ホールドリル法による実機残留応力測定技術の開発

(測定精度に影響を及ぼす因子の検討)

抄録

Stress corrosion cracking in nuclear power plants can be prevented by the shot peening process which gives compressive residual stress to the surface of components. Therefore, it is important to evaluate the residual stress distribution near the surface of the components. However, it is concerned that the residual stress induced by the peening may decrease during long term operation. For this reason, it is necessary to know the actual residual stress distribution after long term operation. After the East Japan Earthquake, several nuclear plants were decided to be decommissioned. By measuring the residual stress on the decommissioning components, it is possible to evaluate the change in the effect of the peening due to the long term operation. There are some techniques to measure the residual stress. Hole drilling method is relatively simple and inexpensive, and can also measure the residual stress distribution in depth. In the stress measurement by the hole drilling method, an error may occur depending on the state of the object to be measured or the measurement method. In this study, factors affecting the measurement accuracy in the stress measurement by the hole drilling method were considered. Experimental verification focusing on the drill hole position and hole diameter measurement error was conducted. As a result, it was found that decentering and hole diameter measurement accuracy are both factors that affect measurement accuracy by the hole drilling method. In particular, the effect of decentering was relatively large. However, even if these two factors were improved, errors were still observed the measurement inside the material. It should be necessary to consider further factors affecting the measurement accuracy by the hole drilling method in the future.