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In welding thinner plates, the microstructure of the
weld commonly tends to be coarse because of slower
cooling speeds and fewer required weld passes. Fig. 2
shows Charpy impact test results of LB-52NS weld
metals with three different plate thicknesses using the
groove preparation and weld pass sequence shown in the
figure.
It is obvious that LB-52NS provides adequate notch toughness, even in the severe condition of vertical-up welding, over a range of plate thicknesses, although with thinner base metal, notch toughness is lower with almost the same heat input. This is because the thinner the base metal, as shown in Table 1, the slower the cooling speed. Slower cooling speeds can cause more or less coarse microstructure, thereby decreasing notch toughness. Table 1 - Plate thickness, heat input and cooling speed in Charpy impact test of LB-52NS weld metals
LB-52NS Maintains Adequate Tensile Strength over Extended PWHT
Fig. 3 - Fig. 3 - Effect of PWHT conditions on tensile properties of LB-52NS deposited metal
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In welding fabrication of thick-section pressure
vessels, postweld heat treatment (PWHT) is
indispensable to relieve residual stresses raised by
welding. As with typical ferritic weld metal, the tensile
and yield strengths of LB-52NS deposited metal
decreases as PWHT temperature or soaking time
increases, reducing residua] stresses. However, LB-
52NS maintains adequate tensile strength and yield
strength even after extended PWHT as shown in Fig. 3.
This preferable characteristic is derived from fine-
microstructure weld metal provided by the sophisticated
design of chemical composition as previously
mentioned.
LPG Storage Tank is Typical Application of LB-52NS
Fig. 4 - Cylindrical LPG storage tank is a typical application of LB-52NS Liquefied petroleum gas (LPG) is stored at a low temperature of minus 45*C in thermal-insulated LPG storage tanks. Therefore, materials including weld metal of the tank must have adequate notch toughness at that temperature. In construction of a cylindrical LPG tank, in addition to automatic processes (SAW, GTAW), LB- 52NS is an indispensable electrode featuring unsurpassed quality including usability in out-of- position welding and resistance to cold cracking and moisture pick-up. |