Blowhole is a phenomenon in which the air in weld metal cannot release when such weld metal becomes solid.
Blowhole may appear inside or on surface of a weld, or focus or disperse inside a weld.
The existence of blow hole in a weld diminishes working section, load bearing strength and tightness of welded connection.
Form of crack
Longitudinal crack
·        Use welding materials incorrectly.
·        Considerable tension in welded connection.
·        Cold speed is high
·        Arrange weld layers inappropriately.
·        Welded connection is incorrect.
·        Use welding materials properly.
·        Release clamping force of welded connection and increase fill-up during welding.
·        Preheat welding materials, retain heat in welded connection to reduce cold speed of workpiece.
·        Arrange weld layers alternatively.
·        Use welded connection correctly, bevel, reduce clearances,…
Crack in arc ending area
·        Arc ending area is concave with impurities
·        Arc is not protected
·        Use welding devices properly, give specific regulations during making arc or ending arc.
·        Use seam welding plates at the arc beginning and ending positions so that such positions are arranged outside of welded connection.
Horizontal crack
·        Use welding materials inappropriately.
·        Cold speed is high
·        Welds are too small compared to the ending of the connection section.
·        Use welding materials appropriately
·        Increase current and size of welding electrode, execute thermal addition.