Reliability Of Eddy Current Nondestructive Testing For Defects On Austenitic Stainless Steel

Austenitic stainless steel has good comprehensive properties,can exhibit high corrosion resistance in oxidizing environment,and excellent toughness at low and high temperature environments.Therefore,it is widely used in equipment manufacturing in chemical,aviation,nuclear power and other industries.Austenitic stainless steel due to its own material composition,working environment and other special factors,the surface will also occur corrosion phenomenon.In order to effectively prevent the damage to the equipment caused by corrosion,non-destructive testing technology came into being.NDT commonly used detection methods include ultrasonic testing,magnetic particle testing,radiographic testing,penetration testing and eddy current testing.Compared with other detection methods,eddy current testing can achieve non-contact detection,no coupling agent,automatic detection and other advantages.In this study,the eddy current testing method was used to detect the defects of austenitic stainless steel cladding.However,the detection signal will be affected by many factors during the detection process,such as human factors,environmental factors,specimen surface roughness and so on.Due to the existence of these influencing factors,it is impossible to determine whether the defect is effectively detected during the defect detection process.Therefore,the probability of detection(POD)is used as an index to quantitatively evaluate the ability of eddy current probe to detect defects.In this study,the traditional POD model was improved,and a new POD model was proposed.Nine plate samples with austenitic stainless steel cladding were prepared.The drilled holes with different sizes were artificially drilled on the surface of plate samples to simulate the pitting corrosion on the inner surface of the equipment.Three different types of eddy current probes were used to detect noise and defects,and new POD model was used to evaluate the detection ability of three different types of eddy current probes for defects on the austenitic stainless steel cladding.Through the analysis of the experimental results,the following conclusions are drawn.Firstly,the new POD model proposed in this paper combines more factors(decision threshold selection,etc.)to detect the surface defects of austenitic stainless steel cladding,which is better than the traditional POD model.Second,for three different types of probes,Uniform probe has the best detection ability for surface defects of austenitic stainless steel cladding.Uniform probe can better suppress the high level and uneven noise caused by the uneven surface of the cladding and has a better signalnoise detection ratio.It can reliably detect defects larger than 1.4828 mm on the austenitic stainless steel cladding.