In situ heat treatment of U-bends: Final report
Row 1 nuclear steam generator tubes of mill annealed Alloy 600 tubing were stress relief annealed at 1450/sup 0/F for 15 minutes using a special internally placed flexible electrical resistance heater. The U-bends were strained to simulate differential thermal expansion stresses and tested for primary water stress corrosion cracking (PWSCC) resistance in two reference accelerated test environments (680/sup 0/F high purity water and 750/sup 0/F superheated steam), both of which contained hydrogen partial pressures. Prototypical axial throughwall cracking at the extrados of the irregular U-bend transition tangent was produced in base line, non-stress relieved U-bends, while no throughwall cracking occurred in any stress relieved sample. An improvement in PWSCC resistance due to this stress relief of at least a factor of 30 can be inferred for the 7/8 in. tubing material that was of a highly PWSCC susceptible heat. The 3/4 in. tubing material, which was more resistant to PWSCC in the mill annealed condition, exhibited an inferred factor in PWSCC resistance, due to the 1450/sup 0/F stress relief, or at least 11. The program identified and qualified a lower temperature, shorter time, stress relief cycle of 1300/sup 0/F for five minutes. Accelerated PWSCC testing in 750/sup 0/F steam indicated that 7/8 in. OD U-bends stress relieved at 1300/sup 0/F for five minutes exhibit a resistance to PWSCC that is at least 100 times greater than as-bent samples that were readily cracked in the steam exposures. It is concluded that in-situ stress relief of mill annealed Alloy 600 nuclear steam generator U-bends is highly beneficial in reducing, or possibly eliminating, PWSCC at the U-bend tangent points where instances of PWSCC have been documented in operating plants. 10 refs., 44 figs., 16 tabs.
- Research Organization:
- Westinghouse Electric Corp., Pittsburgh, PA (USA)
- OSTI ID:
- 5829541
- Report Number(s):
- EPRI-NP-5496; ON: DE88920076
- Country of Publication:
- United States
- Language:
- English
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36 MATERIALS SCIENCE
360103 -- Metals & Alloys-- Mechanical Properties
360105 -- Metals & Alloys-- Corrosion & Erosion
ALLOYS
BENDING
BOILERS
CHEMICAL REACTIONS
CHROMIUM ALLOYS
CORROSION
CRACK PROPAGATION
CRACKS
ELEMENTS
HEAT TREATMENTS
HYDROGEN
HYDROGEN COMPOUNDS
INCONEL 600
INCONEL ALLOYS
IRON ALLOYS
NICKEL ALLOYS
NICKEL BASE ALLOYS
NIOBIUM ALLOYS
NONMETALS
OXYGEN COMPOUNDS
PWR TYPE REACTORS
REACTORS
REPAIR
STEAM
STEAM GENERATORS
STRESS CORROSION
TESTING
TUBES
VAPOR GENERATORS
WATER
WATER COOLED REACTORS
WATER MODERATED REACTORS