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Evaluation of the technical basis of justification for continued operation of power plant components - Flaw evaluation for in-service inspection indications
- Linear and non-linear stress analysis
Flaw Evaluation of a Linear Indication in the Seat Ring of a Swing Check Valve
APTECH conducted a flaw evaluation where there were no explicit ASME rules for valves in the Code. We used a conservative model and the methodology and acceptance criteria for vessels and piping in the Code for guidance. The evaluation included analysis of fracture toughness, stress analysis, critical flaw size, and projected fatigue crack growth under both operating and accident conditions. The valve was determined to be structurally acceptable for continued service for the evaluation period without repair.
Flaw Evaluation of Weld Indication in Steam Generator Transition Cone Shell
An engineering evaluation was conducted of a subsurface weld flaw discovered during routine inspection of a steam generator. Because the size of the indication exceeded ASME inspection acceptance standards, APTECH was requested to perform a detailed flaw analysis. A finite element stress analysis was made considering both pressure and thermal loads and the results were used in the fracture mechanics evaluation. The flaw was demonstrated to be acceptable under ASME rules, without repair, for the remaining design life of the plant.
Justification for Continued Operation (JCO): JCO 89 012 Revision 2 Containment Air Coolers
To evaluate joint integrity, APTECH thoroughly reviewed leak history, past corrective actions, design, and stress analyses which had been performed by the customer and another engineering firm. Additionally, inspection and testing procedures as well as daily operating procedures were reviewed to assess the consequences of future leaks. Aptech recommended additional inspections of new joints to increase the statistical basis for projections and to assure early identification and removal of substandard joints.
The Significance of Lack of Penetration/Lack of Fusion in ASME Class 3 Piping Welds
APTECH conducted a combined statistical and "worst case" deterministic analysis of the significance of specific weld flaws. Aptech used fracture mechanics and limit load concepts to assure compliance with ASME Section III allowables for degraded pipe sections and assessed structural integrity using ASME Section XI methods. Analysis used highest stressed nodes, bounding flaw sizes, and assumed the flaw was placed at the worst location in the pipe section for stress. Welds identified by this conservative method as needing further evaluation were radiographed to ensure compliance with Code requirements. Additional analysis identified one substandard welder, whose welds were all radiographed and corrective actions taken where necessary.
Evaluation of Saw Cuts in Coped Beams
APTECH evaluated the load carrying ability of 12 structural beam connections which had been fabricated with saw cutting. These copes generally had been cut to a square corner and some had a notch in the corner as a result of saw overrun. Three levels of conservatism were defined in the methodology: defining a critical flaw size for all beams of a given size, determining a critical flaw size for a specific beam under generic load conditions, and evaluating beam specific loading. APTECH developed a computer program that was used as the basis for this generic analysis yet still allowed for beam specific analysis if needed. All beams were determined to meet the acceptance criteria for their specific beam type as is.
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