| ‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘ KAWASAKI STEEL TECHNICAL REPORT No.5 ( May 1982 ) ‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘‘ |
| Development of the Narrow Gap Submerged Arc Welding Process - NSA Process
Yukio Hirai, Masaaki Tokuhisa, Itaru Yamashita, Kaname Nishio, Kozo Akahide, Teruo Ukebe |
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Synopsis : With main emphasis on improving slag detachability and preventing weld defects in a narrow gap groove, study was made on the submerged arc welding of heavy steel plate, leading to the development of the NSA process that uses an MgO-BaO-SiO2 type high-basicity agglomerated flux, KB-120. With thermal contraction behavior of slag found to be the most important factor that determines slag detachability, the maximum contraction was obtained by suppressing transformation expansion occurring around 700 during cooling. It was found that KB-120 can also produce weld metal of low level hydrogen and oxygen. High reliability and productivity of this process has been confirmed by its wide application to the fabrication of pressure vessels, offshore structures and machinery. Since the "one layer-one pass" welding technique is used to build up for steel plates up to 200mm in thickness, the cross sectional area of the groove and arc time are reduced to 1/2 to 1/3 of those in the conventional process. The use of very low hydrogen flux provides additional advantages such as elimination of intermediate post-weld heat treatment and lowering of preheating temperature. |
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