Artificial flaw simulation in ultrasonic inspection of austenitic stainless steel weld:Master's thesis

Nuclear power plant primary circuit components are made from austenitic stainless steels. They provide mechanical properties combined with corrosion resistance and weldability. The structural integrity of the components needs to be verified to allow the safe operation of nuclear power plants. Austenitic stainless steel welds are inspected with ultrasound. The austenitic weld distorts, attenuates, deviates and scatters the ultrasonic beam making the inspection difficult.When conducting ultrasonic inspection at the power plants, the time allowed for the in- spection is short as the components are only accessible during outages. Due to the limited time and required qualifications, the inspection plan and procedure are validated before- hand. The ultrasonic method is verified using test block, but acquiring test blocks with service induced flaws is difficult. Instead, mock-ups can be used. Producing real like flaws in the mock-ups is also expensive and time consuming. Artificial flaws, like elec- trical discharge machined (EDM) notches can be used as more cheap alternatives. Simu- lation is also a possibility to verify the methods of ultrasonic inspection.The aim of this thesis is to study the validity of ultrasonic simulations in austenitic stain- less steel weld. An existing test block with five EDM notches is inspected and then the same procedure is carried out in a CIVA simulation. The simulation is done with smooth flaws and flaws that have surface roughness. The results of the carried out measurements are compared with the results of the simulations