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Hello! My name is Mac and on behalf of expertvillage.com I am here to discuss MIG welding. Today I
would like to talk to you about weld defects. Now there are a number of weld defects that
can cause a weld to fail. There is porosity, cold lap, cracking, burn through; there are
any number of these things that can occur, lack of fusion is other one for instance.
Of the different types of weld defects probably one of the most common is a situation called
porosity, and it occurs when the gas coverage on the weld from the inert gas is not inadequate
and oxygen gets at the weld and causes it to bubble or be full of little gas pockets
that look like bubbles. This can be caused by a number of things and normally it is some
kind of stray air movement. For instance, an overhead ceiling fan or unit heater blowing
downwards can blow your gas coverage away, someone can open a door or a window and let
in a breeze or you can get porosity from welding over paint or on wet steel for instance. A
lot of welders make the mistake of thinking that the porosity is caused by not having
enough gas. In the case of porosity, if the welder goes to his regulator and starts to
turn up his gas pressure and you know the old saying about if a little bit is good then
a whole lot must be better, is not always the case. What can happen is, the gas pressure
can get so high that as it exits the gun the velocity is so great that it begins to cause
a Venturi effect. The gas flowing forward at a very high rated of speed begins to draw
air in around the edge of the cup the air deludes the shielding gas introduces nitrogen
and oxygen into the weld puddle and contaminates with porosity. So if you are having porosity
problems look somewhere else first. Solve all of the air infiltration problems, of forklifts
driving by very quickly creating a breeze, open windows and doors, fans running close
by, unit heaters and things like that. They are more than likely the cause of your porosity.
The another cause of weld failure is cracks and sometimes the cracks occur simply by welding
on steel that is too cold or chilled. The manufacturers of the welding wire will not
guarantee the quality of the welds if you weld on steel in ambient temperatures below
50 degrees Fahrenheit. So if the weld is fairly cool, you can get cracks. The weld puddle
cools off far too quickly.