Microstructure and Microchemistry of Inconel 600 STEAM Generator Tubing

2000 ◽  
Vol 6 (S2) ◽  
pp. 356-357
Author(s):  
V. Perovic ◽  
A. Perovic ◽  
G.C. Weatherly ◽  
A.M. Brennenstuhl
Keyword(s):  
Grain Boundary ◽  
Stress Corrosion ◽  
Stress Corrosion Cracking ◽  
Analytical Electron Microscopy ◽  
Corrosion Cracking ◽  
Steam Generators ◽  
Intergranular Stress Corrosion ◽  
Candu Reactors ◽  
Inconel 600 ◽  
Water Reactors

Inconel 600 is an austenitic Ni-Cr-Fe alloy which is extensively used for tubing in steam generators of pressurized light water reactors (PWR) and CANDU heavy water reactors, because of its excellent mechanical properties and corrosion resistance. However, there have been instances of intergranular stress corrosion cracking of tubes in operating steam generators. The chemistry and the structure of grain boundaries and grain boundary precipitation have emerged as factors of prime importance in understanding stress corrosion cracking and intergranular attack of nickel-base alloys (see e.g. ref. l).In this study analytical electron microscopy was used to determine the microstructure of grain boundary and matrix precipitates, grain boundary chromium content and dislocation substructure of selected steam generating tubes of CANDU reactors. The results of the in-service materials are compared with as-received material. Two JEOL 2010 STEM instruments were used in this study.

Effects of Weld Overlays on Leak-Before-Break Margins

2011 ◽  
Author(s):  
G. Angah Miessi ◽  
Peter C. Riccardella ◽  
Peihua Jing
Keyword(s):  
Stress Corrosion ◽  
Stress Corrosion Cracking ◽  
Corrosion Cracking ◽  
Operating Conditions ◽  
Intergranular Stress Corrosion ◽  
Pressurized Water ◽  
Weld Overlay ◽  
Water Reactors ◽  
Weld Overlays ◽  
Leak Before Break

Weld overlays have been used to remedy intergranular stress corrosion cracking (IGSCC) in boiling water reactors (BWRs) since the 1980s. Overlays have also been applied in the last few years in pressurized water reactors (PWRs) where primary water stress corrosion cracking (PWSCC) has developed. The weld overlay provides a structural reinforcement with SCC resistant material and favorable residual stresses at the ID of the overlaid component. Leak-before-break (LBB) had been applied to several piping systems in PWRs prior to recognizing the PWSCC susceptibility of Alloy 82/182 welds. The application of the weld overlay changes the geometric configuration of the component and as such, the original LBB evaluation is updated to reflect the new configuration at the susceptible weld. This paper describes a generic leak-before-break (LBB) analysis program which demonstrates that the application of weld overlays always improves LBB margins, relative to un-overlaid, PWSCC susceptible welds when all the other parameters or variables of the analyses (loads, geometry, operating conditions, analysis method, etc…) are kept equal. Analyses are performed using LBB methodology previously approved by the US NRC for weld overlaid components. The analyses are performed for a range of nozzle sizes (from 6″ to 34″) spanning the nominal pipe sizes to which LBB has been commonly applied, using associated representative loads and operating conditions. The analyses are performed for both overlaid and un-overlaid configurations of the same nozzles, and using both fatigue and PWSCC crack morphologies in the leakage rate calculations and the LBB margins are compared to show the benefit of the weld overlays.

Intergranular microchemistry and stress corrosion cracking

1981 ◽  
Vol 377 (1771) ◽  
pp. 477-501 ◽  
Keyword(s):  
Grain Boundary ◽  
Stress Corrosion ◽  
Stress Corrosion Cracking ◽  
Nitrate Solution ◽  
Corrosion Cracking ◽  
Low Alloy Steels ◽  
Intergranular Stress Corrosion ◽  
Oxidation Potentials ◽  
Alloy Steels ◽  
Impurity Elements

An important contributory role of grain boundary segregation of residual impurities in the intergranular stress-corrosion cracking of carbon and low alloy steels is proposed. Experimental results are presented of the stress corrosion susceptibility of mild steel in nitrate solution, and in relation to varying grain boundary composition as monitored by Auger electron spectroscopy. The harmfulness of a particular impurity element depends on three factors: its bulk level; its segregation thermodynamics and kinetics resulting in an equilibrium enrichment at the grain boundaries; and its ability to promote electrochemical dissolution of the grain boundary. A hierarchy of impurity elements that exacerbate stress corrosion cracking is presented and correlated with equilibrium oxidation potentials. The results and simple model allow the prediction of the relative harmfulness of impurity elements with respect to intergranular stress corrosion in commercial carbon and low alloy steels from a knowledge of the bulk concentration only. This enables significant improvements in performance to be designed in the alloy by respecifying lower levels of only the one or two highly detrimental impurities.

Mitigating the Stress Corrosion Cracking of Zircaloy-4 Fuel Sheathing: Siloxane Coatings Revisited

2016 ◽  
Vol 2 (2) ◽  
Author(s):  
Graham A. Ferrier ◽  
Mohsen Farahani ◽  
Joseph Metzler ◽  
Paul K. Chan ◽  
Emily C. Corcoran
Keyword(s):  
Wear Resistance ◽  
Stress Corrosion ◽  
Stress Corrosion Cracking ◽  
Nuclear Reactor ◽  
Corrosion Cracking ◽  
Candu Reactors ◽  
Graphite Coating ◽  
Water Reactors ◽  
And Performance ◽  
Graphite Coatings

For more than 50 years, a thin (3–20 μm) graphite coating has played an important role in limiting the stress corrosion cracking (SCC) of Zircaloy-4 fuel sheathing in CANDU® nuclear reactors. Siloxane coatings, which were examined alongside graphite coatings in the early 1970s, demonstrated even better tolerance against power-ramp-induced SCC and exhibited better wear resistance than graphite coatings. Although siloxane technology developed significantly in the 1980s/1990s, siloxane coatings remain unused in CANDU reactors, because graphite is relatively inexpensive and performs well in-service. However, advanced CANDU designs will accommodate average burnups, exceeding the threshold tolerable by the graphite coating (450  MWh/kgHE). In addition, siloxane coatings may find applicability in pressurized and boiling water reactors, wherein the burnups are inherently larger than those in CANDU reactors. Consequently, a commercially available siloxane coating is evaluated by its present-day chemistry, wear resistance, and performance in hot, stressful, and corrosive environments. After subjecting slotted Zircaloy-4 rings to iodine concentrations exceeding the estimated in-reactor concentration (1  mg/cm3), mechanical deflection tests and scanning electron microscopy (SEM) show that the siloxane coating outperforms the graphite coating in preserving the mechanical integrity of the rings. Furthermore, the baked siloxane coating survived a 50-day exposure to thermal neutron flux ((2.5±0.1)×1011  n/cm2 s) in the SLOWPOKE-2 nuclear reactor at the Royal Military College of Canada.

Sign in / Sign up

Export Citation Format

Share Document