Characterisation of Intergranular Corrosion in Austenitic Stainless Steel using Lock-in Thermography

Intergranular corrosion (IGC) is one of the major localized corrosion problems faced by austenitic stainless steel (SS) components used in various industries. Conventional non-destructive methods such as ultrasonic, eddy current, radiography, etc., have the limitations in detecting the onset of localized corrosion, particularly at the earlier stage to have better understanding of the phenomenon. Hence, the use of lock-in thermography method to detect and monitor IGC at an early stage was explored in this work. AISI types 304 and 304LSS were subjected to sensitization heat treated at 675 degrees C for 30min, 1hr, 10h, 100h, 250h and the IGC resistance was evaluated as per ASTM A262 Practice A (oxalic etch test) and double loop potentiokinetic reactivation (EPR) method. This paper dwells on the experimental approaches and the results obtained. Lock in thermography clearly indicates that it is a potential tool for early detection of sensitisation.