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Laser and hybrid laser-arc welding of cryogenic 9%Ni steel for construction of LNG storage tanks

 
: Gook, Sergej; Forquer, Matthew; Gumenyuk, Andrey; Rethmeier, Michael; El-Batahgy, Abdel-Monem

:
Postprint urn:nbn:de:0011-n-3671552 (3.1 MByte PDF)
MD5 Fingerprint: 50de4bf09d9868f5c0c3b1e737f75ae4
Erstellt am: 27.11.2015


Egyptian Society for Laser Industrial Applications -ESLIA-; Osaka University, Joining and Welding Research Institute -JWRI-:
3rd International Conference in Africa and Asia on Welding and Failure Analysis of Engineering Materials, WAFA 2015. CD-ROM : Luxor, Egypt, November 2-5, 2015
Luxor, 2015
12 S.
International Conference in Africa and Asia on Welding and Failure Analysis of Engineering Materials (WAFA) <3, 2015, Luxor>
Deutsche Forschungsgemeinschaft DFG
01DH14012; LoWELL
Laserstrahl- und Laserhybridschweißen von vergüteten 9%Ni Stählen für Konstruktion von LNG-Anlagen aus sauberen Energiequellen
Englisch
Konferenzbeitrag, Elektronische Publikation
Fraunhofer IPK ()
cryogenic steel; laser welding; microstructure; hardness; tensile strength

Abstract
Heat treated 9%Ni steel is considered the most suitable and economic material for construction of large-size Liquefied Natural Gas (LNG) storage tanks which operate at cryogenic temperatures (-196°C). Strength above 700 MPa as well as a minimum impact value of 60 J are required to ensure reliable operation of the LNG tanks at operating temperature. Conventional arc welding processes including shielded metal arc welding (SMAW), gas metal arc welding (GMAW), gas tungsten arc welding (GTAW) and submerged arc welding (SAW) are currently used in construction of LNG tanks. Ni based filler wire is the preferred filler metal of choice in LNG tank construction. The main problem with this choice is the lower mechanical properties, particularly tensile strength of the weld metal. To compensate, the wall thickness needs to be excessively thick to ensure the strength of the welded structures. Ni based filler material is expensive and a large quantity is needed to fill the multi-pass weld grooves. These factors significantly add to the cost in the fabrication of LNG storage tanks. For these reasons, exploration of new welding technologies are a priority. A big potential can be seen in laser based welding techniques. Laser beam welding results in much smaller weld zone with chemical composition and mechanical properties similar to that of the base material. Laser welding is a much faster process and allows for a joint geometry which requires less filler material and fewer welding passes. The advantages of laser welding can help to overcome the problems pointed out above. Trials of autogenous laser welding, laser cold-wire welding and hybrid laser-arc welding (HLAW) conducted on the 9%Ni steel are presented in this paper. Chemical composition of the weld metal as well as effects of welding parameters on the weld formation, microstructure and tensile strength is discussed. Filler wire penetration depth as well as character of its distribution in the narrow laser welds was examined using Electron Probe Microanalysis (EPMA).

: http://publica.fraunhofer.de/dokumente/N-367155.html