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

2013 ◽  
Vol 135 (2) ◽  
Author(s):  
Zhanpeng Lu ◽  
Tetsuo Shoji ◽  
He Xue ◽  
Chaoyang Fu
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Thermal Activation ◽  
Alloy 600 ◽  
Pressurized Water Reactor ◽  
Pressurized Water ◽  
Weld Metals ◽  
Primary Water ◽  
Nickel Base

The fundamental correlations such as crack growth rate (CGR) versus K for primary water stress corrosion cracking (PWSCC) of nickel-base alloys in simulated pressurized water reactor environments are quantified with the theoretical model based on the combination 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 by Section XI Nonmandatory Appendix O of the ASME Boiler and Pressure Code for flaw evaluation. MRP also proposed a CGR disposition curve in a report MRP 115 for PWSCC of Alloy 82/182/132 weld metals. Stress intensity factor (K), temperature and thermal activation energy are included in both MRP 55 and MRP 115 reports. Both MRP 55 and MRP 115 are engineering-based. The results of mechanism-based modeling are compared with the screened experimental data for typical PWSCC systems of nickel-base alloys and the consistence is observed.

Mechanistic Formulation of PWSCC Growth Rates of Ni-Base Alloys and Weld Metals

2011 ◽  
Author(s):  
Zhanpeng Lu ◽  
Tetsuo Shoji ◽  
He Xue ◽  
Chaoyang Fu
Keyword(s):  
Thermal Activation ◽  
Structural Integrity ◽  
Thermal Activation Energy ◽  
Evaluation Procedure ◽  
Alloy 600 ◽  
Pressurized Water Reactor ◽  
Pressurized Water ◽  
Weld Metals ◽  
Primary Water ◽  
Integrity Analysis

Several Ni-base alloys and their weld metals such as Alloy 600 and Alloy 82/182 suffered from stress corrosion cracking in pressurized water reactor primary water environments. 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 by Section XI Nonmandatory Appendix O of the ASME Boiler and Pressure Code for flaw evaluation. MRP also proposed a CGR disposition curve in MRP report 115 for PWSCC of Alloy 82/182/132 weld metals. In the same fashion, JSME and JNES also provided CGR disposition curves in the flaw evaluation procedure in structural integrity analysis. Stress intensity factor (K), temperature and thermal activation energy are included in both MRP 55 and MRP 115 reports. Both MRP 55 and MRP 115 are engineering-based rather than mechanism-based. The fundamental correlations such as crack growth rate vs. K are quantified based on the theoretical model and screened experimental data, which are compared to the reported disposition curves and used for improving the prediction.

Examinations of Oxidation and Sulfidation of Grain Boundaries in Alloy 600 Exposed to Simulated Pressurized Water Reactor Primary Water

2013 ◽  
Vol 19 (3) ◽  
pp. 676-687 ◽  
Author(s):  
D.K. Schreiber ◽  
M.J. Olszta ◽  
D.W. Saxey ◽  
K. Kruska ◽  
K.L. Moore ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Atom Probe Tomography ◽  
Atom Probe ◽  
Alloy 600 ◽  
Pressurized Water Reactor ◽  
Intergranular Attack ◽  
Pressurized Water ◽  
Primary Water

AbstractHigh-resolution characterizations of intergranular attack in alloy 600 (Ni-17Cr-9Fe) exposed to 325°C simulated pressurized water reactor primary water have been conducted using a combination of scanning electron microscopy, NanoSIMS, analytical transmission electron microscopy, and atom probe tomography. The intergranular attack exhibited a two-stage microstructure that consisted of continuous corrosion/oxidation to a depth of ~200 nm from the surface followed by discrete Cr-rich sulfides to a further depth of ~500 nm. The continuous oxidation region contained primarily nanocrystalline MO-structure oxide particles and ended at Ni-rich, Cr-depleted grain boundaries with spaced CrS precipitates. Three-dimensional characterization of the sulfidized region using site-specific atom probe tomography revealed extraordinary grain boundary composition changes, including total depletion of Cr across a several nm wide dealloyed zone as a result of grain boundary migration.

Propose of Simplified Stress Intensity Factor Equation for SCC Extension of the Pipe Welds

2008 ◽  
Author(s):  
Mayumi Ochi ◽  
Kiminobu Hojo ◽  
Itaru Muroya ◽  
Kazuo Ogawa
Keyword(s):  
Stress Intensity Factor ◽  
Stress Intensity ◽  
Intensity Factor ◽  
Stress Intensity Factors ◽  
Crack Extension ◽  
Crack Depth ◽  
Alloy 600 ◽  
Intensity Factors ◽  
Axial Crack ◽  
Extension Analysis

Alloy 600 weld joints have potential for primary water stress corrosion cracks (PWSCC). At the present time it has been understood that PWSCC generates and propagates in the Alloy 600 base metal and the Alloy 600 weld metal and there has been no observation of cracking the stainless and the low alloy steel. For the life time evaluation of the pipes or components the crack extension analysis is required. To perform the axial crack extension analysis the stress intensity database or estimation equation corresponding to the extension crack shape is needed. From the PWSCC extension nature mentioned above, stress intensity factors of the conventional handbooks are not suitable because most of them assume a semi-elliptical crack and the maximum aspect ratio crack depth/crack half length is one (The evaluation in this paper had been performed before API 579-1/ASME FFS was published). Normally, with the advance of crack extension in the thickness direction at the weld joint, the crack aspect ratio exceeds one and the K-value of the conventional handbook can not be applied. Even if those equations are applied, the result would be overestimated. In this paper, considering characteristics of PWSCC’s extension behavior in the welding material, the axial crack was modeled in the FE model as a rectangular shape and the stress intensity factors at the deepest point were calculated with change of crack depth. From the database of the stress intensity factors, the simplified equation of stress intensity factor with parameter of radius/thickness and thickness/weld width was proposed.

Advanced Inlay System for Inlet/Outlet Nozzles of RV for Preventive Maintenance Against Alloy 600 PWSCC in Japanese PWR Plants

2013 ◽  
Author(s):  
Kazuhide Yamamoto ◽  
Masahiko Kizawa ◽  
Hiroki Kawazoe ◽  
Yuki Kobayashi ◽  
Ken Onishi ◽  
...  
Keyword(s):  
Preventive Maintenance ◽  
Heat Treatments ◽  
Residual Tensile Stress ◽  
Alloy 600 ◽  
Pressurized Water Reactor ◽  
Pressurized Water ◽  
Loss Of Coolant Accident ◽  
Nuclear Plants ◽  
Alloy 690 ◽  
Primary Water

Because many nuclear plants have been in operation for ages, the importance of preventive maintenance technologies is getting higher. One conspicuous problem found in pressurized water reactor (PWR) plants is the primary water stress corrosion cracking (PWSCC) observed in Alloy 600 (a kind of high nickel based alloy) parts. Alloy 600 was used for butt welds between low alloy steel and stainless steel of nozzles of Reactor Vessel (RV), Steam Generator (SG), and Pressurizer (Pz). As PWSCC occurred at these parts may cause Loss of Coolant Accident (LOCA), preventive maintenance is necessary. PWSCC is considered to be caused by a mixture of three elements: high residual tensile stress on surface, material (Alloy 600) and environment. PWSCC can be prevented by improving one of the elements. MHI has been developing stress improvement methods, for example, Water Jet Peening (WJP), Shot Peening by Ultrasonic vibration (USP), and Laser Stress Improvement Process (L-SIP). According to the situation, appropriate method is applied for each part. WJP has been applied for RV nozzles of a lot of plants in Japan. However PWSCC was observed in RV nozzles during the inspection before WJP in recent years, MHI developed the Advanced INLAY system to improve the material from Alloy 600 to Alloy 690. Alloy 600 on the inner surface of the nozzles is removed and welding with Alloy 690 is performed. In addition, heat treatments for the nozzles are difficult for its structural situation, so ambient temperature temper bead welding technique for RV nozzles was developed to make the heat treatments unnecessary. This paper describes the specifications of the advanced INLAY system and introduces the maintenance activities which MHI has applied for three plants in Japan by March 2012.

Kinetic Study of the Low Temperature Internal Oxidation of Nickel Based Model Alloys Exposed to PWR Primary Water

2008 ◽  
Vol 595-598 ◽  
pp. 449-462 ◽  
Author(s):  
Benoît Ter-Ovanessian ◽  
Julien Deleume ◽  
Jean Marc Cloué ◽  
Eric Andrieu
Keyword(s):  
Ternary Alloys ◽  
Pressurized Water Reactor ◽  
Oxide Interface ◽  
Intergranular Stress Corrosion ◽  
Pressurized Water ◽  
Free Oxygen ◽  
Primary Water ◽  
Nickel Base ◽  
The One ◽  
Intergranular Stress Corrosion Cracking

Two Ni-Fe-Cr ternary alloys have been oxidized in simulated pressurized water reactor primary water at 360°C for 1000 h. The chemical composition of those alloys were chosen in order to be representative of the one of chromium depleted areas under the oxide scale of industrial alloys (e.g. alloy 600) exposed in the same conditions. The resulting oxidized structures (corrosion scale and underlying metal) were characterized using complementary analytical methods (FEG-SEM, TEM, SIMS, optical microscopy). On the one hand, the characterized external oxide layer is very close to the one observed on industrial nickel-base alloys, hence validating the use of such model alloys. On the other hand, both free oxygen and oxides have been detected at grain boundaries several micrometers under the metal/oxide interface. Implications of such a finding on the involved transport mechanisms for oxygen and the intergranular stress corrosion cracking resistance of nickel-base alloys are then discussed.

Do All RPV Head Penetration Leaks Have the Potential to Cause Head Wastage?

2004 ◽  
Author(s):  
Chandra M. Roy ◽  
John R. Fessler ◽  
Jude R. Foulds ◽  
Ronald M. Latanision ◽  
David E. Taylor
Keyword(s):  
Water Stress ◽  
Pressure Vessel ◽  
Recent Experience ◽  
Alloy 600 ◽  
Pressurized Water Reactor ◽  
Pressurized Water ◽  
Head Penetration ◽  
Failure Risk ◽  
Primary Water ◽  
Reactor Pressure

The identification of the PWSCC (Primary Water Stress Corrosion Cracking) mechanism responsible for leakage from an Alloy 600 nozzle tube of a PWR RPV (pressurized water reactor reactor pressure vessel) head more than a decade ago led to a significant body of research into understanding the phenomenon and to development of bases for safely managing primary pressure boundary integrity. However, the relatively recent experience at Davis-Besse, wherein penetration leakage resulted in significant vessel head material wastage, led to the heretofore unconsidered issue of vessel failure risk due to head rupture. This paper addresses, in preliminary fashion, one key input to determining the risk associated with head material wastage and potential rupture — the local environmental and fluid conditions associated with a range of leak paths. The results indicate a need for rigorous prediction of fluid conditions for a range of leak situations to help establish criteria for addressing penetration leaks.

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