Effects Assessment of Preemptive Weld Overlay of Nuclear Pipes
Date Issued
2009
Date
2009
Author(s)
Liu, Yao-Chi
Abstract
Weld overlay (WOL) repair technique has been used in U.S. nuclear industry for years. In particular, preemptive weld overlay (PWOL) is frequently applied to areas of dissimilar metal welds (DMW) to avoid fracture of nuclear power plant components. Although a lot of researches and assessments related to PWOL have been carried out in recent years, they are primarily done in foreign countries, and the environmental situation may not be the same as the local one. In the present study, domestic environmental and operational conditions are taken into consideration to assess the effect of preemptive weld overlay of nuclear power plant components. Finite element method (FEM) is employed to find the residual stresses and probabilistic fracture mechanics analysis is adopted to evaluate the failure probabilities due to fatigue crack growth. Welds at the pipe of spray nozzle of a pressurized water reactor (PWR) is illustrative as an example. It is found from finite element analysis that residual stresses at the weld on inner surface of the pipe is changed from tensile to compressive after carrying out the weld overlay. It indicates that PWOL reduces the possibility of crack growth. The result of the probabilistic fracture mechanics analysis also indicates that, after 40 years of operation, the failure probability at welds of the pipe changes from order of 10-4 to 10-6 after employing PWOL. It further ensures the applicability of PWOL to local nuclear power plant components or, at least, to the pipe of the studied spray nozzle.
Subjects
Weld Overlay
Preemptive Weld Overlay
Reliability
Probabilistic Fracture Mechanics
Type
thesis