Abstract
A thermal fatigue surface crack (6 mm deep × 23 mm wide) in a thick austenitic stainless steel plate is opened and closed with thermal heating and cooling cycles. This closing and opening of the crack is recorded with using fundamental wave amplitude difference (FAD) technique with 5 MHz 64 element phased array probe. In addition, the contact pressure and crack opening state at different time intervals were estimated using finite element (FE) simulation. In combination with the nonlinear output from the FAD and FE simulation gave insight at which level the contact pressure or the distance between crack faces prevents the contact acoustic nonlinearity (CAN) from happening. Predictably, no clear nonlinear response was recorded at crack face locations experiencing high contact pressure and on the locations where the crack could be considered fully open, as predicted by the FE simulation. Therefore, the FAD technique can be utilized within the constraints quantified in the paper.
Highlights
Nuclear power plants (NPPs) have been built for long term use and as this long term use is extended beyond the original design life, reliable non-destructive inspections (NDI) have a huge impact on the safe operation of the NPPs
We present an instrumented thermal fatigue experi ment where a surface crack is periodically opened and closed with different loading rates and heat inputs
The nonlinear effect is diminished if the crack faces are too far apart
Summary
Nuclear power plants (NPPs) have been built for long term use and as this long term use is extended beyond the original design life, reliable non-destructive inspections (NDI) have a huge impact on the safe operation of the NPPs. Austenic stainless steel materials are widely used in critical components such as primary circuit piping. Austenic stainless steel materials are widely used in critical components such as primary circuit piping These components are usually inspected with ultrasonic testing to detect possible cracking caused by the thermo-mechanical loads and corrosive environment. When such cracks are found, proper sizing of the indications is critical for accurate assessment of the flaw acceptability. The linear response from an open crack is mainly based on the difference between the acoustic impedance of two different me diums. Traditional linear ultrasonics focus only on this central frequency [1,2,3]
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