carlosimulation (MCS) technique.In this chapter, a piping component made of AISI 304 stainless steel is considered for theanalysis, because this type of steel is highly susceptible to SCC. Empirical relations are usedto model the initiation and early growth rate of cracks. Fracture mechanics concepts areused deterministically in this study. Although the general methodology recommended inthe computer program Piping Reliability Analysis Including Seismic Events (pc-PRAISE)(Harris et al., 1996) is used for the modeling of initiation and propagation of cracks, theAmerican Society of Materials (ASM) recommendations (American Society of Materials,1996) are used for computing the stress intensity factors. The microstructural properties ofthe material and operating conditions like pressure and temperature show variations duringthe lifetime of the pipe. In order to account for these variations, degree of sensitization,applied stress, initiation time of cracks, crack growth velocity after initiation, and initialcrack length are considered as random variables.The present calculations build on past studies by the nuclear power industry: GeneralElectric Company (GEC) (General Electric Company, 1982a, 1982b) and Nuclear RegulatoryCommission (NRC) (Hazelton , 1988), which have addressed both Inter-Granular Stress-Corrosion Cracking (IGSCC) causes and preventive actions. A critical issue has been thedifficulty of using Ultrasonic Testing (UT) to detect IGSCC. Pacific Northwest NationalLaboratory (PNNL) past research on Non-Destructive Examination (NDE) reliability hasincluded systematic studies to quantify NDE effectiveness. The first statistically based datafor the Probability of Detection (POD) of IGSCC in weld of stainless steel piping weregenerated based on a piping inspection round robin (Doctor et al., 1983). The resulting PODdata related to crack size and other important variables covered the performance of severalinspection teams participating in the round robin. The first part of this chapter describes thestress-corrosion cracking model used in the pc-PRAISE (Harris et al., 1981, 1986a, 1986b) forsimulating the initiation and growth of IGSCC cracks. This model is based on laboratorydata from IGSCC tests in combination with calibration of the model using field data frompipe-cracking experience. PNNL has improved on the prior calibrations (Harris et al., 1986b)by making adjustments to the modeling of plant loading/unloading cycles in addition toadjustments to residual stress levels. The crack detection data (POD curves) by use of the pc-PRAISE model are also described. A parametric approach was adopted in the presentcalculations to characterize IGSCC by a single damage parameter (Dsigma). This parameterdepends on residual stresses, environment conditions, and degree of sensitization. In thesecond part, a matrix of calculations to address an example of large pipe size, materials, andservice conditions was developed. The results of these calculations quantify the reductionsin failure probabilities that can be achieved with various In-Service Inspection (ISI)strategies. The final subpart of this chapter presents conclusions regarding ISI effectivenessas a mitigation action to enhance the reliability of Boiler Water Reactor piping.