Remedial methods for intergranular attack of Alloy 600 tubing. Volume 1. Plant corrosion morphologies and remedial methods. Final report
This report evaluates the occurrence of intergranular attack (IGA) and stress corrosion cracking (SCC) of Alloy 600 tubing in PWR steam generators and reviews candidate remedial actions. Plant eddy current and tube pull data were examined to determine the morphology and location of corrosion. These data suggest that the affected plants fall into five categories: IGA occurring over a long axial length of the tube to tubesheet intersection; IGA and SCC localized at the top of the tubesheet; localized SCC within the tubesheet; SCC/IGA within tube support plate crevices; and SCC or IGA above the top of the tubesheet. Each category must be considered when selecting the inhibitor application mode. To determine which inhibitors might be effective, a review was performed of crevice deposit and crevice flushing solution analytical data taken from plants having SCC/IGA. From this review it was concluded that although there are some isolated instances of acidic sulfur induced SCC/IGA this form of corrosion is most often caused by an alkaline environment at specific electrochemical potentials. Thus SCC/IGA may be inhibited by neutralizing the alkaline environment, by moving the electrochemical potential out of the susceptible range, or by preventing the ingress of corrodent into the grain boundary and the egress of corrosion product out of the actively corroding grain boundary. Many potential IGA/SCC inhibitors are considered. However, the inhibitors identified have a significant disadvantage relative to boric acid because they are not plant qualified. On-line and off-line inhibitor application is discussed. A test plan for evaluating the inhibitors is outlined. 48 refs., 19 figs., 16 tabs.
- Research Organization:
- Westinghouse Electric Corp., Pittsburgh, PA (USA). Steam Generator Technology Div.
- OSTI ID:
- 5579841
- Report Number(s):
- EPRI-NP-4635-Vol.1; ON: TI86920387
- Country of Publication:
- United States
- Language:
- English
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36 MATERIALS SCIENCE
360105 -- Metals & Alloys-- Corrosion & Erosion
ALLOYS
BOILERS
CHEMICAL REACTIONS
CHROMIUM ALLOYS
CORROSION
CORROSION INHIBITORS
CRACK PROPAGATION
CREVICE CORROSION
INCONEL 600
INCONEL ALLOYS
INTERGRANULAR CORROSION
IRON ALLOYS
MATERIALS
NICKEL ALLOYS
NICKEL BASE ALLOYS
NIOBIUM ALLOYS
PWR TYPE REACTORS
REACTOR MATERIALS
REACTORS
STEAM GENERATORS
STRESS CORROSION
TUBES
VAPOR GENERATORS
WATER COOLED REACTORS
WATER MODERATED REACTORS