Metallurgical factors that contribute to cracking in BWR piping
During the fall of 1974 and early winter of 1975, cracks have been discovered in the 4 in. bypass lines of several Boiling Water Reactors (BWR's) in the United States. Further, similar cracks were discovered at two BWR's in Japan during the same period. More recently, cracks have been discovered in the core spray piping and in a furnace-sensitized ''safe end'' and adjacent ''dutchman'' at the Dresden Nuclear Power Station, Unit No. 2. Although inspections at all other U.S. BWR's have not disclosed further instances of cracking in core spray piping, leaking cracks have been found in the core spray piping of two BWR's overseas. Metallurgical examinations of these cracks are not yet complete. The following observations have been made to date. All cracks (except those in the furnace-sensitized safe end and dutchman) occurred in seamless type 304 stainless steel piping or in elbows fabricated from such piping, in the outer heat affected zone of either field or shop welds, in lines isolated from the main primary coolant flow during full power operation, except for the not yet examined cracks in the Monticello bypass lines. The cracks are exclusively intergranular, and occur in metal that has been lightly sensitized by the welding process, with only intermittent grain boundary carbides. They developed in the areas of peak axial residual stresses from welding rather than in the most heavily sensitized areas. No fatigue striations have been found on the fracture surfaces. The evidence received to date strongly indicates that these cracks were caused by intergranular stress corrosion of weld-sensitized stainless steel by BWR water containing greater than 0.2 ppM oxygen. The possible role of fatigue or alternating stresses in this corrosion is not clear. Further, not all the cracks detected to date necessarily have occurred by the same mechanism.
- Research Organization:
- Brookhaven National Lab., Upton, N.Y. (USA)
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 7284546
- Report Number(s):
- BNL-NUREG-21102
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
210100* -- Power Reactors
Nonbreeding
Light-Water Moderated
Boiling Water Cooled
ALLOYS
BWR TYPE REACTORS
CHEMICAL REACTIONS
CHROMIUM ALLOYS
CHROMIUM STEELS
CHROMIUM-NICKEL STEELS
COOLING SYSTEMS
CORE SPRAY SYSTEMS
CORROSION
CORROSION RESISTANT ALLOYS
CRACKS
DEFECTS
ECCS
ENGINEERED SAFETY SYSTEMS
HEAT RESISTING ALLOYS
INTERGRANULAR CORROSION
IRON ALLOYS
IRON BASE ALLOYS
NICKEL ALLOYS
PIPES
REACTOR COMPONENTS
REACTOR COOLING SYSTEMS
REACTOR PROTECTION SYSTEMS
REACTORS
STAINLESS STEEL-304
STAINLESS STEELS
STEELS
STRESS CORROSION
WATER COOLED REACTORS
WATER MODERATED REACTORS