PRODUCTIVITY UP. COSTS DOWN.
Productivity and cost benefits of application of nickel-based flux-cored wire with DC+ and AC-current for the vertical up welding of 9 % Nickel LNG storage tanks
Welded joints in the fabrication of cryogenic liquid nitrogen gas (LNG) tanks are submitted to severe conditions – such as very low temperatures and high stress. Welding of these joints comes with stringent requirements on weld metal strength and toughness. Products from voestalpine Böhler Welding offer high quality solutions for commonly applied alloys such as:
- 9 % Ni steel
- Austenitic steel with cryogenic properties
- Low-temperature construction steel
The voestalpine Böhler Welding portfolio for welding of 9 % Ni steel covers all commonly applied processes (SAW, SMAW, GMAW and FCAW). Only nickel-based weld metal can match the strength of the steel with good ductility at LNG service temperatures of about -170 °C in the as welded condition.
An additional advantage is that nickel-based consumables reduce the risk of hydrogen induced cracking, as they deposit an austenitic weld metal. Basic SMAW electrodes, such as UTP Soudonel D and SAW wire and flux combinations, such as Thermanit NiMo C276 & Marathon are frequently used, which give a clean deposit with very low levels of micro slag inclusions. Typical requirements for welding consumables are given by API 620 Appendix Q, ASME/AWS and BS 7777. These specify strength levels of Rp0.2>430 MPa and Rm>690 MPa, while project specifications for Charpy V-notch (CVN) impact toughness can be greater than 70 J at -196 °C, with lateral expansion greater than 0.38 mm. In addition, CTOD (cracktip opening displacement) fracture toughness values may be specified for resistance to crack lengths down to 0.3 mm at cryogenic temperatures of -170 °C.
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