因核能電廠中大量使用雙相不鏽鋼金屬於反應鍋爐以及管路之中，所以對於雙相不鏽鋼金屬的安全考量就變得相當重要，但核能電廠的工作環境會處於一個相對高溫的狀態，因此會導致雙相不鏽鋼金屬產生熱時效脆化，使雙相不鏽鋼金屬中的金相開始產生相變化，導致雙相不鏽鋼金屬的劣化，進而影響核能電廠的運轉安全性，本論文將使用超音波檢測技術針對雙相不鏽鋼金屬進行特性評估。
本論文建立了兩套不同的超音波檢測系統，其一是使用無鏡頭式線聚焦換能器搭配V(f,z)散焦量測，量測有關雙相不鏽鋼金屬老化時間與波速及衰減量的關係，其二為利用雷射超聲波系統搭配刀緣檢測法量測不同老化時間之雙相不鏽鋼金屬，使用交叉相關法分析表面波波速，觀察其特性，以及分析刀緣檢測法中，聚焦光點對於量測訊號品質的影響。

Abstract

Because the nuclear power plants use a lot of duplex stainless steel in boiler and pipeline, the security concerns become very important. The nuclear power plant operating temperature is relatively high, it induces the thermal aging embrittlement and makes the metallographic of duplex stainless steel phase transformation. If the duplex stainless steel generates deterioration, the nuclear power plant security will be doubted. So this study uses the ultrasonic inspection to characterize the aged duplex stainless steel.
This study constructs two different ultrasonic inspection systems. One is using the lens-less line-focused transducer along with a V(f,z) defocusing measurement system to detect the aged time, wave speed and decrement of duplex stainless steel. The other is using laser ultrasonic systems along with knife edge method to detect the duplex stainless steel of different aged times. We use the cross-correlation method to analyze the surface wave speed and observe its characterization and also discuss the influence of the focus point for detecting signal quality in knife edge detecting method.

Summary

Non-destructive testing is a kind of analysis technique widely used in industry to evaluate the characterization of a material. Because of the high yield stress and well corrosive resistance, the duplex stainless steel is widely used for the boiler and high pressure pipeline. Because the high temperature environment will make the duplex stainless steel brittle and then cause the damage or crack, its life time is the most important topic should be concern about. In this thesis, two non-destructive testing method is constructed to observe the properties of aged duplex stainless steel. One of the method is that using lens-less line-focused PVDF transducer combine with defocusing measurement method to measure surface acoustic wave (Rayleigh wave) velocity and attenuation. Another one is laser ultrasound technique. By using these two method, its experimental result can conclude some characteristic tendency. With the increase of the aged time, the quantity of attenuation of duplex stainless steel is increased. In the knife-edge measurement system of laser ultrasound technique, the smaller detection spot size can get better acoustic wave signal.

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