Stress Corrosion Cracking of Lean Duplex Steel in 3.5% Sodium Chloride Solution

Abstract

Duplex stainless steels (DSS) exhibit attractive combination of austenitic and ferritic properties and have been extensively used in various industries such as petrochemical, pulp and paper etc. They demonstrate better corrosion resistance, especially chloride stress corrosion and chloride pitting corrosion, and exhibit higher strength than standard austenitic stainless steels. For these reasons, they are excellent candidate for offshore oil and gas industry. In the present study, stress corrosion behaviour of duplex stainless steel in 3.5% sodium chloride solution, has been investigated by weight loss measurements, electrochemical corrosion testing and slow strain rate test (SSRT). Weight loss data showed no significant corrosion after 1700 hours. Electrochemical polarization test in 3.5% NaCl solution exhibited a uniform corrosion rate of 0.008 mpy showing passivity in the range of 735–950 mV Vs SSC. A comparison of the slow strain rate test for duplex stainless steel in 3.5% NaCl solution also showed a similar stress-strain behaviour. In contrast, the stress-strain behaviour of mild steel showed a loss of about 25% elongation. The excellent corrosion and especially the pitting resistance was considered to be responsible for maintaining good ductility in DSS.