CEMP-E
TI 809-26
1 March 2000
aluminum, nitrogen, carbon and other alloying elements. When weld processes that use consumables
with significantly different metallurgical systems are mixed with FCAW-S deposits, there is the potential
for reduced properties, particularly ductility and toughness. This is the result of the liberation of nitrogen
and aluminum that were previously chemically combined as Al-N in the FCAW-S deposit. Other weld
deposits, typically a carbon-manganese-silicon metallurgical system, do not contain the amount of
aluminum necessary in order to preclude the formation of free nitrogen, which can embrittle the steel or
weld deposit.
b. Investigation. When it is suspected that existing weld deposits that will receive subsequent welding
were made using FCAW-S, further investigation of the weld deposit is warranted. An aluminum content
in the range of 1% is indicative of FCAW-S. Low-admixture welding procedures, design assuming
reduced mechanical properties, or requiring subsequent welding using appropriate FCAW-S should be
considered.
c. Other Processes. Recent research indicates that this problem may not be limited to non-FCAW-S
weld deposits on top of FCAW-S. Multiple weld processes in a single weld joint may also occur in new
construction because of tack welding, root pass welding selection, or other reasons.
5. STRENGTH REDUCTION EFFECTS AND OTHER CONCERNS WHEN WELDING UNDER LOAD.
a. Elevated Temperature Effects. Elevated temperatures in steel reduce both the yield strength (Fy)
reduced approximately 20%. Preheat temperatures at this level are rarely used, but localized
temperatures near the weld region will exceed these temperatures for brief periods. As a general guide,
steel during welding, within the weld region, will exceed these temperatures approximately 25 mm (1 in.)
to the side of a weld, and a distance of approximately 100 mm (4 in.) trailing the weld puddle. Steel
further from the weld region will remain at temperatures that will not significantly reduce the steel's
properties.
b. Welding Direction and Sequence. When welding under load, consideration should be made for the
temporarily reduced strength of localized areas of the steel. When welding parallel to the applied stress,
the affected area is typically small compared to the area of the unaffected steel. When welding
transverse to the load, additional caution is needed. It may be necessary to stagger welding operations,
use shorter sections of weld and then allow cooling, or use lower heat input procedures.
6. HAZARDOUS MATERIALS.
When welding on steel having existing coatings, an investigation into the composition of the coating is
warranted, unless all coatings in the vicinity of the welding are removed prior to welding. Zinc, used in
numerous coating systems and galvanizing, produces noxious fumes. Some older structures may contain
lead-based paints that must be removed using special hazardous materials precautions.
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