A study on process development of super-TIG welding for 9% nickel steel with Alloy 625

The demands for liquefied natural gas and 9% nickel steel tanks for its storage have increased due to stricter regulations for ship emissions. In the present study, a super-TIG welding process was developed for the butt welding of 9% nickel steel by using Alloy 625 filler metal with a C-type cross-section. The mechanical properties of the welded specimens were compared with those of flux-cored arc welding, using Hastelloy and Alloy 600 filler metals in impact and tensile tests, while the structures were examined under an optical microscope. The newly developed super-TIG welding process was shown to have an effective heat input ratio, given that hot cracking does not occur.