WELDING DEFECTS

                                              WELDING DEFECTS

DEFECT: A flaw or flaws that by nature or accumulated effect in a part or product that unable to meet minimum applicable acceptance standards or specifications. The term designates Defects.

DISCONTINUITY: An interruption of the regular structure of a material, such as a lack of homogeneity in its mechanical, metallurgical, or physical characteristics. Discontinuity is not necessarily a defect.

WELD JOINT DISCONTINUITIES

       1.    MISALIGNMENT 

·         Weld joint shift by some distance.

·         Caused due to careless welding fit-up and uneven plate thickness welding.

·         Can prevented by checking straightness of joint at the time of fit-up/tacking.

·         Repair by using grinding, and match their nominal thickness to keep visually better.

  

        2.    UNDERCUT

·         Some portion remains unfilled near toe side of the weld bid called undercut.

·         Caused due to shift of welding center line, high ampere current passes, welding angle of electrode & rust.

·         Can prevented by Cleaning the plate before welding, setting proper amperage, training to the welder.

                  ·         As per undercut dimensions select the smaller diameter (low hydrogen) electrode                          and weld the undercut portion by preheating the same. 

       3.    UNDER FILL

·         It is the unfilled portion of the weld above the base plates that is proper bid height is not maintained then it is called as under fill.

·         Improper welding technique & high speed welding pass.

·         Can prevented by checking of bid height by using weld gauge time to time.

·         Wherever under fill is there needs to refill the welding to maintain proper bid height.

 

        4.    CONCAVITY & CONVEXITY

·         It is the cavity or dome like surface of weld toe observing in the fillet welds known as concavity or convexity.

·         Caused due to not given proper amperage and not maintain travel speed.

·         For repair needs to grind off the dome like welds and give the proper bid height & for concavity match the weld with plate by grind off near plate side weld.

                      

       5.    EXCESSIVE REINFORCEMENT

·         It is the weld deposition height over the base metal.

·         As per standard reinforcement should be 1/16” for Pipe & 1/8” for Plate or structure.

·         It is occur due to slow travel speed and low amperage.

·         For repair remove the excessive reinforcement by grinder and smooth the weld toe.

                                

        6.    OVERLAP

·         If the face of the weld beyond the toe of the weld known as overlap.

·         Caused due to improper welding technique, electrode angle & travel speed.

·         Overlap should be removed by grinding and make toe of weld smooth.

 

       7.    BURN THROUGH

·         When during welding an open hole has been completely melted on a sheet it is referred as a burn through.

·         It is caused due to excessive heat input.

·         Make a proper V preparation on melted portion and re-weld the burned weld portion with low heat input.

           

        8.    INCOMPLETE PENETRATION

·         When the deposited weld metal does not fill the required depth into the weld joint known as incomplete penetration.

·         Caused due to low amperage, fast travel speed, low preheat.

·         Repair by using back gouging (other side grind off and welding).

 

       9.    INCOMPLETE FUSION/LACK OF FUSION

·         Weld joint where the deposited weld metal does not make a cohesive bond with the base metal known as lack of fusion.

·         Caused due to low amperage, electrode angle, fast travel speed, uncleaned base metal and too short root gap.

·         Wherever lack of fusion is observed grind off it and re-weld the same to proper cohesive bond between deposited weld metal and base metal.

 

        10.    ARC STRIKE

·         It is the local weld trial before welding on base metal observed near the weld joint.

·         It is caused due to welder carelessness and not using trial plate with him for starting of welding.

·         Wherever arc strikes are found grinding or sanded by sander wheel, if found deep then must do the Dye penetration test after grinding.

       11.    INCLUSION

A.   SLAG (in SMAW)

·         A foreign particle is entrapped into the weld joint during welding known as slag inclusion.

·         Caused due to low amperage, not cleaned base metal before welding.

·         Can be prevent by proper cleaning and preheating the base metal.

·         Remove the inclusion by grinding and weld again.

B.   TUNGSTEN (in GTAW)

·         A tungsten particle is entrapped into weld metal.

·         Caused due to tungsten electrode is small, too high amperage, electrode dipped into the weld pool etc.

·         Repair by grinding and weld again.

 

       12.    SPATTER

·         Spatters are small particles expelled from the welding on adhere to base metal near the weld joint.

·         High amperage, long weld length etc.

·         Can be removed by chipping tool or grinding.

 

      13.    ARC CRATERS

·         Arc crater is the depression left after the termination of welding run.

·         Caused due to improper welding termination technique.

·         If no crack is generated into the crater then simply fill the crater and start the welding.

                            

       14.    CRACKS

·         Crack is the weld breaking line found on the welded metal surface or into the welded region.

·         Cracks have below types:

                   Longitudinal crack

                   Transverse crack

                   Crater crack

                   Throat crack

                   Toe crack

                   Root crack

                   Crack in heat affected zone

                   Hot crack etc.

 

      15.    POROSITY

·         It is the gas entrapped holes on the surface of the weld.

·         It can be single or cluster porosity.

·         Preheat may eliminates the porosity.

·         Rework by grinding and re-weld wherever needs.