The various types of welding defects we find on board ship

There are various types of arc welding defects while performing welding works on board ship, the following are the defects we find on arc welding:

• Cracks : it is a facture type of discontinuous development characterized by a sharp tip and high ratio of length and width to opening displacement.

• Porosity and blow holes : porosity is a group of small holes, whereas blow hole or gas pocket is a comparatively bigger isolated hole or cavity. They occur mainly due to the entrapped gases.

blow holes

gas pocket

           

         

The parent metal melted by means of the arc tends to absorb gases like hydrogen, carbon monoxide, nitrogen and oxygen, if they are present around the molten weld metal pool.

• Slag inclusion : Non metallic solid materials entrapped in the weld metal or between the weld and the base metal.
  
  
  

• Undercutting :

  

   In undercutting, a groove gets formed in the parent metal along the sides of weld bead.
  Groove reduces the thickness of the plate and thus the area along the bead, which in turn  weakens  the weld.

  
  

         

• Incomplete fusion and penetration : Incomplete fusion is a weld discontinuity in which fusion did not occur between weld metal and fusion faces.

          

This absence of fusion may occur at any location within the weld joint and may be present it in the fillet welds groove welds.

         Penetration is the distance from base plate

         top surface to the maximum extent of the

         solid piece of the weld.

          

 Incomplete joint penetration is described as a joint root condition in a groove weld in which weld metal does not extend through the joint thickness.

           It is the failure of filler metal or base metal

           to completely fill the root of the weld.

• Distortion : While welding a job, base metal under the arc melts, base metal ahead gets preheated and the base metal portion already welded starts cooling.
  
  
  
  

         

           

There is a good amount of temperature difference at various points along the joint and thus at any instant certain areas of base metal expend and others including weld bead contract.