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Steel Designers' Manual - 6th Edition (2003)
690 Welds and design for welding
to have 27J at -20°C. Moving in the direction of lower test temperatures however
is acceptable.
Steelwork contractors should always be seeking cost reduction, but cheaper steels
with inferior quality generally lead to more expensive welds, especially if lamellar
tearing is a possibility. Many connections require good through-thickness ductility
to avoid tearing, and non-destructive testing before welding does not reveal these
potential problems. Furthermore, impurities at levels well below the specified
maxima will reduce impact toughness. Inferior rolling and levelling practices will
cause dimensional problems when the steel is cut and welded. Moving to cheaper
steels rarely saves overall costs.
24.2.4 Standards – welding processes and practices
BS EN 1011-2: 200l 4 provides guidance for welding practices used in the various
codes for buildings and bridges, especially in the avoidance of cold cracks, hot cracks,
and other unacceptable discontinuities. Significantly, it provides the fabricator with
the means to estimate preheat temperatures required to avoid cold cracking caused
by hydrogen, and it contains guidance on acceptance levels for weld discontinuities.
When making recommendations to avoid cold cracking BS EN 1011 incorporates
the principles of diffusible hydrogen content of the weld metal, the carbon equivalent
value (CEV) of the parent metal, the combined thickness of the members
of the joint being welded, the heat input (determined from the energy input to
the weld), and the preheat temperature. The recommendations of BS EN 1011 are
incorporated into a Welding Procedure Specification (WPS) to be followed during
welding. This ensures that weld properties and soundness (for example the absence
of cold cracking, controlled by the combination of carbon equivalent value,
combined thickness, diffusible hydrogen content and preheat temperature) are
achieved.
24.2.5 Welding standards – welding consumables
A harmonized set of European standards provides common designations for the
yield strength and impact energy of weld metal deposited by the consumables used
by the various processes, and additional information specific to the processes
(shielding gas, flux type, etc).
BS EN 440: 1995, 13 Wire electrodes and deposits for gas shielded metal arc welding
of non alloy and fine grain steels. Classification
BS EN 439: l994, 14 Shielding gases for arc welding and cutting
BS EN 499: 1994, 15 Covered electrodes for manual arc welding of non-alloy and
fine grain steels. Classification