Ducting installation work.... #hvac #chiller #ductwork #ahu #india #motivation #motivational

GI pipe welding
Welding galvanized iron (GI) sheets requires special consideration due to the zinc coating. The best method is to use a process called "spot welding" or "MIG welding" (Metal Inert Gas) with appropriate precautions: 1. **Spot Welding**: Spot welding is often the preferred method for welding GI sheets..
QUALITY OF
WELDED JOINTS
Welding procedures are described in
this paper for obtaining sound joints in
zinc coated steels. It is necessary to
consider the mechanical properties of sound welds on zinc coated steel and
also the mechanical properties of
welded joints containing typical de-
fects that can be caused by the pres-
ence of the zinc coating.
It is not uncommon to find small
cracks in a fillet weld on galvanized
steel, extending from the root toward the
face of the bead. Whether cracking will
occur depends on many factors such as
the silicon content of the weld metal, the
degree of penetration of the weld, the
thickness of the base metal that influ-
ences restraint of the joint, and the coat-
ing weight of the zinc and the mi-
crostructure of the zinc coating, which
are both influenced by the composition
of the base plate, particularly with re-
spect to silicon content. Low-silicon or
rutile (non-low-hydrogen) base elec-
trodes with low silicon content (0.2Si or
lower) generally reduce cracking.
Undercut is the most prevalent de-
fect found in fillet welds deposited in
the horizontal and vertical positions
with either rutile or basic covered
electrodes. This defect can occur at ei-
ther side in vertical welds, but in the
horizontal position, it generally is re-
stricted to the vertical plate.
Undercut is more likely to occur
with rutile electrodes when the slag is
allowed to solidify slowly or when the
weld produced has a concave profile.
A weld with a more convex profile
that is frozen faster has a lower ten-
dency to produce this defect. Rutile
electrodes that have less fluid slag
produce a weld profile that is convex
and can be manipulated more readily
to avoid any undercut.
An extra thick zinc coating may
cause trouble in the vertical position
because when it is molten, it tends to
run down into the weld pool and
makes the slag difficult to control.
This can be prevented by maintaining
as short an arc length as possible.
Also , when welding galvanized
steel, hydrogen induced cracking of
the heat-affected zone may occur in
the base plate adjacent to the weld.
The precautions necessary for the
avoidance of cracking include such
measures as reduction in cooling rate
of the joint by the use of preheat or the
use of large diameter electrodes at
high currents. The hydrogen content
of a weld can be increased when it is
deposited on galvanized or zinc-rich
primed steel.
This extra hydrogen originates from
the pickling process in galvanizing, or
from the decomposition products of
primers. It may be necessary to either
remove primers from the vicinity of
the joint before welding or use a
higher preheating temperature than
would be used on uncoated steel.
Zinc-rich paints are available that
have been specially formulated such
that it is not necessary to remove the
coating from the weld path prior to
welding. A letter should be obtained
from the paint manufacturer stating it
to be "weldable."
A fairly extensive amount of re-
search has been carried out over many
years on the mechanical properties of
welds in zinc coated steels. Research
performed by the International Lead
Zinc Researc h Organization has
#hvac #welding #gipipe #chiller