Improved corrosion performance in super-duplex welds
Sukamal Naskar, Welding & Technical Expert (Sandvik Materials Technology), 8 Jul 2015
For demanding offshore oil and gas applications, duplex (UNS S31803) and super duplex (UNS S32750 and UNS S32760) stainless steels provide excellent corrosion resistance and high mechanical strength. When welding duplex and super-duplex steels, the biggest challenge is to maintain an optimized balance between the austenite-ferrite microstructure in the final weld metal as well as the desired mechanical properties. The purpose of this paper is to share our knowledge regarding the various practical fabrication aspects of duplex and super-duplex stainless steel welding. The paper provides practical advice on how to bring out the best of these complex materials as well as recommendations on how to retain the optimal balance of the duplex / super-duplex microstructure during and after welding.
Ten samples of super-duplex stainless steel pipe in two different sizes were welded and then tested by liquid penetrant test (LPT), radiographic test (RT) and finally ASTM G48 Method A corrosion bath test at 40°C for 24 hours. Based on these tests, this paper provides an overview of which temperatures, shielding and root gas mixes and other parameters are optimal to avoid the formation of any detrimental intermetallic phases or welding defects. The results of these tests are highlighted in the results section and summary.