Circumferential Notch Tensile Testing: Role of Imposed Electrochemical Potentials in Susceptibility of Steel to Caustic Cracking

Abstract

A fracture mechanics based novel approach, i.e., circumferential notch tensile (CNT) testing has been employed for determination of threshold stress intensity factor for susceptibility of engineering materials to stress corrosion cracking . Using CNT technique, of a mild steel at an open circuit potential in NaOH at was determined to be . CNT tests have also been performed under imposed electrochemical potentials to understand the mechanistic aspects of caustic cracking as well as to develop guidelines for mitigation of caustic cracking. An imposed potential in the active-passive potential regime caused much more rapid failure (than was observed at ). The fractography of the CNT specimens tested at and showed evidence of stress corrosion cracking. At an imposed potential in the passive region , the specimen did not fail even after an order of magnitude longer testing, indicating a considerable improvement in resistance to caustic cracking as a result of this application of . The resulting fractograph confirmed the absence of caustic cracking. The study has established the use of CNT testing as a simple, relatively fast and economical approach for generating the data, and showed that the data are consistent with an electrochemical mechanism for caustic cracking.