Assessment of design basis for load-carrying capacity of weld-overlay repairs
This study was conducted to assess the current load-carrying capacity design basis for weld-overlay repairs (WORs). Although not specifically addressed in it, the design of WORs is in the spirit of the ASME Boiler and Pressure Vessel Code, Section XI, Article IWB-3640. NUREG-0313 Revision 2 provides guidance for the implementation of the procedures outlined in IWB-3640. However, neither of these documents specifies the values for diameter or thickness which are to be used in the WOR design analysis. Throughout this report we have used the combined thickness and diameter of the repaired cross section to calculate the membrane and bending stresses. The maximum stress from each of the four WOR pipe experiments conducted was significantly higher than that predicted by the IWB-3640 analysis for the design guidelines set forth in NUREG-0313 Revision 2 for a Standard overlay; the average failure stress was approximately 30% higher than the IWB-3640 predicted failure stresses. Consequently the actual safety factors were 30% higher than safety factors used in the Code. For a Standard overlay, the flaw size considered in the analysis is completely through the original pipe wall for the entire circumference of the pipe. Such an overlay would be suitable for long-term plant operation. If actual flaw dimensions were used in the design analysis, then in two of the four experiments the maximum stress was less than that predicted by the IWB-3640 Source Equations. The greatest difference showed that the actual safety factor was 8% lower than the Code safety factor. For the flaw sizes evaluated in this study, an overlay design based on actual flaw dimensions would be considered a Limited Service overlay, suitable only for short-term plant operation, not to exceed one fuel cycle.
- Research Organization:
- Battelle Columbus Labs., OH (USA); Nuclear Regulatory Commission, Washington, DC (USA). Div. of Engineering Safety
- OSTI ID:
- 6499277
- Report Number(s):
- NUREG/CR-4877; BMI-2150; ON: TI87900636
- Country of Publication:
- United States
- Language:
- English
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36 MATERIALS SCIENCE
360103 -- Metals & Alloys-- Mechanical Properties
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ALLOYS
ARC WELDING
BWR TYPE REACTORS
CHARPY TEST
CHEMICAL REACTIONS
CHROMIUM ALLOYS
CORROSION
CORROSION RESISTANT ALLOYS
CRACK PROPAGATION
CRACKS
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METALLOGRAPHY
PIPES
REACTORS
REPAIR
STAINLESS STEELS
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STRESS CORROSION
TESTING
WATER COOLED REACTORS
WATER MODERATED REACTORS
WELDED JOINTS
WELDING