Assessment of intergranular corrosion in AISI Type 316L stainless steel weldments

Abstract

This paper deals with the applicability of various techniques for the assessment and quantification of sensitisation in AISI Type 316L welds. Welded joints of AISI Type 316L stainless steel were aged at 973 K for periods of up to 200 h. The base and weld metal components of the aged joints were then assessed for susceptibility to sensitisation and intergranular corrosion (IGC) by using various tests specified by ASTM A262, Practices A and E, and ASTM G108 (the electrochemical potentiokinetic reactivation (EPR) test). The possibility of using eddy current testing (ECT) to detect sensitisation and IGC was also assessed. The use of ASTM A262 Practice A and E tests indicated sensitisation in base metal aged for 20 h and above. Aged weld metals showed no failure in these tests. Tensile tests on the weld joints before and after exposure to Cu–CuSO₄-H₂SO₄ solution did not indicate any differences in the tensile properties. Double loop EPR tests indicated a significant increase in the ratios of charge and peak current densities on reactivation to activation after aging the welded joint for 20 h and above. However, weld metal showed no change in the ratios of the above two parameters. Following doubts about the suitability of the EPR test for on line corrosion monitoring, the ECT technique was investigated in order to assess its suitability for the detection and quantification of sensitisation. The ratio of eddy current amplitudes after and before exposure to Cu–CuSO₄-H₂SO₄ solution was used as an assessment criterion. A significant increase in this ratio was observed on aging the base metal for more than 20 h. No significant change was observed in the ratios of eddy current amplitudes for weld metal. The ECT results correlated very well with the findings of the EPR and ASTM Practice E tests. This indicates that ECT holds promise as an on line monitoring tool for sensitisation and IGC.