Zhanpeng Lu

Effects of Loading Mode and Temperature on Stress Corrosion Crack Growth Rates of a Cold-Worked Type 316L Stainless Steel in Oxygenated Pure Water

Abstract The stress corrosion cracking (SCC) growth rates of a cold-worked Type 316L (UNS S31603) stainless steel specimen in high-purity water at various temperatures were measured under various l...

Unified Interpretation of Crack Growth Rates of Ni-base Alloys in LWR Environments

Primary water stress corrosion cracking (PWSCC) of vessel penetrations (VP) fabricated from nickel based alloys such as alloy 600 and alloy 182 weld metal has created a great demand for elucidation of the cracking mechanism and for development of life prediction technologies. The generalized FRI crack growth rate (CGR) formulation was proposed, based on a deformation/oxidation mechanism and a theoretical crack tip strain rate equation derived by the authors. The effects of crack tip oxidation and crack tip mechanics and of their interactions on crack growth can be quantified. Experimental and actual plant data of CGR for alloy 600 in PWR primary water, which are sometimes scattered in CGR-K diagrams, are interpreted with the generalized CGR formulation, emphasizing the effects of temperature, K, yield strength and variations of K with time. It is suggested that it is essential to determine the type of dependency of CGR on K for accurate flaw disposition. The generalized formulation provides a unique parameter for interpreting CGRs as well as a unified method for predicting CGRs within a narrow scattered band even under various testing parameters, which is the basis for accurately predicting component life.

Deterministic Formulation of the Effect of Stress Intensity Factor on PWSCC of Ni-Base Alloys and Weld Metals

The fundamental correlations such as crack growth rate (CGR) versus K for primarywater stress corrosion cracking (PWSCC) of nickel-base alloys in simulated pressurizedwater reactor environments are quantified with the theoretical model based on the combi-nation of crack tip mechanics and oxidation kinetics. Materials reliability program(MRP) proposed a CGR disposition curve in a report MRP 55 for PWSCC of thick-section Alloy 600 materials. This deterministic CGR equation has been adopted bySection XI Nonmandatory Appendix O of the ASME Boiler and Pressure Code for flawevaluation. MRP also proposed a CGR disposition curve in a report MRP 115 forPWSCC of Alloy 82/182/132 weld metals. Stress intensity factor (K), temperature andthermal activation energy are included in both MRP 55 and MRP 115 reports. Both MRP55 and MRP 115 are engineering-based. The results of mechanism-based modeling arecompared with the screened experimental data for typical PWSCC systems of nickel-basealloys and the consistence is observed. [DOI: 10.1115/1.4007471]Keywords: nickel base alloys, stress corrosion cracking, crack growth rate, high temper-ature water, pressurized water reactor, theoretical modeling

Factors affecting stress corrosion cracking (SCC) and fundamental mechanistic understanding of stainless steels

Abstract: The effects of metallurgical/material, environmental and mechanical factors and their synergistic contributions to stress corrosion cracking are summarized and analyzed. The contents are focused on stress corrosion cracking of materials in nuclear power plants and related key engineering parameters.

Effects of water chemistry on stress corrosion cracking of 316NG weld metals in high temperature water

Abstract Effects of dissolved oxygen concentration from 0·2 to 11 ppm on stress corrosion cracking growth rates of 316NG weld metals in pure water at 288°C were investigated. Crack growth rates in the weld metal with a ferrite content of about 6·5 wt-% are higher than those in the weld metal with a ferrite content of about 8·5 wt-% under the same test environments, which increased with increasing dissolved oxygen concentration from 0·2 to 2 ppm. The dependence of crack growth rates on dissolved oxygen concentration in the range from 2 to 11 ppm was affected by the ferrite content in the weld metals.

Crack Branching and Its Effect on Environmentally Assisted Cracking in High Temperature Water Environments

Crack kinking or branching has been observed in laboratory stress corrosion cracking tests and in some components suffering from stress corrosion cracking in nuclear power plant coolants. There are several types of crack branching: i.e., macroscopic multiple branching cracks, local crack branching or the combination of both. Crack branching affects the crack tip stress/strain distribution in terms of stress intensity factor and crack tip strain rate, and consequently affects crack growth behavior. The crack tip mechanical fields in some typical crack branching systems are quantified using empirical, analytical and numerical simulation methods. The effect of crack branching is less significant in contoured double cantilever beam specimens than in compact tension specimens for the same size and configuration of branched cracks. The applications of the analysis results to some observed crack branching phenomena of austenitic alloys in high temperature water environments are discussed based on the theoretical crack growth rate formulation.Copyright

Modeling Stress Corrosion Cracking Growth Rates Based Upon the Effect of Stress/Strain on Crack Tip Interface Degradation and Oxidation Reaction Kinetics

Quantitative prediction of environmentally assisted cracking such as stress corrosion cracking is one of the greatest concerns in lifetime management and consequent lifetime extension of light water reactors. Continuum mechanics has been applied to quantify the effect of crack tip mechanics on crack tip film degradation and its physical interaction with the oxidation kinetics. Besides such an effect, it has been realized that crack tip stress/strain can significantly affect the oxidation kinetics by a physical-chemical mode. The present paper focuses on optimizing crack tip asymptotic fields, oxidation kinetics laws, and their interaction modes for modeling stress corrosion cracking growth rates. Meanwhile, the physical-chemical effect of stress/strain on solid state oxidation kinetics at the stress corrosion crack tip is emphasized. The criteria for formulating stress corrosion cracking and optimizing input parameters are also discussed.Copyright

Deterministic Prediction of Stress Corrosion Crack Growth Rates in High Temperature Water by Combination of Interface Oxidation Kinetics and Crack Tip Asymptotic Field

Proper disposition of the environmentally assisted crack growth rate in terms of key engineering parameters is crucial for safe and economic long term operation of light water reactors. Accurately predicting stress corrosion crack growth rate requires the quantification of crack tip mechanics, crack tip oxidation kinetics and their interactions. Crack tip strain rate has been categorized as a fundamental parameter for stress corrosion cracking of austenitic alloys in light water reactor environments. Continuum mechanics is applied to quantify crack tip strain rate based on the crack tip asymptotic field. A general oxidation kinetics formulation is proposed based on solid state mass transport theory. Stress corrosion crack growth rates of austenitic alloys in high temperature water environments are formulated as a function of various engineering parameters by combination of interface oxidation kinetics and the crack tip asymptotic field. Recent experimental results of stress corrosion crack growth rates in simulated boiling water reactor and pressurized water reactor environments are analyzed and reflected in the model development and application. The importance of surface integrity on plant safety is emphasized. The plant material aging management methodology is applied to the recent cracking issues in light water reactors.© 2008 ASME

Understanding the Threshold Conditions for Stress Corrosion Cracking in Light Water Reactor Environments Based on the Deformation/Oxidation Mechanism

Stress corrosion cracking of structural materials is an important issue in light water reactors such as pressurized water reactors (PWR) and boiling water reactors (BWR). Proper disposition of the crack growth rate in terms of the engineering parameters is crucial for safe and economic long term operation. Threshold values of the stress intensity factor (K) have been used in some crack growth rate disposition guidelines such as JSME S NA1-2004 for austenitic stainless steels in BWR environments and flaw evaluation methodologies such as ASME XI Nonmandatory Appendix O-3230 for nickel-based Alloy 600 in PWR primary water environments. These threshold K values are based on the presently available experimental data that have been obtained mostly at relatively high K values. The threshold conditions for stress corrosion cracking in high temperature water are discussed more broadly for different cracking systems with various key-controlling parameters. The deformation/oxidation mechanism, which has been applied to quantification of the crack growth rate, is used here for analyzing the threshold conditions for stress corrosion cracking resulting from the interaction between the material and the environment under loading conditions.Copyright

Modeling and Quantitative Prediction of Environmentally Assisted Cracking Based Upon a Deformation-Oxidation Mechanism

In order to provide a quantitative tool for predicting EAC growth rates for austenitic alloys such as austenitic stainless steels, Alloys 600 and 182 in simulated LWR environments, a model based upon the synergistic effects of deformation and oxidation at the crack tip has been proposed. In this paper, the effects of hardening, variation of K with crack growth and oxidation kinetics on EAC growth rate are described with special emphasis on field applications. The results imply recent cracking incidences in BWR core shroud and Primary Loop Recirculation (PLR) piping and PWR Vessel Penetrations (VP). In particular, the significance of oxide analysis at the crack tip and also of a kinetic approach to oxidation under stress or strain condition is described. Potential future directions for mitigation of such cracking are discussed.Copyright