Insight into the galvanic corrosion behaviour of low alloy steel A508/309 L/308 L stainless steel dissimilar metal weld at different temperatures.

Abstract

Galvanic corrosion is prevalent in many dissimilar metal welds (DMW) in-service applications. Nevertheless, there is a scarcity of systematic investigations regarding the effect of different temperature conditions on the galvanic corrosion behaviour of low alloy steel (LAS)/309 L/308 L stainless steel (SS) DMW making up the reactor pressure vessel (RPV). Relevant results of this study indicate that temperature significantly affects the galvanic corrosion behaviour of LAS A508/309 L/308 L SS in simulated primary water solution. The shutdown temperature condition showed a higher influence of galvanic corrosion than the operating temperature condition. The discrepancy is ascribed to the varying difference in corrosion potential between the dissimilar metals in both conditions, which are 357 mV vs. SCE and ⁓55 mV vs. SCE for shutdown and operating temperature conditions, respectively. The specially designed immersion test simulating the actual RPV in-service environment revealed that the galvanic interaction between the dissimilar metals at the interface region is greatly affected by the anode (LAS A508) to cathode (309 L/308 L SS) area ratio, with average corrosion exceeding 0.3 mm/y occurring when the actual anode to cathode area ratio exceeds 1:6000. Finally, from the morphological evolution results it is seen that galvanic corrosion develops along the weld fusion line interface, rather than in the depth direction of the LAS A508, which is conducive for the operational reliability of the RPV.